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Is light pollution driving moth population declines? A review of causal mechanisms across the life cycle

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1. The night-time environment is increasingly being lit, often by broad-spectrum lighting, and there is growing evidence that artificial light at night (ALAN) has consequences for ecosystems, potentially contributing to declines in insect populations. 2. Moths are species-rich, sensitive to ALAN, and have undergone declines in Europe, making them the ideal group for investigating the impacts of light pollution on nocturnal insects more broadly. Here, we take a life cycle approach to review the impacts of ALAN on moths, drawing on a range of disciplines including ecology, physiology, and applied entomology. 3. We find evidence of diverse impacts across most life stages and key behaviours. Many studies have examined flight-to-light behaviour in adults and our meta-analysis found that mercury vapour, metal halide, and compact fluorescent bulbs induce this more than LED and sodium lamps. However, we found that ALAN can also disrupt reproduction, larval development, and pupal diapause, with likely negative impacts on individual fitness, and that moths can be indirectly affected via hostplants and predators. These findings indicate that ALAN could also affect day-flying insects through impacts on earlier life stages. 4. Overall, we found strong evidence for effects of artificial light on moth behaviour and physiology, but little rigorous, direct evidence that this scales up to impacts on populations. Crucially, there is a need to determine the potential contribution of ALAN to insect declines, relative to other drivers of change. In the meantime, we recommend precautionary strategies to mitigate possible negative effects of ALAN on insect populations.
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MAJOR REVIEW
Is light pollution driving moth population declines?
A review of causal mechanisms across the life cycle
DOUGLAS H. BOYES,
1,2,3
DARREN M. EVANS,
2
RICHARD FOX,
3
MARK S. PARSONS
3
and MICHAEL J. O. POCOCK
1
1
UK Centre for Ecology & Hydrology,
Wallingford, UK,
2
School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, UK and
3
Buttery
Conservation, Wareham, Dorset, UK
Abstract.1. The night-time environment is increasingly being lit, often by broad-
spectrum lighting, and there is growing evidence that articial light at night (ALAN) has
consequences for ecosystems, potentially contributing to declines in insect populations.
2. Moths are species-rich, sensitive to ALAN, and have undergone declines in Europe,
making them the ideal group for investigating the impacts of light pollution on nocturnal insects
more broadly. Here, we take a life cycle approach to review the impacts of ALAN on moths,
drawing on a range of disciplines including ecology, physiology, and applied entomology.
3. We nd evidence of diverse impacts across most life stages and key behaviours. Many
studies have examined ight-to-light behaviour in adults and our meta-analysis found that
mercury vapour, metal halide, and compact uorescent bulbs induce this more than LED
and sodium lamps. However, we found that ALAN can also disrupt reproduction, larval
development, and pupal diapause, with likely negative impacts on individual tness, and that
moths can be indirectly affected via hostplants and predators. These ndings indicate that
ALAN could also affect day-ying insects through impacts on earlier life stages.
4. Overall, we found strong evidence for effects of articial light on moth behaviour and
physiology, but little rigorous, direct evidence that this scales up to impacts on populations.
Crucially, there is a need to determine the potential contribution of ALAN to insect declines,
relative to other drivers of change. In the meantime, we recommend precautionary strategies
to mitigate possible negative effects of ALAN on insect populations.
Key words. Articial light at night, insect declines, Lepidoptera, meta-analysis, noc-
turnal, phototaxis, street lighting.
Introduction
Life on Earth has evolved over millions of years under predict-
able photic cycles, namely the daily lightdark cycle, seasonal
variation in day length, and lunar periodicity. These natural
cycles have become increasingly disrupted since the beginning
of the 20th century by anthropogenic light (Gaston et al.,
2017). There is growing evidence that these changes can have
profound impacts on biodiversity and associated ecosystem pro-
cesses (Hölker et al., 2010; Davies & Smyth, 2018; Sanders &
Gaston, 2018).
It is estimated that 23% of the worlds area experiences light-
polluted skies (Falchi et al., 2016), and the global area that is arti-
cially lit grew by 2% per year between 2012 and 2016 (Kyba
et al., 2017). Urban green space, domestic gardens, and road
verges are expected to be among the most frequently illuminated
habitats, though light pollution is also encroaching into less
human-inuenced areas, including biodiversity hotspots (Guetté
et al., 2018; Koen et al., 2018), as well as freshwater and marine
systems (Perkin et al., 2011; Davies et al., 2014). Furthermore,
rapid shifts are underway in the spectral composition of outdoor
lighting (Kyba et al., 2017; Davies & Smyth, 2018). Narrow spec-
trum lighting, such as sodium lamps (characterised by a warm,
yellow-orange light), is being replaced by LEDs, which are more
energy efcient but typically emit light over a broader range of
wavelengths (producing a cool, white light) (Taguchi, 2008; De
Almeida et al., 2014).
Nocturnal and crepuscular species are expected to be most
vulnerable to articial light. More than 60% of invertebrates
are estimated to be nocturnal (Hölker et al., 2010), including
7585% of Lepidoptera (Kawahara et al., 2018). Adult moths
Correspondence: Douglas H. Boyes, UK Centre for Ecology & Hydrol-
ogy, Wallingford, OX10 8BB, UK. E-mail: info@douglasboyes.co.uk
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological Society.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in
any medium, provided the original work is properly cited.
1
Insect Conservation and Diversity (2020) doi: 10.1111/icad.12447
famously y towards light (positive phototaxis) and, conse-
quently, this group has been comparatively well studied in the
context of light pollution. Furthermore, moths are ecologically
and evolutionarily diverse, functionally important across terres-
trial ecosystems globally, and have decades of high-quality data
on abundance and occurrence in certain parts of Europe. For
these reasons, moths are uniquely placed for understanding the
population-level impacts of ALAN on nocturnal insects more
broadly.
Long-term declines in moth abundance have been reported
from some parts of central Europe. In Great Britain, standardised
monitoring has revealed that 34% of the 390 commonest macro-
moths had statistically signicant declines between 1970 and
2016, with a 25% decline in a 442-species abundance indicator
over the same period (Randle et al., 2019; Hayhow
et al., 2019) and there is evidence for similar declines in
macro-moth abundance from the Netherlands (Groenendijk &
Ellis, 2011; Hallmann et al., 2020). The causes of these declines
are incompletely understood, although climate change (Conrad
et al., 2002; Martay et al., 2017) and habitat degradation are
thought to be largely responsible (Fox, 2013; Fox et al., 2014).
Yet, there is growing concern that light pollution may have a role
in moth declines (e.g. van Langevelde et al., 2018), and articial
light has been suggested as a driver of insect declines more
broadly (Grubisic et al., 2018; Owens et al., 2020).
Anthropogenic light is known to have wide-ranging effects on
moth behaviour and physiology, and recent studies have found
correlative evidence linking light pollution to the negative popu-
lation trends of some European moths (van Langevelde
et al., 2018; Wilson et al., 2018). However, eld studies have
delivered mixed conclusions on the effects of night-time lighting
on moth communities (Spoelstra et al., 2015; Plummer
et al., 2016; Macgregor et al., 2017; White, 2018; Péter
et al., 2020). Thus, there is a clear need to elucidate the mecha-
nisms by which ALAN might be affecting moth populations.
Here, we substantially build upon previous reviews on the
effects of light pollution on moths (Frank, 1988; Macgregor
et al., 2015) and insects more broadly (Eisenbeis &
Hänel, 2009; Owens & Lewis, 2018; Desouhant et al., 2019),
by adopting a holistic approach to consider the potential mecha-
nisms by which light affects moths throughout their entire life
cycle. We dene mechanismsas any way that ALAN can affect
the physiology, behaviour, or processes of individual moths, and
thereby potentially impact on moth populations. Relevant
research from outside the context of ecological light pollution
is synthesised (e.g. within the pest control literature) with a
growing number of newly published studies. We also conduct
a network meta-analysis of studies to reveal which lighting tech-
nologies are the most effective at eliciting ight-to-light behav-
iour for both moths and all nocturnal insects. Having
considered mechanisms, we then seek to determine the extent
to which individual-level responses translate to the population
level (including past applications of light for pest control) and
so critically assess the quality of evidence linking ALAN with
changes in moth assemblages or population trends. Finally, we
consider the options for mitigating the disruptive impacts of
lighting on moth behaviour and identify knowledge gaps for
future research.
Methods
Scientic articles were located using Web of Science and Google
Scholar, using an iterative process. Searches were conducted
with the following terms: MothOR LepidopteraAND
Light*OR Phot*, followed by supplementary terms includ-
ing circadian, activity, diel, attraction, phototaxis, behaviour,
development, reproduction, diapause, predation, and parasitism.
Additional articles were located through searching reference lists
(snowballing) and subsequent citations (reverse snowballing).
This was repeated until no new relevant articles were found.
We deemed a systematic search to be inappropriate for this
review given the very broad scope of relevant articles, spanning
many disciplines, which we had already located.
In order to answer the specic question of which types of out-
door lighting technology induce the strongest ight-to-light
responses for both moths and all nocturnal insects, a fully sys-
tematic search was conducted. Data from 14 qualifying studies
were entered into two Bayesian network meta-analyses. Details
of the search methodology, inclusion criteria, data extraction,
and the meta-analysis models are given in the Supporting Infor-
mation Appendix S1.
The thorough search of the literature produced evidence of
direct and indirect impacts of ALAN throughout the moth life
cycle, with evidence from elds as diverse as ecology, physiol-
ogy, cellular biology, and pest management. We consider poten-
tial impacts sequentially from the adult stage to the egg
(Figure 1), clearly describing the mechanisms and our assess-
ment of the weight of evidence for each impact. We give priority
to eld or laboratory experimental studies focusing on moths,
but also include observations and hypothesised effects
(or effects demonstrated in other taxa). Where possible, the
intensity and type of light (see Box 1) responsible for a result
are reported.
Direct effects of articial light at night on moths
Adult life stage
Moths are typically only adults for a small proportion of their
entire life cycle; however, adults are responsible for reproduc-
tion, and in the vast majority of species, also dispersal. Conse-
quently, there is disproportionate potential for ALAN to impact
moth populations via mechanisms that affect adults.
Suppression of activity. There is clear evidence that arti-
cial light can suppress the activity of adult moths, even at low
levels, potentially preventing them from carrying out important
behaviours. The onset of activity in nocturnal moths is often
controlled by a drop in ambient light levels and laboratory
experiments have found that the critical light level at which
moths become active is typically below 1 lux (Persson, 1971;
Dreisig, 1980). This means that moths resting in the vicinity
of night-time lighting could fail to commence nocturnal activity.
Experimentally illuminating oak tree trunks with LEDs at 10 lux
strongly reduces the numbers of female Operophtera brumata
(Linnaeus; Geometridae) caught in funnel traps (relative to
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
2 Douglas H. Boyes et al.
BOX 1. THE INTENSITY AND SPECTRAL PROFILE OF OUTDOOR LIGHTING
The two most biologically signicant properties of light are its intensity and its spectral composition. Lux is the SI unit of
luminance, which is widely used by urban planners, as well as ecologists, despite it representing the intensity of light as per-
ceived by the human eye. This means that lux not a good metric when examining ecological impacts, because potentially rel-
evant spectral information is omitted (Longcore & Rich, 2004). For instance, two lamps might produce the same value of lux,
while emitting this light over different parts of the spectrum. For insects, the spectral composition of night-time lighting may
be more biologically signicant than its intensity (Longcore et al., 2015). Common outdoor lamp types varying signicantly
in their spectral output. Low-pressure sodium (LPS) is almost monochromatic (producing only orange light), while high-
pressure sodium (HPS) produces light over a wide range of wavelengths (including some blue and green light). Light-emitted
diodes can be any colour, but LEDs used for amenity lighting tend to emit light across the visible spectrum to produce white
light. Mercury-vapour and metal halide lamps also produce white light, but with a signicant amount of ultraviolet light. The
former was previously commonly used for street lighting but has been widely phased out in Europe.
Lux Comparable value References
103 000 Daylight sunny day Rich and Longcore (2013)
100010 000 Overcast day Rich and Longcore (2013)
400600 Ofce Rich and Longcore (2013)
100300 Home Rich and Longcore (2013)
10 Lit parking lot Rich and Longcore (2013)
3.6 (range: 0.116, n= 30) Verges and hedgerow adjacent to street lighting D. H. Boyes, unpublished data
0.10.5 Skyglow Eisenbeis (2006)
0.10.3 Full moon; clear sky Rich and Longcore (2013)
0.001 No moon; clear sky Rich and Longcore (2013)
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 3
controls), suggesting that light inhibits their activity (van Geffen
et al., 2015a). Moths that y from darkness into an illuminated
area can become inactive, sometimes remaining so for the rest
of the night (Frank, 2006). This may be as the exposure to light
triggers the day-time response of ceasing activity, possibly
mediated through the light-adapted and dark-adapted states of
the compound eye in insects (Robinson, 1952; and see
Walcott, 1969; Laughlin & Hardie, 1978). It has been proposed
that a sudden change in light levels effectively blinds a moth
until its eyes have readjusted (Frank, 1988), something that
can take over 30 min in some species (Bernhard &
Ottoson, 1960).
Fig. 1. Evidence for effects from articial light on moths across the life cycle, as discussed in this review. Shaded boxes show effects with strong evi-
dence, i.e. experimentally demonstrated in moths for at least one species in the eld or laboratory, using eld-realistic levels of light. Lighter boxes are
effects with anecdotal evidence in moths, or effects documented at higher intensities of light, or strong evidence of a comparable effect in another insect
taxon. Dashed boxes represent plausible effects but little or no evidence as yet.
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
4 Douglas H. Boyes et al.
There is seemingly no evidence of the opposite phenomenon:
diurnal Lepidoptera (day-ying moths or butteries) becoming
active at night in articially lit environments, although this occu-
pation of the night light nichehas been observed in other diur-
nal taxa, such as jumping spiders (Wolff, 1982; Frank, 2009).
Disruption of adult feeding. Many adult moths feed, typi-
cally on nectar from owers, which increases their longevity
and fecundity (Leather, 1984; Leahy & Andow, 1994; Tisdale &
Sappington, 2001; Song et al., 2007) and there is strong evidence
that ALAN can disrupt his behaviour. Night-time feeding in four
species of macro-moth was inhibited by articial light at an
intensity of 15 lux (produced by green, white, or red LEDs),
compared to unlit controls (van Langevelde et al., 2017). Consis-
tent with the authorsexpectations, shorter wavelengths of light
(bluer) were most effective at suppressing feeding; however,
even the red treatment (producing little light below 600 nm)
reduced the probability of feeding by more than half. Negative
impacts on feeding are irrelevant for the moth species that do
not feed as adults (Norris, 1936; Frank, 1988); nevertheless,
night-time lighting may have comparable effects on other key
behaviours (e.g. reproduction).
Eliciting ight-to-light. Moths famously exhibit positive
phototaxis (ight-to-light), though this is also found in many
other insect groups. The consequences for an individual that
has been attracted to a light range from a brief disruption of rou-
tine behaviours (small tness cost) through to mortality (high t-
ness cost, especially if the individual had yet to reproduce);
however, the costs of this behaviour at the population-level are
poorly known.
Several explanations have been put forward to explain posi-
tive phototaxis in insects (summarised by Nowinszky, 2003).
These include the light-compass theory, whereby lamps are
being mistaken for a celestial cue used for orientation (Baker &
Sadovy, 1978), and the idea that bright light simply dazzles
night-ying insects (Robinson & Robinson, 1950). Upon
encountering a light source, a moth can spiral around it, crash
into it, settle some distance from it, or simply ignore it; no single
theory successfully accounts for this diversity of behaviours
(Frank, 2006).
Whilst the reasons for ight-to-light remain unresolved, dif-
ferent lamp types are known to elicit this behaviour to varying
degrees. Shorter wavelengths of light, particularly ultraviolet,
are the most effective at attracting moths (van Langevelde
et al., 2011; Barghini & de Medeiros, 2012). Taxonomic families
of Lepidoptera do not respond uniformly to light (Merckx &
Slade, 2014); for instance, Noctuidae are more strongly attracted
to shorter wavelengths than Geometridae (Somers-Yeates
et al., 2013). Moths can also be sensitive to the polarisation of
light (Belušicˇet al., 2017). Polarised light pollution is thought
to be particularly harmful to aquatic insects (Horváth
et al., 2009), though its potential effects on moths remain
unexplored.
Many studies have compared the catches resulting from vari-
ous types of bulbs commonly used for street lighting (Table 1).
We included 14 studies in a meta-analysis; these either had data
available or the effect sizes could be obtained from the
Table 1. Studies that have compared the number of moths and/or
insects attracted to different bulb types commonly used for outdoor light-
ing. Note that some of these studies have compared additional bulb types
not reported here (because these are not widely used for outdoor lighting,
e.g. coloured LEDs).
Study
Relevant bulb
types compared Results
Rydell (1992)*MV; HPS; LPS MV attracted more insects
than HPS. LPS did not
attract any insects,
compared to unlit controls
Blake
et al. (1994)*
MV; LPS Eight times more insects
seen around MV lamps
than LPS
Eisenbeis (2006),
and studies
therein*
MV, HPS MV attracted more insects
than HPS
Huemer
et al. (2010)
MH; HPS; warm
and cool LED
All insects:
MH > HPS > cool LED >
warm LED. Moths:
MH > HPS > cool
LED = warm LED
Barghini and de
Medeiros (2012)
MV; HPS MV attracted more insects
and more moths than HPS.
Somers-Yeates
et al. (2013)
MH, HPS In moths, MH was more
attractive to Noctuidae
than HPS. Geometridae
showed no difference
Soneira (2013) MH; LED MH caught more insects and
moths than LED.
Pawson and
Bader (2014)
HPS; LED (of
different colour
temperatures)
LED caught more insects
than HPS. Catches from
different LEDs did not
differ signicantly
van Grunsven
et al. (2014a)
MV; MH, LPS,
LED
MV attracted many more
insects than the other lamp
types (which each attracted
comparable numbers)
Longcore
et al. (2015)
CFL; LED CFL caught more insects
and moths than LED
Poiani
et al. (2015)
CFL; LED CFL caught more insects
and moths than LED
Justice and
Justice (2016)
CFL; Warm and
cool LED
No signicant difference for
neither all insects nor just
moths
Wakeeld
et al. (2016)
CFL; Warm and
cool LED
CFL attracted more insects
than LEDs. No signicant
difference between warm
and cool LEDs
Pintérné and
Pödör (2017)*
MH; HPS MH caught more moths than
HPS
Wakeeld
et al. (2018)
MH, LED, HPS MH caught ve times as
many insects than LED or
HPS
van Grunsven
et al. (2019)
MV; LED MV caught twice as many
insects as LED
MV, mercury-vapour; HPS, high-pressure sodium; LPS, low-pressure
sodium; MH, metal halide; LED, light-emitting diode; CFL, compact
uorescent lamp. *Asterisks indicate that the study was unable to be
included in the quantitative meta-analyses (Figure 2; Supporting
Information Appendix S1).
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 5
publication (Supporting Information Appendix S1). High-
pressure sodium (HPS) is the incumbent street light technology
across much of Europe so we compared the capture rates of
insects of HPS lamps to other bulb types, using capture rate as
an indicator of the ight-to-light response. Relative to HPS,
LED lamps with cool colour temperatures catch 0.6 times the
number of moths on average than HPS (however, the 95% cred-
ible intervals (CrI) overlap slightly with no difference; range:
-1.050.33; Fig. 2a). There was no detectable difference between
the attractiveness of LEDs of cooler or warmer colour tempera-
tures (Supporting Information Fig. S2). Metal halide (MH) and
mercury-vapour (MV) lamps (both rich in ultraviolet light)
attract three and ve times more moths, respectively, than HPS.
Averaged across 10 studies that reported order-level data,
Lepidoptera only made up 11% of the total insects attracted to
light [the third most abundant order after Diptera (48%) and
Coleoptera (11%)]. Despite this, moths show comparable
responses to the catches of all orders pooled (Fig. 2; Fig. S2),
with a strong correlation in the treatment pairwise mean differ-
ences between only moths and all insects (Pearsons rho: 0.94,
n= 11). This indicates that moths are a suitable model group
for nocturnal insects more broadly (at least with respect to
phototaxis).
These studies have implicitly or explicitly assumed that the
number of insects attracted to a certain lighting type is a suitable
proxy for the bulbs ecological impact. This may not necessarily
be valid. For instance, a certain type of bulb may catch few
insects because it is suppressing ight activity, not because
insects are insensitive to it. Moreover, the approach fails to con-
sider negative impacts on fundamental life processes
(e.g. reproduction) and other life stages (Fig. 1).
Nonetheless, the number of insects drawn to a given lighting
type may be a reasonable proxy for its ecological impact pro-
vided that a biologically signicant portion of the individuals
attracted either: (i) suffer direct mortality or (ii) remain effec-
tively trapped, being unable to carry out normal behaviours.
Direct mortality can occur due to collision with a hot bulb
(although this is presumably only applicable to less energy-
efcient lamps), or exhaustion if the moth continually circles
the light. Another source of mortality is predation, which can
be heightened around street lights (see section on indirect
effects). It has been estimated that 33% of insects that are
attracted to street lights perish (Eisenbeis, 2006); however, it is
not clear how this gure was obtained. It remains unknown what
proportion of the moths that are initially attracted to a street light
die from collision with the bulb, succumb to exhaustion, are pre-
dated, or y away unharmed.
A commonly discussed concern in the context of ight-to-
light behaviour is trap effects (Macgregor et al., 2015), or a
vacuum cleanereffect (Eisenbeis & Hänel, 2009). These
hypothesise that moths are continually drawn in from the sur-
roundings, depleting those populations, with the illuminated area
forming a sink habitat. At present, there is little evidence to sup-
port this idea, though this could partly reect the challenges of
detecting it. A study in Japan found that the abundance and spe-
cies richness of moths caught in a light trap does not increase
over consecutive nights, suggesting that individuals can escape
the lamps radius of attraction (Hirao et al., 2008).
We believe it is useful to distinguish a trap effect from a con-
centration effect (Figure 3), whereby moths are drawn in from
surrounding habitats but are otherwise not negatively impacted.
Such outcomes are likely to be context-specic, for instance, a
trap effect is more likely if the lit area comprises entirely unsui-
table breeding habitat (e.g. car parks, airports, industrial units).
An alternative idea is the disruption effect, whereby behaviour
is impacted locally, but individuals are not drawn in from sur-
rounding areas.
There are reasons why ight-to-light behaviour might be
expected to have a limited impact at the population level. The
distance at which moths are drawn to lamps is generally thought
to be small (Frank, 1988; Nowinszky, 2004). The effective range
of a 125 w mercury-vapour lamp has been estimated at 35m
(Baker & Sadovy, 1978), while others have reached a gure an
order of magnitude greater (Robinson & Robinson, 1950;
Robinson, 1960; Degen et al., 2016). A mark-release-recapture
study estimated the proportion of individuals recaptured when
ying 01 m past a 6 w actinic light was only up to 10% for noc-
tuids, 15% for geometrids, and 50% for erebids (Merckx &
Slade, 2014), while a similar study using 15 w actinic lamps
reported most recaptures occurred at release distances <30 m,
and typically <10 m (Truxa & Fiedler, 2012) and another study
found that only 25% of moths released 2 m from a 6 w actinic
light were recaptured by the trap (van Grunsven et al., 2014b).
All insects(b)
(a) Only moths
Mean Difference (95% CrI)
Compared with HPS, n=4
0.31 (−0.50, 1.1)
−0.28 (−0.84, 0.32)
−0.41 (−1.1, 0.33)
1.0 (0.37, 1.7)
0.88 (0.18, 1.7)
CFL, n=4
LED (cooler), n=9
LED (warmer), n=6
MH, n=4
MV, n=3
0−2 2
Mean Difference (95% CrI)
Compared with HPS, n=5
1.0 (0.20, 1.8)
−0.50 (−1.1, 0.048)
−0.55 (−1.3, 0.15)
1.1 (0.48, 1.7)
1.6 (0.83, 2.3)
CFL, n=4
LED (cooler), n=9
LED (warmer), n=6
MH, n=5
MV, n=3
0−2 3
Fig. 2. Forest plots from network meta-analyses on the abundance of
(a) Lepidoptera and (b) all insects attracted to different types of lamps
commonly used for street lighting, relative to the incumbent technology:
high-pressure sodium. Error bars show 95% credible intervals. Note that
mean differences are on a log
e
scale, so each unit represents a 2.7-fold
change in number. The number of contributing studies is shown for each
treatment. LEDs with colour temperatures of 2700 k to 3500 k were
grouped as warmer, while those of 4000 k to 6500 k were cooler.
Abbreviations used in the plots: high-pressure sodium (HPS); compact
uorescent lamp (CFL); light-emitting diode (LED); metal halide
(MH); mercury-vapour (MV). The methods are given in the Supporting
Information Appendix S1, along with results for each treatment pairwise
comparison; Supporting Information Appendix S2 reports the 39 studies
found by the systematic search and the rationale for inclusion or exclu-
sion; Supporting Information Appendix S3 lists the treatment estimates
from the studies included in the meta-analyses.
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
6 Douglas H. Boyes et al.
These studies have investigated the lighting types used in moth
traps. The radius of attraction of the lamps most commonly used
for outdoor lighting (e.g. HPS, white LEDs) remains largely
untested but might be expected to be lower as these emit little
or no ultraviolet light. Thus, the idea that moths are routinely
lured into urban areas over great distances (Eisenbeis &
Hänel, 2009) seems unlikely.
The population-level ramications of phototaxis by moths
may also be limited by the fact that females are less strongly
affected. A 4-year study using light traps found that males were
more frequently captured for 45/51 species examined, with only
15% of the 9,926 individuals caught being female
(Williams, 1939). The actual sex ratios of these moth popula-
tions are not known; however, experimental evidence for male-
biased ight-to-light behaviour has been reported, with males
from two species being 1.6 times more likely to y to light
(Altermatt et al., 2009). This is most likely because males are
more mobile (thus are more likely to enter the radius of attrac-
tion), as opposed to being more strongly attracted to light
(Degen et al., 2016).
Evidence that ight-to-light behaviour can have negative
population-level effects on moths comes from the discovery that
individuals of the micro-moth Yponomeuta cagnagella (Hübner;
Yponomeutidae) from urban areas appear to have evolved to be
less attracted to light (Altermatt & Ebert, 2016). Larvae were
reared in a common garden setting after being collected in north-
western Switzerland and eastern France from ve rural areas and
ve light-polluted sites (albeit all within a single city: Basel).
Fig. 3. Three hypothetical impacts of light on moths (adapted from Macgregor et al., 2015), in terms of their populations and the ecosystem functions
they provide. Crosses represent adult moths and ovals represent larvae. [Color gure can be viewed at wileyonlinelibrary.com]
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 7
Adults from urban sites were 30% less likely to be caught by the
light trap (6 w actinic lamp), which was 5.7 m away at the oppos-
ing end of a mesh cage. Further evidence to test the generality of
this nding would be valuable. Evolution by moths in response
to anthropogenic lighting has long been hypothesised
(Frank, 1988) and may be expected given articial light at night
can represent a strong selective pressure (Hopkins et al., 2018).
If an evolutionary change towards reduced phototaxis was wide-
spread among moths, light trap catches would be expected to
decrease in light-polluted areas over time. Yet, in the
Rothamsted Insect Survey (a UK-wide, long-term systematic
monitoring scheme), abundance trends from locations where
light pollution had increased from 1992 to 2000 were not more
negative than trends at sites that remained dark (Conrad
et al., 2006).
Negative phototaxis. There is limited evidence that adult
moths avoid illuminated areas at night, though this may be due
to the challenges of studying the behaviour in insects. Certain
vertebrate taxa are known to be repelled by articial light at
night, including some bats (Lewanzik & Voigt, 2017) and some
authors consider it likely that certain moths exhibit comparable
behaviour (Robinson, 1952). One species of moth, Amphipyra
tragopoginis (Clerck; Noctuidae), is infrequently seen in light
traps, compared to its abundance in suction samples, so is prob-
ably is poorly attracted to light (Taylor & Carter, 1961). Given
the typical adult behaviour of this species is to scuttle for cover
when exposed to light (Waring & Townsend, 2017), it is plausi-
ble the species may actively avoid lit areas at night.
Disruption of short and long-distance movements. It has
been hypothesised that linear sections of street lighting may dis-
rupt movement in moths, potentially leading to population frag-
mentation (Frank, 2006). A grid of 12 experimental street lights
(4 ×3) tted with ight interception traps found that the two
lamps in the middle caught fewer moths than lights on the edge
of the grid, which the authors propose is evidence that street
lighting can interrupt short-distance moth dispersal (Degen
et al., 2016). However, the lamps in the centre may also have
been less effective at attracting moths due to elevated back-
ground illumination from the surrounding edge lights
(Bowden, 1982). Furthermore, the ight intercept traps were
lethal, thus, movement is likely to be more signicantly restricted
than at regular street lights, where a proportion of the moths that
were initially attracted would continue past unharmed.
Light pollution has been suggested as a potential issue for
moths that use celestial cues to orientate during long-distance
dispersal, such as Noctua pronuba (Linnaeus; Noctuidae)
(Sotthibandhu & Baker, 1979) and Agrotis exclamationis
(Linnaeus; Noctuidae) (Baker, 1987). These behaviours are only
known to occur routinely in a select number of highly abundant
moths, and it is questionable whether local populations of these
species are dependent on effectively navigated long-distance
movements. Celestial cues are not exclusively used for orienta-
tion, with some moths using a magnetic compass (Baker &
Mather, 1982). Furthermore, migration in Lepidoptera typically
occurs at high altitudes (Wood et al., 2009) so is unlikely to be
affected by direct illumination from articial lights, although it
is plausible that diffuse anthropogenic light pollution (sky-
glow) could interfere with this process.
Impacts on reproduction. Reproduction in moths is closely
linked to the natural light cycle and there is clear evidence that
ALAN (especially at high levels) can impact reproduction through
several different mechanisms. The synthesis and release of female
sex pheromones in moths are typically timed using the day-night
cycle (Groot, 2014). Overnight illumination of 17 lux inhibits pher-
omone production in female Mamestra brassicae (Linnaeus; Noc-
tuidae), with only a third of the amount produced under shorter
wavelengths (green LEDs), relative to dark controls (van Geffen
et al., 2015b). The same lighting treatments also signicantly
altered the chemical composition of the pheromone blend. This
reduction in the quantity and quality of pheromones is hypothe-
sised by the authors to correspond to reduced mating success.
Female pheromone production and callingbehaviour (dur-
ing which the pheromones are released) is inhibited by continu-
ous lighting in cultures of Dioryctria abietella (Denis &
Schiffermüller; Pyralidae) (Fatzinger, 1973), and a similar effect
is observed in Helicoverpa assulta (Guenée; Noctuidae)
(Kamimura & Tatsuki, 1994). In Trichoplusia ni (Hübner; Noc-
tuidae), the release of pheromones is increasingly inhibited by
light intensity from 0.3 to 300 lux (Sower et al., 1970). Calling
in female Plodia interpunctella (Hübner; Pyralidae) is not sup-
pressed by constant light, which may be because this is a pest
of stored grain that has adapted to survive without natural day-
night cycles (Závodská et al., 2012; Groot, 2014). Yet, calling
in female Ephestia kuehniella Zeller (Pyralidae), another stored
grain pest, is suppressed by constant light, while the diel rhythm
persists in continual darkness: a characteristic of circadian regu-
lation (Závodská et al., 2012). Similar circadian rhythms in sex
activity have been demonstrated in several other moths from nat-
ural habitats (Groot, 2014).
The production of mature sperm in moths is also closely linked
to the diel cycle and can be disrupted by ALAN. Under natural
day-night cycles, sperm is released rhythmically through the repro-
ductive tract towards the duplex (where it is stored until mating);
however, continuous light can disrupt this sequential release of
sperm, meaning little reaches the duplex and the males are effec-
tively sterile (Giebultowicz et al., 1990; Bębas et al., 2001; Seth
et al., 2002). Male sterility, or signicantly depressed fertility, in
response to continuous light has been shown in laboratory cultures
of moths from the families Noctuidae (Hagan & Brady, 1981;
Bębas & Cymborowski, 1999), Pyralidae (Lum & Flaherty,
1970; Riemann & Ruud, 1974; Cymborowski & Giebułtowicz,
1976), and Erebidae (Giebultowicz et al., 1990). However, the
phenomenon is not universal since Cydia pomonella (Linnaeus;
Tortricidae) does not appear to show adverse impacts on male
reproductive capacity from continuous lighting (Giebultowicz &
Brooks, 1998).
Articial lights may also disrupt moth reproduction by
directly reducing the incidence of copulation. Mating is gradu-
ally inhibited by light levels above 0.3 lux in T. ni under labora-
tory conditions, although very bright light (>300 lux) is required
to completely suppress the behaviour (Shorey, 1966). This pro-
cess is temperature dependent in Chilo suppressalis (Walker;
Crambidae); for instance, 5 lux is sufcient to suppress mating
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
8 Douglas H. Boyes et al.
at 30C, but 600 lux is required at 15C (Kanno, 1980). Light
may also disrupt copulation by suppressing male ight activity,
or cause males to exhibit positive phototaxis, diverting them
away from females. Low levels of light (0.10.9 lux) cause male
Lymantria dispar (Linnaeus; Erebidae) to y less directly
towards females (Keena et al., 2001).
When oak trunks are illuminated with 10 lux, the proportion of
mated O. brumata females drops by half under longer wave-
lengths (red LEDs) and a quarter under shorter wavelengths
(green LEDs), relative to dark controls (van Geffen
et al., 2015a). This reduction may be due to disrupted phero-
mone production by females, inhibition of mating behaviour,
suppression of male ight activity, or males being distracted
from females by ying towards light (or a combination thereof ).
The authors also deployed traps baited with synthetic female
pheromone and found a smaller (but statistically signicant)
drop in males caught under the lighting treatments. This suggests
that the male response to female pheromones is disrupted by
light, but that the observed drop in mated females is likely to
be predominately attributable to disrupted pheromone release
or suppressed mating behaviour.
Articial light might also affect oviposition in moths. Moder-
ate light levels (840 lux) produced by an incandescent bulb sig-
nicantly reduce the number of eggs laid by P. interpunctella
(Sambaraju & Phillips, 2008). Suppression of oviposition by
light has been demonstrated for several other species under lab-
oratory conditions, though this has typically been tested with
continuous bright light (>200 lux) (Broodryk, 1971; Henne-
berry & Leal, 1979; Skopik & Takeda, 1980; Ismail
et al., 1988). The opposite effect, whereby oviposition is con-
centrated around articial lights, has been reported anecdotally
(Frank, 1988). For instance, larval infestations of Helicoverpa
armigera (Hübner; Noctuidae) in cornelds were several times
higher in the vicinity of light traps (Martin & Houser, 1941).
This is may lead to reduced larval tness through intensied
intra-specic competition.
As ova
We found no evidence that articial light, at the intensities
normally found outdoors, can impact moth tness during the
egg stage. The diel timing of hatching is under circadian control
in some moths, although constant light does not seem to prevent
hatching (Minis & Pittendrigh, 1968). Furthermore, photoperiod
is not an important cue for seasonality in moth ova; hatching is
usually controlled by temperature (Du Merle, 1999; Visser &
Holleman, 2001). The adult fecundity of three tortricids is
affected by the photoperiods experienced by the ova and rst
instar larvae (Deseo & Saringer, 1975); however, it is not clear
whether this effect would also occur at eld-realistic levels of
articial light during the night.
Larval stage
Feeding and development. Many moth larvae are noctur-
nal feeders and we found some evidence that ALAN could affect
their physiology and behaviour, although several plausible
mechanisms of ALAN on moth larvae remain to be tested.
Negative developmental effects from low levels of ALAN
have been demonstrated experimentally in two noctuids larvae.
Male M. brassicae larvae reared under 7 lux of white and green
LEDs at night reached a lower nal body mass, relative to dark
controls (van Geffen et al., 2014). No difference was observed
for female larvae, nor males reared under red LEDs. In Apamea
sordens (Hufnagel; Noctuidae), larvae experiencing dark nights
achieved signicantly higher body mass after 10 weeks, com-
pared to those reared under HPS lamps (Grenis &
Murphy, 2019). Larval survival was not affected in either study;
however, the authors hypothesise that the reduction in nal lar-
val mass would translate to reduced adult tness (e.g. reduced
fecundity).
Moth larvae of many species feed predominately at night,
when fewer predators and parasitoids are active (Porter, 2010).
Positive phototaxis has been observed in the larvae of several
moth species (De Ruiter & van der Horn, 1957; Buck &
Callaghan, 1999), which could theoretically cause caterpillars
to be drawn away from their hostplants. Outdoor lighting might
also suppress feeding behaviour in nocturnal caterpillars (trig-
gering the normal day-time response of inactivity), with knock-
on effects for larval development, though this has yet to be
tested.
Diapause and pupation. Diapause is a state of dormancy
that enables insects to survive unfavourable conditions
(e.g. winter) and we found evidence that lighting can readily dis-
rupt diapause, although the impact on populations remains
unknown. Night-time lighting can prevent multivoltine species
from entering winter diapause, a process that is typically initiated
by shortening day lengths (Adkisson, 1966; Peterson &
Hamner, 1968; Bell et al., 1975). White and green LEDs at an
intensity of 7 lux inhibits M. brassicae larvae from entering dia-
pause (van Geffen et al., 2014), which instead enter a non-
diapausing pupal stage. Fluorescent lamps extending daylength
in eld plots to 17 h results in 70% of C. pomonella and 76%
of Ostrinia nubilalis (Hübner; Crambidae) failing to enter dia-
pause, compared to 0% of larvae in plots with natural day-night
conditions (Hayes et al., 1970). The authors state that the larvae
that fail to enter diapause would perish over the winter. In a
greenhouse study, 60 lux of LED inhibited diapause in the leaf-
miner Cameraria ohridella Deschka & Dimi
c (Gracillariidae),
which the author concludes could lead to either increased out-
breaks (more generations per year) or local extinction (if pupae
that failed to enter diapause died over winter) (Schroer, 2019).
Pupal stage
We could nd no documented effects of articial lighting in
the pupal stage, and we conclude that this unlikely to be an
important mechanism whereby ALAN affects moths. It is plausi-
ble that outdoor lighting could cause mistimed adult emergence
in temperate moths that use photoperiod cues to detect seasonal-
ity, which could disrupt population synchronicity. It has been
suggested that the emergence of adults in some species is
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 9
synchronised with lunar periodicity, perhaps to maximise the
chances of nding mates (Nemec, 1971; Nowinszky
et al., 2010). There is little evidence of this, however, and cycli-
cal dynamics appearing in light trap data are considered an arte-
fact arising from the reduced sampling effectiveness around full
moon (Williams et al., 1956; Yela & Holyoak, 1997).
Diel emergence synchronicity could be theoretically disrupted
by light pollution, as certain species tend to emerge at the same
time of day (e.g. Bergh et al., 2006; Calatayud et al., 2007), pro-
vided the emergence cue involved is photic and not thermal. The
reasons for this behaviour are unclear but may include promoting
population synchronicity between males and females, as well as
avoiding predation.
Molecular and physiological effects (on various life stages)
The physiological and molecular-level effects of ALAN on
moths are not well known. Melatonin is a highly conserved hor-
mone found in most living organisms, including insects
(Hardeland & Poeggeler, 2003; Zhao et al., 2019). Its synthesis
and release typically happen during darkness and are suppressed
during the daytime (Bloch et al., 2013). Melatonin is involved in
the circadian regulation of adult moths (Linn et al., 1995; Lam-
pel et al., 2005), and the hormone has been found in moth larvae
(Itoh et al., 1995) where it is likely to perform a similar role. Mel-
atonin is also a powerful antioxidant, having a protective role
within cells (Reiter et al., 2017). It is plausible, though untested,
that light pollution could suppress melatonin synthesis in moths,
leading to oxidative stress and cellular damage. The potential
implications of this for moth tness are unknown but might be
limited given their short life cycles.
All insect life stages can be vulnerable to direct exposure to
certain wavelengths of light. The negative effects of ultraviolet
(UV) light at a cellular level are well known, for instance, its abil-
ity to damage DNA molecules (Sinha & Häder, 2002). In addi-
tion to its lethal effects on insects (Beard, 1972), UV light can
cause changes in the expression of neuropeptides in adult moths
(Wang et al., 2018). Prolonged irradiance by shorter wave-
lengths of visible light can cause high mortality in various life
stages of a fruit y, a our beetle, and a mosquito (Hori
et al., 2014). However, it is doubtful that many insects experi-
ence the requisite intensities from articial lighting while
outdoors.
Indirect effects of articial light at night on moths
It is becoming increasingly apparent that effects mediated
through other taxa must be considered to predict the impacts of
global change. Indirect effects can be strong in ecological com-
munities exposed to articial light (e.g. Bennie et al., 2018b;
Sanders et al., 2018); however, species interactions remain rela-
tively poorly studied in the context of light pollution (Sanders &
Gaston, 2018).
Moths may be indirectly affected by night-time lighting via
plants; this could occur if articial light modies the quantity
and quality of plants, or if ALAN creates a phenological
mismatch between moths and the plants they are reliant
on. Such effects are most likely to act on the larval stage, which
is entirely dependent on hostplants in the majority of lepidop-
terans, though weaker effects might also be observed in species
with nectar-reliant adults. Top-down indirect effects can occur
through predation and parasitism, as articial light may locally
concentrate prey and effectively extend photoperiods, poten-
tially beneting otherwise diurnal parasitoids and predators.
Bottom-up effects via hostplants
Night-time lighting can affect plants through a range of physio-
logical and ecological mechanisms, though the topic has received
relatively little attention (for reviews, see: Briggs, 2006; Bennie
et al., 2016; Singhal et al., 2019).
Articial light can modify the quantity of hostplants available
for herbivores. For instance, mesocosm experiments have
revealed negative bottom-up effects on aphid abundance due to
reduced plant biomass and/or owering under LED lighting
(Sanders et al., 2015; Bennie et al., 2018b). Anthropogenic light-
ing can also change the quality of hostplants. For instance, car-
bon/nitrogen ratios in plants can be affected by lighting, with
knock-on effects for herbivores (Vänninen et al., 2010; Barber &
Marquis, 2011; Bennie et al., 2018b). Indirect effects on moth
larvae due to ALAN altering the biochemistry of foodplants
remain untested. However, negative developmental effects from
HPS lighting have been found in A. sordens caterpillars, which
appear to result from the hostplant being physically tougher, so
less digestible, under lit conditions (Grenis & Murphy, 2019).
Outdoor lighting can also alter plant phenology, for instance,
causing early budburst in deciduous trees (Ffrench-Constant
et al., 2016). This could result in phenological mismatch if moth
ova use non-photic cues (e.g. temperature) and therefore hatch
after budburst. By this time, leaves can be too rich in phenols
and tannins to be easily digestible by caterpillars
(Feeny, 1970). Articial light can alter the phenology of, or even
suppress, owering in some plants (Whitman et al., 1998; Chen
et al., 2009; Vänninen et al., 2010; Bennie et al., 2018a). This
could potentially impact upon moth larvae that consume owers
and seeds (Pettersson, 1991), as well as creating a mismatch
between the phenology of ower-visiting adults and their nectar
sources (Petanidou et al., 2014; Macgregor et al., 2015).
Top-down effects mediated by parasitoids and predators
Parasitoids can exert strong indirect effects on moths, as these
typically cause the death of the host (either at the egg, larval or
pupal stage). Night lighting may be predicted to affect parasitoid
behaviour and populations in various ways. The potential for
ALAN to cause elevated rates of parasitism in insects has already
been demonstrated. Low levels of LED lighting (0.15 lux) in a
eld experiment doubled the parasitism rate of an aphid, relative
to unlit controls (Sanders et al., 2018). The authors hypothesise
that the wasps predominately search for prey by day; thus, they
can exploit the night light nicheunder articial light. Parasitoid
wasps display positive phototaxis, so local densities could also
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
10 Douglas H. Boyes et al.
be boosted around outdoor lighting, leading to more parasitism.
Conversely, night lighting can suppress parasitism. Bright LED
light (10100 lux) causes decreased parasitism of aphids, possi-
bly because the wasps are drawn up towards lamps (Sanders
et al., 2018). Continuous night-time lighting might disrupt key
demographic processes of the parasitoids themselves (perhaps
via similar mechanisms to those described above for moths),
causing local densities to decline. Lighting could also disrupt
the synchronicity of the phenology of parasitoids and their hosts
if photoperiod is used as a cue for emergence. To date, no
research has been conducted on how night lighting affects para-
sitism rates in moths. The existence of hyper-parasitoids makes
these indirect effects even more difcult to predict.
Bat predation of adult moths is commonly observed around street
lights (Frank, 1988; Rydell, 2006). Some species of bat exploit the
high prey densities gathered around lamps (Rydell, 1992; Minnaar
et al., 2015; Russo et al., 2019). Furthermore, moths can fail to per-
form their usual anti-predation behaviours (e.g. evasive manoeu-
vres) in lit areas, rendering them even more susceptible to
predation (Svensson & Rydell, 1998; Acharya & Fenton, 1999;
Wakeeld et al., 2015). The elevated rates of bat predation around
outdoor lighting might deplete local moth populations.
Birds represent important predators of both adults and larvae;
however, the effects of light pollution on moth predation by birds
have rarely been tested. Songbird activity can be altered by articial
lighting (Titulaer et al., 2012; Dominoni et al., 2014), potentially
resulting in a longer period suitable for foraging in lit areas. As
demonstrated by the famous example of Biston betularia Linnaeus
(Geometridae), adult moths can be highly vulnerable to bird preda-
tion if their crypsis is di srupted (Cook et al., 2012). Adults attracted
to articial lamps frequently remain in situ and may fail to show
cryptic behaviour the following day, where they are readily pre-
dated (e.g. Collins & Watson, 1983). If light traps are run fre-
quently in the same location, songbirds seem to learn that these
will produce a high density of prey on the surrounding ground
and vegetation at dawn (Randle, 2009). Yet, it is unknown whether
this type of bird predation occurs when the light is not near the
ground, for instance, around street lamps (where there are no prox-
imate surfaces for moths to settle on).
The abundance of predatory invertebrates can be intensied
around outdoor lighting (Davies et al., 2012; Mcmunn
et al., 2019). Certain spiders preferentially construct webs near light
sources (Heiling, 1999), while some diurnal species of jumping spi-
der utilise the night light nicheby hunting by lamps at night
(Frank, 2009). Social wasps (Vespula species) have been observed
feeding on adult moths attracted to light (Warren, 1990). However,
aeld experiment has demonstrated that live moth larvae pinned to
Styrofoam squares do not suffer higher rates of predation (predom-
inately from ants, wasps, and spiders) under street lights (Grenis
et al., 2015) and lit spider webs can have lower rates of adult moth
capture compared to unlit webs (Yuen & Bonebrake, 2017).
Mixed results from eld-based and correlative studies
on moth assemblages
Field-based studies, including both experimental and correlative
analysis of observation data, are important for determining
whether behavioural and physiological changes due to articial
light at the individual-level (often demonstrated in laboratories)
translate to population-level effects in the real world. Yet, eld
studies have generally provided mixed results on the effects of
articial light on moth assemblages.
An experimental study that installed LED street lights along
the forest edge at seven sites in the Netherlands, found no effect
on adult moth abundance after 1 year (Spoelstra et al., 2015). A
separate experiment as part of the same project found increased
arboreal caterpillar biomass over several years in response to
7.6 lux from green and white LEDs, relative to red LEDs and
dark controls (Welbers et al., 2017), which the authors suggest
resulted from adult moths being attracted to the lit areas. Con-
versely, in Hungary, caterpillar biomass was not correlated with
varying levels of articial light (predominately HPS lamps)
across 36 urban trees (Péter et al., 2020).
In a matched-pairs experiment, moth abundance at the ground
level was found to be 0.5 times lower under HPS lamps, com-
pared to unlit sites, while at the height of the light, ight activity
was 1.7 higher at lit sites (Macgregor et al., 2017). Lit sites also
had signicantly lower species richness than unlit sites. This pro-
vides evidence of a local disruption effect (Fig. 3), as opposed to
concentration or trap effects, whereby moths would be drawn in
from surrounding areas. In contrast, a before-after-control-
impact study found that a change from LPS to HPS street lights
led to increased species richness (Plummer et al., 2016), which
the authors attribute to moths being drawn in from surrounding
areas. However, this study had limited temporal replication and
was spatially pseudoreplicated.
In East Lansing (USA), macro-moth abundance and species
richness were not predicted by levels of light pollution across
32 urban sites (White, 2018), though this could be explained
by adaptation to ALAN by moths in urban areas. In the United
Kingdom, there was no detectable difference in long-term trends
of the abundance of macro-moths at sites that had witnessed an
increase in light pollution, compared with sites that had remained
dark (Conrad et al., 2006). Furthermore, if light pollution were
the main driver of moth declines, one would expect urban areas
to be most affected; however, since the early 1980s, moth bio-
mass in the United Kingdom has declined more steeply at wood-
land and grassland sites, compared to those in urban areas
(Macgregor et al., 2019b).
Two correlative studies have hinted at the importance of light
pollution for explaining population trends in European macro-
moths. In the Netherlands, diurnal moths show more positive
trends than nocturnal moths, and moths that are classed as not
attracted to light also tend to be faring better (van Langevelde
et al., 2018). Yet, the groups that showed a signicant difference
in trends contained only a small number of the 481 species tested
(23 classed as diurnal, and 20 grouped as not attracted to light).
Furthermore, diurnal moths could be faring better due to factors
not related to light pollution (e.g. climatic changes) and deter-
mining the extent to which nocturnal moths are attracted to light
is not straightforward. This was based on expert assessment in
the study and not measured quantitatively. In Great Britain, the
abundance ratio of certain species between gardens with low
and medium levels of light pollution was correlated with national
abundance trends (Wilson et al., 2018). Species that are
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 11
relatively less abundant in gardens with higher levels of light
pollution tended to have more strongly negative national trends.
In the Czech Republic, it has been noted that many endangered
Noctuidae are rare or absent from areas with higher light pollu-
tion (Tihelka, 2019). Whilst both studies made efforts to disen-
tangle the effects of urbanisation from light pollution, it is not
clear whether this was achieved successfully in either case. Iso-
lating the effects of ALAN from its confounding factors must
be a priority for researchers (Hopkins et al., 2018)
Articial light and pest moth populations
The purpose of this review is to document the unintentional
impacts on moths from ALAN; however, it is interesting to note
that in certain circumstances light has been intentionally used to
suppress moth populations. The mechanisms and life stages
involved are not always clear but may involve suppression of
adult activity, or perhaps interference with specic behaviours
linked to crop damage (e.g. oviposition). These control efforts
have typically employed bright illumination. The impact of
lower levels of ALAN (e.g. analogous to ecological light pollu-
tion) remains untested but might be expected to be small since
direct articial illumination of crops is not currently a common
control strategy for insect pests.
Illuminating crops in elds and orchards has been reported as
a method of controlling moth pests. In eld experiments, illumi-
nation of cotton elds by incandescent lamps (producing 50 lux
at crop height) reduced Heliothis oviposition by 85%
(Nemec, 1969). Illuminating orchards can signicantly reduce
the damage made by fruit-piercing adult moths (Nomura, 1965;
Whitehead & Rust, 1972; Bhumannavar & Viraktamath, 2013)
and this can also limit larval damage by C. pomonella
(Herms, 1929). Whilst such trials have often been effective at
reducing crop damage, they have used high intensities of light
and the associated energy expenditure typically outweigh any
yield benets (Herms, 1947). The desire to reduce pesticide
use and the efciency of LEDs may make constant illumination
of crops a more viable option in the future (Shimoda, 2018).
Conversely, it has been suggested that outdoor lighting could
increase pest outbreaks of Grapholita molesta (Busck; Tortrici-
dae), as this species undertakes key reproductive behaviours
between 3 and 500 lux (Li et al., 2019).
Lethal light traps have been trailed as a method to directly con-
trol populations, with mixed success (Herms, 1947;
Cantelo, 1974; Kim et al., 2019). Unless a high density of traps
is deployed over a large area, lethal light trapping might only
be expected to have an appreciable impact on the populations
of the least mobile species (Cantelo, 1974; Bowden, 1982; Vai-
sanen & Hublin, 1983).
Cascading effects and disruption of ecosystem
function
The potential impacts of ALAN on moth assemblages and popu-
lations could cascade to other taxa with which moths closely
interact. In moths, the ontogenetic niche change (Nakazawa,
2015), with herbivorous larvae (antagonistic) becoming pollinat-
ing adults (mutualistic), might have important consequences for
predicting the indirect effects of ALAN on plant community
dynamics. A third fundamental position occupied by moths
within ecological networks is as prey for predators and parasit-
oids (see section on indirect effects above). Despite the signi-
cant potential for cascading effects from moths due to light
pollution, few eld studies have investigated these, with most
focusing on pollination. The presence of HPS street lights in eld
margins is linked to lower rates of pollen transport in moths
(Macgregor et al., 2017). A eld experiment using LED lamps
found that lighting reduced nocturnal visits, with fewer species,
and reduced pollination success, compared to dark controls
(Knop et al., 2017). This provides eld-based evidence that moth
feeding behaviour can be disrupted by lighting, which is in con-
gruence with an earlier laboratory result (van Langevelde
et al., 2017). However, a similar eld study found the opposite
result: higher seed set under LED lighting (Macgregor
et al., 2019a), meaning that the impacts of ALAN on ower vis-
itation by moths and the consequent cascading impacts on plant
tness may be context specic.
It has been suggested that larger moths may be more sensitive
to light pollution, as they tend to be more strongly attracted to
light, likely due to larger eye size (van Langevelde et al., 2011)
and also perhaps because they are more mobile (and therefore
more likely to come into contact with lighting). This could lead
to disproportionate impacts on ecosystem functioning if larger
moths are particularly important, i.e. correlated effect and
response traits (Larsen et al., 2005).
Potential for adaptation in response to anthropogenic
light
There has been highly consistent periodicity in light levels
throughout evolutionary history, meaning there is signicant
potential for evolutionary change in response to anthropogenic
light (Swaddle et al., 2015). The short-term changes in phero-
mone composition and mating behaviour in moths due to arti-
cial light (van Geffen et al., 2015a, 2015b) raises the distinct
possibility of divergent selection, and potentially speciation, in
moths as a direct consequence of articial light at night
(Tierney et al., 2017). If outdoor lighting acts as a dispersal bar-
rier, this may cause effective population fragmentation, speeding
up rates of evolution (Degen et al., 2016).
The discovery that a species of micro-moth appears to have
evolved reduced phototaxis in certain urban areas (Altermatt &
Ebert, 2016) provides the rst evidence that moths have adapted
to anthropogenic light. In theory, this result could also mean
trend data from light traps in urban areas are unreliable, as pop-
ulation sizes might become detached from light trap catches.
Further work should be conducted to determine whether evolu-
tionary adaptation to light has also occurred in moths from other
geographical regions, and in other taxonomic families. The rapid
shifts in lighting technologies (e.g. switch from narrow to broad-
spectrum lamps) could mean that insects that have successfully
adapted to one lighting type are not adapted to others.
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
12 Douglas H. Boyes et al.
Insects in the arctic do not experience large cycles in the inten-
sity of light and daily activity is typically controlled by tempera-
ture (Downes, 1965; Danks, 2004). Species of moth that are
nocturnal in Denmark are able to persist successfully in Green-
land, where they appear to have acclimated to the radically dif-
ferent photic conditions (Dreisig, 1981). The process of
acclimation and/or adaptation involved is not clear, nor is it
known how rapidly insects can respond to altered photic
regimes, but these ndings do suggest that some moths that are
nocturnal at lower latitudes can survive in the absence of dark
nights. There is evidence that other Arctic fauna entrain their cir-
cadian rhythm using diel shifts in the spectral composition of
light, instead of changing intensity (Krüll et al., 1985; Nordtug &
Mela, 1988).
Mitigation of the disruptive effects of outdoor lighting
Finding ways to mitigate the ecological impacts of ALAN is an
interdisciplinary challenge. Outdoor lighting carries numerous
societal benets, such as preventing trafc collisions
(Wanvik, 2009; Yannis et al., 2013), reducing crime (Welsh &
Farrington, 2008) and increasing perceived public safety, partic-
ularly for marginalised groups (Trench et al., 1992;
Painter, 1996). Conversely, concerns about the impacts of light
pollution on astronomy (Riegel, 1973) and human health (Cho
et al., 2015) mean that reducing light pollution has the potential
to deliver a winwin for both biodiversity and people.
A raft of mitigation measures has been advocated for outdoor
lighting, many of which are relatively easy to implement, such as
turning off or dimming lights for part of the night, and adding
shielding to street lights to restrict the area illuminated (Gaston
et al., 2012; Davies & Smyth, 2018). It is generally thought that
broader spectrum lighting (e.g. LEDs) has the potential for
greater ecological impacts than narrow-spectrum lighting
(e.g. LPS), as the wider range of wavelengths emitted can affect
a greater range of taxa and biological processes (Davies
et al., 2013; Longcore et al., 2018). The energy efciency of
LEDs means that it is unlikely that older lamp technologies will
be retained, so adjusting the spectral composition of LEDs to
reduce the intensity of the most biologically disruptive wave-
lengths, while still maintaining the benets to people, could be
a more feasible mitigation strategy (Gaston et al., 2012). Whilst
no difference has been detected in the number of moths attracted
to LEDs of varying spectral proles (Pawson & Bader, 2014;
Supporting Information Fig. S2), longer wavelengths (red
LEDs) have been shown to partially mitigate the negative
impacts on key behaviours in moths to varying degrees (van Gef-
fen et al., 2014, 2015a,b).
Understanding which wavelengths of light moths are sensitive
to may be crucial for designing successful mitigation strategies.
The eyes of nocturnal moths typically have three maxima in their
sensitivity; for instance, Deilephila elpenor (Linnaeus; Sphingi-
dae), has photoreceptors with peak sensitivities in the ultraviolet
(350 nm), violet (440 nm), and green (525 nm) regions
(Schwemer & Paulsen, 1973; Schlecht, 1979). These visual sen-
sitivities have been compared to spectral outputs to predict the
ecological impacts of different street light technologies (Davies
et al., 2013; Longcore et al., 2018; Seymoure et al., 2019).
Yet, adult moths also possess extraocular photoreceptors, includ-
ing in the brain and reproductive organs (Page, 1982; Giebulto-
wicz et al., 1989). The perception of photoperiod appears to
rely on extraocular receptors in some adult moths (Saunders,
2008). Transplant experiments have revealed that photorecep-
tors in the brain are responsible for diapause regulation in the lar-
vae of a hawkmoth and silkmoth (Bowen et al., 1984;
Hasegawa & Shimizu, 1987), and it is thought that red wave-
lengths of light are most important for the regulation of diapause
(Saunders, 2012). Thus, the disruption of certain biological pro-
cesses (e.g. those related to circadian rhythm) by articial light
will not necessarily correspond to the visual sensitivity of moths
and wavelengths of light that moths are visually insensitive to
could still be harmful.
Elucidating the mechanisms by which lighting could disturb
moth populations is also likely to be important for designing
effective mitigation measures. For instance, if negative effects
occur from moths incorrectly perceiving longer photoperiods
in lit areas, then turning off the lamps part way through the night
may be equally harmful, as the perceived photoperiod remains
articially extended. Conversely, if disrupted adult behaviour
around lamps is a signicant factor, then part-night lighting
might be effective in enabling key behaviours to proceed for
some of the night. This may be taxon-specic, as different spe-
cies y at different times of the night (Williams, 1939), with cre-
puscular groups (e.g. Hepialidae) potentially receiving little
benet, compared to species that y later in the night.
Conclusions and future directions
We have detailed the multitude of mechanisms by which arti-
cial lighting could impact moth populations and how it poten-
tially acts on every stage of the life cycle (Fig. 2). However,
we conclude from our detailed review that, as yet, there is limited
evidence that light pollution is exerting negative effects at the
population level. We believe that some studies have prematurely
attributed insect declines to ALAN (e.g. Owens et al., 2020),
although we acknowledge that the lack of direct evidence could
reect the relatively small number of studies that have examined
changes to moth assemblages or population trends in the context
of ALAN (to date, 11 studies, as discussed above). This paucity
of direct evidence could also reect the challenges in detecting
causal effects. We therefore advocate that the precautionary prin-
ciple is invoked and emphasise the need for further research into
this topic. Crucially, there is a need to consider the effects of light
pollution in the context of other drivers of change, such as agri-
cultural intensication and climate change (Fox, 2013); does
light pollution represent a major threat, or is its contribution
effectively negligible when placed in the context of other anthro-
pogenic drivers?
Commonly, studies have taken the number of adult insects
attracted to a light source as a proxy for its ecological impact
(e.g. Pawson & Bader, 2014; Wakeeld et al., 2018; van Gruns-
ven et al., 2019). Results of our meta-analysis mean that historic
trends in street lighting technology might be predicted to have
benetted moths. Mercury-vapour lighting elicits among the
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 13
strongest phototactic response in moths and was commonly used
in the United Kingdom during the middle of the 20th century,
before being replaced by sodium street lights (McNeill, 1999).
Moths are thought to be largely insensitive to low-pressure sodium
lamps, so the switch to high-pressure sodium lamps possibly had
negative impacts, whilst the ongoing switch from high-pressure
sodium to LED lighting is likely to have a minimal, or even posi-
tive, effect on moths (in terms of ight-to-light behaviour; Fig. 2).
Yet, we are unconvinced that the attractiveness of a light source
serves as a suitable proxy for ecological impact, given the many
Fig. 4. Potential effects of articial light on moths, grouped by the mode of mechanism. The life stages that could be affected are indicated. [Color gure
can be viewed at wileyonlinelibrary.com]
(a)
(c)
(b)
(d)
Distance
Local
abundance
Fig. 5. Hypothesised relationships between local moth abundance and distance from a light source (bulb). Dotted horizontal line show moth abundance
in the absence of light. The blue solid line is the hypothesised moth abundance. Filled downward arrows represent local depression of abundance due to
light. Hollow sideways arrows show movement due to phototaxis. (a) Abundance suppressed locally due to light (negligible population-level effect).
(b) Concentration effect, where abundance boosted around light due to moths being drawn in from surrounding areas, which are consequently slightly
depleted (no population-level effect). (c) Strong local depression, combined with moths being drawn from surrounding areas (moderate population-level
effect). (d) A large proportion of landscape directly lit, with concentration effects, causing overall population level to be suppressed (high population-level
effect). [Color gure can be viewed at wileyonlinelibrary.com]
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
14 Douglas H. Boyes et al.
ways that anthropogenic light can affect moths (Figure 1) and cau-
tion against making policy recommendations from data that only
examine one narrow impact on a single life stage.
It can be valuable to group the effects of ALAN within a mech-
anistic framework (Gaston et al., 2013). For moths, the impacts
of ALAN can be broadly categorised into four modes of action:
light perceived as daylight, light eliciting phototaxis, light inter-
fering with celestial cues, and light causing direct damage or pre-
venting dark repair (Fig. 4). We consider that the rst two modes
of action as having the greatest potential for harm to moths.
It is important to consider the scale over which the mecha-
nisms discussed above operate. The proportion of landscapes
that are directly lit by anthropogenic lighting is typically rela-
tively small. While diffuse skyglow covers a much greater area,
there is currently no evidence that such low levels of articial
light affect moths. If direct illumination does exert strong nega-
tive local effects on moths, this could still be negligible at
population-level (Fig. 5a), unless: (i) a high proportion of the
landscape is directly lit (Fig. 5d); (ii) moths are drawn in from
a wide radius, depleting surrounding populations (Fig. 5c;
Fig. 3); and/or (iii) a species has limited dispersal.
Whilst moths were the focus of this review, we consider it
likely that our ndings and conclusions are broadly applicable
to most other groups of insects. Importantly, since the majority
of the mechanisms discussed above do not involve adult photo-
taxis (Figs. 1 and 4), then there is the potential for diurnal insects
(i.e. those active in the day in their adult stage, such as butter-
ies) to be negatively impacted by light pollution, for instance,
through disruption of the circadian rhythm, or via a nocturnal lar-
val stage.
Priorities for future research
Our review has revealed gaps in our understanding of
how articial light might affect moth populations (Table 2).
Despite most moths only living as an adult for a small
fraction of their lifespan, relatively few studies have investigated
impacts on earlier life stages. Much of the work has been con-
ducted on a small number of moth species (often of commercial
importance).
Some of the laboratory studies discussed were not investigating
light pollution, thus did not use conditions analogous to outdoor
night lighting. For instance, continuous lighting in laboratory cul-
tures typically remains unchanged over 24-hr periods. Yet, even
the brightest articial lighting will not completely mask the diel
cycle in this way. As a result, there is a need for more experiments
to use photic conditions that may be experienced under street light-
ing (e.g. van Geffen et al., 2015a) to clarify whether the mecha-
nisms involving an entrained circadian rhythm (e.g. sperm
release) are affected by low levels of articial light at night. Low
levels of LED lighting can affect two processes controlled by pho-
toperiod in M. brassicae: diapause in larvae and pheromone pro-
duction in adults (van Geffen et al., 2014, 2015b); therefore,
bright light at night may not be necessary to disrupt processes
dependent on circadian rhythm in moths.
The increasing extent and intensity of ALAN mean there is an
urgent need for more well-replicated eld studies to determine
whether the disruptive effects demonstrated in behavioural stud-
ies (often with single species), scale up to real-world networks of
interacting species under eld-realistic levels of lighting. Ulti-
mately, the relative contributions of individual anthropogenic
factors, including light pollution, needs to be teased apart from
the complex interplay of drivers that are likely to be implicated
in the decline of European moths.
Acknowledgements
This work was funded by the Natural Environment Research
Council (reference: NE/L002590/1) and Buttery Conservation
(industrial CASE studentship awarded to D.H.B., IAPETUS
DTP). The authors are grateful to Roy van Grunsven, Peter Hue-
mer, Martin Soneira, and Silvana Poiani for responding to data
requests for our meta-analyses. The authors thank Dirk Sanders
and an anonymous reviewer for their constructive comments
on an earlier version of this manuscript.
Data availability statement
Data available in article supplementary material
Table 2. Outstanding research questions raised by this review.
Direct mechanisms
Over what scales are moths drawn in to (and affected by) lit areas? Do
urban areas represent ecological traps for moths?
What are the rates of mortality of moths attracted to street lamps?
Do some moths exhibit negative phototaxis and actively avoid lit areas
at night?
Are circadian processes (e.g. sperm release) routinely disrupted by
intensities of light typically experienced by moths outdoors at night?
How does outdoor lighting affect oviposition?
Is the activity of nocturnal moth larvae suppressed by anthropogenic
light?
Can very low levels of diffuse light pollution (skyglow) exert
negative effects on moths?
Indirect effects
Does light pollution affect rates of parasitism in moths?
Is bird predation, of adults or larvae, elevated in lit areas?
Is larval development in lit areas affected by biochemical changes that
occur in foodplants?
Does articial light engender phenological mismatch between plants
and moths (either hostplants and larvae, or owers and nectar-reliant
adults)?
Population-level effects, evolutionary responses, and mitigation
Do behavioural effects and evidence of local disruption, scale up to
population-level impacts?
What proportion of moth declines can be attributed to light pollution,
relative to other drivers (e.g. climate change, agricultural
intensication)?
Does articial lighting interact with other drivers (e.g. warming due to
climate change or urban heat effects)?
Are evolutionary changes in response to ALAN widespread across
moth species?
Can policy interventions be effective in delivering win-wins by
maintaining benets to people while minimising disruptive impacts
on insects?
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 15
Supporting information
Additional supporting information may be found online in the
Supporting Information section at the end of the article.
Appendix S1: Methods used for network meta-analyses of
ight-to-light responses to different light types.
Appendix S2: Studies located for the meta-analyses.
Appendix S3: Treatment estimates used in the meta-analyses.
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Accepted 25 August 2020
Editor: Alan Stewart; Associate Editor: Nick Littlewood
© 2020 The Authors. Insect Conservation and Diversity published by John Wiley & Sons Ltd on behalf of Royal Entomological
Society., Insect Conservation and Diversity, doi: 10.1111/icad.12447
Light pollution and moth life cycles 21
... Entre los impactos biológicos mejor documentados se incluyen cambios en la fenología, la predación, la reproducción, la capacidad de orientación y migración, el comportamiento, la comunicación y la fisiología de los organismos (Longcore & Rich, 2004;Seymoure, 2018). Aunque no hay todavía un consenso sobre la magnitud del impacto negativo del ALAN sobre las especies en términos poblacionales (Boyes et al., 2020), cada vez son más los estudios que sugieren que éste podría ser alto Grunsven et al., 2020). Así por ejemplo, Owens y colaboradores (2020) no dudan en señalar al ALAN como unas de las principales causas de la rápida regresión observada en los insectos a escala global durante las últimas décadas. ...
... En concreto, el ALAN puede generar interferencias en funciones básicas tales como la alimentación y la reproducción (van Langevelde et al., 2017). Estas interferencias están bien documentadas en, al menos, los nóctuidos, uno de los grupos más abundantes y diversos (Boyes et al. 2020). Aunque el grado de atracción hacia la luz puede variar entre las familias de los macrolepidópteros (Merckx & Slade, 2014) e incluso entre especies y ejemplares de diferente sexo, la mayoría de las especies muestran dicho comportamiento (Eisenbeis, 2006) y son, por tanto, susceptibles de sufrir los impactos del ALAN. ...
... Los resultados indican que el tipo de lámpara utilizado para el alumbrado callejero de núcleos rurales del Pirineo occidental puede jugar un papel clave en la conservación en las poblaciones locales de macrolepidópteros. Un estudio reciente ha demostrado que existe una alta correlación entre las capturas de polillas y el resto de insectos nocturnos (al menos de aquellos con fototaxis; Boyes et al., 2020). Por tanto, los resultados de este estudio podrían ser generalizables en buena medida al conjunto de los insectos voladores nocturnos. ...
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Testar el grado de atracción que ejercen las lámparas de VM, HMC, VSAP, LED blanco y LED PC-Ámbar sobre las comunidades de macrolepidópteros nocturnos del Pirineo occidental (Navarra). 2. Desgranar el efecto de los diferentes tipos de lámparas a nivel de familia y analizar el efecto de atracción/repulsión ejercido sobre las especies más abundantes y comunes. 3. Evaluar la atracción ejercida por los tipos de lámparas sobre las especies de macrolepidópteros de interés comunitario G. isabellae y P. proserpina.
... Many behavioural responses of insects to artificial light sources have been documented anecdotally and experimentally (for a review, see [48]). Most recently, reconstructions of flight kinematics have shown that insects orient their dorsum to the light, which, under unnatural conditions, results in continuous flight towards and around the light [28]. ...
... The nature of vehicle headlights as horizontally focused beams means they create linearly polarized reflections from the flat road surface (particularly when wet [55]). Moths are able to see polarized light [56], and it remains to be determined how polarization and pALAN might interact [48,55,56]. Behavioural work would also benefit from more realistic headlight simulations, with moving lights that gradually increase in brightness, combined with modelling the likelihood of moths being impacted by vehicles. ...
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Vehicle headlights create pulsed artificial light at night (pALAN) that is unpredictable, intense and extends into previously dark areas. Nocturnal insects often have remarkable low-light vision, but their slow pupillary light responses may leave them vulnerable to pALAN, which has important ecological consequences. To test this, we exposed nocturnal moths—important pollinators and prey—to four pALAN treatments. These comprised ‘cool’ and ‘warm’ lights, either emitted from phosphor-coated light-emitting diodes (LEDs) or RGB (red-green-blue) LEDs, matched in colour (CCT) and intensity to human vision. We assessed the initial behavioural response, likely crucial to the survival of an organism, of 428 wild-caught moths comprising 64 species. We found that exposure to a cool phosphor-coated LED light pulse increased instances of erratic flight and flight-to-light that are likely detrimental as they increase the risks of impact with a vehicle, predation or excess energy expenditure. Our findings suggest that pALAN can cause a wide range of behavioural responses in nocturnal moths, but that the most harmful effects could be minimized by reversing the current shift towards high CCT (cool) phosphor-coated LED car headlights. Lower CCT or RGB alternatives are likely to provide benefits for road safety while reducing ecological harm.
... U ne expérimentation originale a permis d'étudier, sur site réel, l'effet de l'ALAN sur les population de papillons de nuit (Boyes et al., 2021a), dans un contexte où les populations d'insectes sont en déclin (Grubisic et al., 2018;Owens and Lewis, 2018;Owens et al., 2020;Boyes et al., 2021b). En particulier, l'impact de l'ALAN sur la pollinisation est discuté (Knop et al., 2017). ...
... Pour les auteurs, ce résultat vient du fait que leur protocole tient compte d'effets à long terme, puisque l'éclairage est installé depuis des années. De plus, leurs résultats semblent infirmer les hypothèses habituellement admises selon lesquelles il y a une corrélation entre la capacité d'attraction des sources et l'abondance des espèces (Pawson and Bader, 2014;Boyes et al., 2021b). D'autres mécanismes doivent donc être recherchés, comme par exemple un effet sur la ponte des oeufs, ou des effets indirects mettant en jeu la nourriture des chenilles ou les prédateurs. ...
Technical Report
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Notes de lecture: éclairage et biodiversité. Lecture notes: lighting and biodiversity.
... More than 60% of invertebrates are estimated to be nocturnal [82], including 75-85% of Lepidoptera [83]. Flying nocturnal insects often show flight-to-light behavior like many moths [84] and are hence attracted to light. Since the sampling design of Hallmann et al. [14] focused on flying insects, increasing ALAN intensities over time could have been partially responsible for reducing sampled insect biomass, since nocturnal flying insects are potentially confused, deterred, or lured depending on their behavior [80]. ...
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The decline of insects is a global concern, yet identifying the factors behind it remains challenging due to the complexity of potential drivers and underlying processes, and the lack of quantitative historical data on insect populations. This study assesses 92 potential drivers of insect decline in West Germany, where significant declines have been observed. Using data from federal statistical offices and market surveys, the study traces changes in landscape structure and agricultural practices over 33 years. Over the years, the region underwent major landscape changes, including reduced cropland and grassland and increased urbanization and forest areas. Potential detected drivers of insect decline include: (1) urban expansion, reducing insect habitats as urban areas increased by 25%; (2) intensified grassland management; (3) shifts in arable land use towards bioenergy and feed crop cultivation, particularly corn, driven by dairy farming intensification and renewable energy policies. While the toxic load of pesticide application has decreased, land-use changes, most likely driven by market demands and shifts in national and EU policies, have reduced habitat availability and suitability for insects. This study highlights how these landscape and land management changes over the past 33 years align with the observed decline in insect biomass in the region.
... Unlike incandescent lamps, which emit light in all directions and consume more energy to produce the same amount of light, LED lamps are more efficient and can be designed to minimize light dispersion. This results in a significant reduction in ALAN, especially in urban and coastal areas where artificial light sources are more intense [80,84]. ...
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This study investigates the impact of artificial light at night (ALAN) along the Sicilian coasts, using satellite data from 2016 to 2023, focusing on three distinct spatial domains: terrestrial areas within 1 km from the coastline, marine areas extending up to 1 km offshore, and marine areas up to 1 nautical mile from the coast. In coastal zones, ALAN is a significant anthropogenic pressure with potentially detrimental effects on ecosystems. By integrating satellite data with geographic datasets such as Corine Land Cover (CLC), Natura 2000 protected areas, and Posidonia oceanica meadows, this study aims to characterize and analyse the temporal and spatial variations in ALAN across these domains. The findings reveal substantial differences in light pollution between domains and over time, with coastal terrestrial areas exhibiting the highest levels of ALAN. In contrast, marine areas further offshore experience reduced light pollution, particularly within the 1-nautical-mile domain. This study also indicates that protected areas, especially those within the Natura 2000 network, show significantly lower ALAN levels than non-protected areas, highlighting the effectiveness of conservation efforts. Statistical analyses, including ANOVAs, demonstrate that factors such as geographic domain, year, province, and CLC classes significantly influence ALAN distribution. This study advocates for considering ALAN as a critical factor in environmental impact assessments, such as those under the Maritime Spatial Planning Directive (MSP) and Marine Strategy Framework Directive (MSFD), providing valuable insights to support policies aimed at mitigating the environmental impact of light pollution on coastal and marine ecosystems.
Preprint
1. The addition of nectar-rich flower patches in human-modified ecosystems is a common practice to mitigate pollinator declines and boost pollination. However, the benefits of these additions for pollinator communities and pollination services are rarely tested, especially in urban environments. 2. In a city-scale experiment we added floral resources to urban allotments and monitored the effects on bees, hoverflies and moths, and tested for improved seed set in a model crop (tomato, Solanum lycopersicum). 3. The addition of wildflowers did not benefit all insect communities. Only social bee abundance (Bombus and Apis) benefitted from increasing floral resource area whereas other insect taxa showed no changes in abundance potentially due to the divergence in foraging patterns of moths, hoverflies, social bees and solitary bees. The addition of wildflower patches enhanced pollination by supporting a 25.3% increase in tomato seed set, providing evidence that wildflower interventions can improve urban pollination. Seed set was higher in more urban sites, suggesting an 'oasis effect' where pollinating insects are concentrated into limited greenspaces. This highlights the precarity of pollination services in highly urban areas. 4. Our results suggest that the practice of planting wildflower patches can positively affect pollination services in urban areas. The continued promotion of flower patch addition is likely to benefit some key insect taxa, however, the common wildflower species in seed mixes may not benefit hoverflies and moths compared to bees. The taxon-specific foraging patterns we observed should inform the design and development of pollinator-friendly wildflower seed mixes.
Technical Report
This is the Mission Description Document (MDD) for a future Earth observation satellite mission addressing visible band observations of nighttime lights. The mission driving science applications are for the remote sensing of electricity, energy, and ecological impacts via the observation of artificial light. The MDD covers the mission requirements justification from the high-level scientific objectives and societal benefits to measurement requirements at product level 1b, i.e. radiances at the top of the atmosphere. In providing justification for the individual requirements and their traceability to scientific objectives and societal challenges, we address Scientific Readiness Levels 1 to 3. The MDD is the outcome of the European Space Agency New Earth Observation Mission Ideas project "Night Watch". The Task Reports (TR) from the project are appended to the MDD, and are authored by the same group as the MDD itself.
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Agriculture driven land-use change is a major contributor to insect declines globally. As a result of population decline and subdivision, species lose genetic diversity, potentially reducing adaptive potential and increasing genetic load, reinforcing decline. We examine how genetic diversity has changed over the past century in three Polyommatinae (Lepidoptera: Lycaenidae) butterfly species in southern Sweden, leveraging genome sequencing of specimens from museum collections. Based on 63 historical and 92 contemporary genomes, we document a general decline in genetic diversity and reveal that the extent of decline depends on habitat specialization. The habitat generalist has retained most of its genetic diversity and connectivity. In contrast, the two specialists have declined sufficiently that even common variation is being eroded by drift, with up to a 3.3% reduction in heterozygosity per decade in the strongly grassland associated Cyaniris semiargus . While this sharp decline has reduced total genetic load in the two specialist species, increased population isolation has led to inbreeding in Cy. semiargus , exposing a greater proportion of load in homozygous state. This realized load likely reduces mean fitness and reinforces population decline, highlighting the need for well-connected grassland landscapes to maintain grassland specialist functional connectivity and genetic diversity. We complement these analyses with data on seven additional Polyommatinae species, uncovering that declines are common across the group, with alarming rates of genetic decline in species listed as viable. This study highlights the urgency of incorporating genetic data into conservation planning, as threats from genetic erosion are not captured by current conservation assessment.
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One of the most dramatic changes occurring on our planet is the ever-increasing extensive use of artificial light at night, which drastically altered the environment to which nocturnal animals are adapted. Such light pollution has been identified as a driver in the dramatic insect decline of the past years. One nocturnal species group experiencing marked declines are moths, which play a key role in food webs and ecosystem services such as plant pollination. Moths can be easily monitored within the illuminated area of a streetlight, where they typically exhibit disoriented behavior. Yet, little is known about their behavior beyond the illuminated area. Harmonic radar tracking enabled us to close this knowledge gap. We found a significant change in flight behavior beyond the illuminated area of a streetlight. A detailed analysis of the recorded trajectories revealed a barrier effect of streetlights on lappet moths whenever the moon was not available as a natural celestial cue. Furthermore, streetlights increased the tortuosity of flights for both hawk moths and lappet moths. Surprisingly, we had to reject our fundamental hypothesis that most individuals would fly toward a streetlight. Instead, this was true for only 4% of the tested individuals, indicating that the impact of light pollution might be more severe than assumed to date. Our results provide experimental evidence for the fragmentation of landscapes by streetlights and demonstrate that light pollution affects movement patterns of moths beyond what was previously assumed, potentially affecting their reproductive success and hampering a vital ecosystem service.
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Full-text available
Alternation of day and night is the oldest cycle on Earth, which is increasingly disturbed by the accelerating rate of urbanization and technological development. Despite the ubiquity of light pollution in cities, many aspects of its influence on urban ecosystems are still poorly understood. Here we studied the effect of artificial light at night (ALAN) on the biomass of arboreal caterpillar populations, which are a major component of the diet of many insectivorous animals. We predicted that increasing ALAN intensity is associated with reduced caterpillar biomass, because ALAN may increase predation risk for both caterpillars and adult lepidopterans (i.e. moths), and can also hinder the moths’ reproductive rate. We estimated caterpillar biomass from frass samples (n = 3061) collected from 36 focal trees in two cities in Hungary during four consecutive years. To quantify ALAN we measured light intensity during night at each focal tree (range of illumination: 0.69–3.18 lx). We found that caterpillar biomass of individual trees was repeatable over the four years. This temporal consistency in prey biomass production may be important for birds because it can help predict territory quality, especially in cities where caterpillar abundance is generally low. Our results did not support the negative effect of ALAN on urban caterpillar populations, because ALAN intensity was not related to caterpillar biomass, and this lack of effect was consistent between study sites and tree species. We suggest that the effect of ALAN on urban caterpillar biomass is either weak and thus can be masked by other, local environmental factors, or light pollution may have antagonistic effects acting during different stages of the lepidopteran life cycle. Another explanation could be that even the lower levels of our sites’ public lighting are strong enough to cause serious detrimental effects for caterpillars, resulting in their uniformly low biomass.
Article
Full-text available
Among the different light sources used for street lighting, light-emitting diodes (LEDs) are likely to dominate the world market in the coming years. At the same time, the spectral composition of nocturnal illumination is changing. Europe and many other areas worldwide have implemented bans on energy-inefficient lamps, such as the still very common mercury vapor lamps. However, the impact of artificial light on insects is mostly tested with light-traps or flight-intercept traps that are used for short periods only. By comparing the numbers of insects attracted by street lamps before and after replacing mercury vapor light sources (MV) with light emitting diodes, we assessed the impact in more typical (urban and peri-urban) settings over several years. We found that LED attracted approximately half of the number of insects compared to MV lights. Furthermore, most insect groups are less drawn by LED than by MV, while Hymenoptera are less attracted by MV than by LED. Thus, the composition of the attracted communities differed between the light sources, which may impact ecosystem processes and functions. In green peri-urban settings more insects are attracted than in an urban setting, but the relative difference between the light sources is the same.
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Data from Butterfly Conservation's National Moth Recording Scheme and the MothsIreland database have been combined to produce the first-ever atlas covering all larger moths in Britain, Ireland, the Isle of Man and the Channel Islands. It includes distribution maps showing current and historical records for 893 species and up-to-date information on status, trends and phenology.
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