The effect of temperature and humidity changes on insects development their impact on forest ecosystems in the expected climate change

Abstract

Ongoing climate change is mainly evident as increased in average temperature. It is expected to have a significant impact on world’s biomes, with forest ecosystems especially vulnerable to these changes. The effect of climate change on forests is both indirect, through its impact on various tree species of different ecological requirements, and direct, through its impact on all living components of the forest ecosystem. Among the latter, insects are the group of the greatest importance, including species detrimental to forest health. The impact of climate change on forest insects may be reflected in their distribution, phenology, activity, number of generations and, indirectly, through impact on their natural enemies. Predicting the future direction and pace of the climate change, as well as direct and indirect consequences of its effect on forest insects is difficult and often subject to considerable inaccuracy. The paper presents a review of data from the published literature in this area of study. The influence of the basic climate parameters, temperature and humidity, on forest herbivore insects is discussed, particularly in the context of the most probable scenarios of climate change, i.e. the gradual increase in the average temperature. Observed and projected impacts of climate change in relation to the influence of herbivorous insects on forest ecosystems are characterized. We present some of the possible adaptation strategies of forest management to the expected climate changes.

Full text

REVIEW ARTICLE
DOI: 10.2478/frp-2013-0033 Leśne Prace Badawcze (Forest Research Papers),
December 2013, Vol. 74 (4): 345–355.
Received 24 June 2013, accepted after revision 19 Septembert 2013.
© 2013, Forest Research Institute
The effect of temperature and humidity changes on insects development their impact
on forest ecosystems in the expected climate change
Tomasz Jaworski *, Jacek Hilszczański
Forest Research Institute, Department of Forest Protection, Sękocin Stary, ul. Braci Leśnej 3, 05–090 Raszyn, Poland.
* Tel. +48 22 7150549, e-mail: T.Jaworski@ibles.waw.pl
Abstract. Ongoing climate change is mainly evident as increased in average temperature. It is expected to have
a signicant impact on world’s biomes, with forest ecosystems especially vulnerable to these changes. The effect
of climate change on forests is both indirect, through its impact on various tree species of different ecological
requirements, and direct, through its impact on all living components of the forest ecosystem. Among the latter, insects
are the group of the greatest importance, including species detrimental to forest health. The impact of climate change
on forest insects may be reected in their distribution, phenology, activity, number of generations and, indirectly,
through impact on their natural enemies. Predicting the future direction and pace of the climate change, as well as
direct and indirect consequences of its effect on forest insects is difcult and often subject to considerable inaccuracy.
The paper presents a review of data from the published literature in this area of study. The inuence of the basic climate
parameters, temperature and humidity, on forest herbivore insects is discussed, particularly in the context of the most
probable scenarios of climate change, i.e. the gradual increase in the average temperature. Observed and projected
impacts of climate change in relation to the inuence of herbivorous insects on forest ecosystems are characterized.
We present some of the possible adaptation strategies of forest management to the expected climate changes.
Key words: global warming, forest insects, population dynamics, forest insects’ outbreaks, range shift, phenology,
forest management
1. Introduction
Climate changes have signicant impact on natural
environment, regardless of their primordial cause. They
also inuence forest ecosystems. On the one hand,
alternated basic climate parameters affect individual tree
species of different ecological requirements directly, on
the other hand, it affects all other living components
of the forest ecosystem. Among the latter, insects are
the group of the greatest importance, including species
detrimental to forest health with regard to forest
management.
Insects belong to an ectothermic group of animals;
thus, they are highly dependent on thermal conditions
of the surrounding environment. Hence, besides food
plants, climate conditions are basic factors that form
insect range. Any climate changes are not neutral for
insects’ assemblages. The impact of climate change on
forest insects may be reected, e.g. by affecting their
range, phenology, activity, number of generations and
winter survival. Among the present theories of climate
changes, average temperature increase theory dominates
(IPCC 2007). Most of the several dozens of predictive
models indicate that average temperature can increase
by 1.7–5.3°C, as a result of doubling CO2 concentration
within next 60–100 years. 2.3°C is a value most often
mentioned what means an increase by 0.3°C a decade.
As opposed to temperature, humidity is characterised
by higher variability. It is difcult to indicate a distinct
trend within humidity as it is with regard to temperature.
By average temperature increase, atmospheric
precipitation increase in the middle and the northern
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on forest ecosystems in the context of expected climate change
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parts of the Northern Hemisphere is predicted. Apart
from that, it is assumed that water shortage will intensify
in the temperate zone in result of temperature increase
that will cause increase in evaporation. Soil will dry up
due to the result of varied factors: time reduction of the
snow retention, high saturation of surface soil at the end
of the winter and an accelerated surface water drainage
(Sadowski 1996, Chmura et al. 2010).
In the opinion of many researchers, predicted climate
changes will have an adverse inuence on forests
(Wigley 1993; Ayres, Lombardero 2000; Battisti 2008;
Moore, Allard 2008). For instance, increase in res and
adverse weather phenomenon (i.a. oods and hurricanes)
is predicted. In effect, a negative inuence of secondary
pests will accelerate (Sadowski 1996; Logan et al.
2003). Tree species of narrow ecological tolerance (for
instance, spruce and r) will retreat in Europe in favour
of species of a broad ecological optima (for instance,
poplar and alder) what involves a structural change in
dominant herbivores (Ryszkowski et al. 1995). Northern
and southern range shift is predicted with regard to many
insect species towards higher altitude and elevation
(Pawłowski 1995; Parmesan 1996; Walther et al. 2002;
Parmesan, Yohe 2003; Menéndez 2007; Battisti 2008).
It involves a risk of expansion and adjustment of new,
sometimes dangerous pests. Many native herbivore
species can increase the annual generations’ number, as
well as they can increase their chances to survive the
winter, and in result, they can multiply the population
number (Ayres, Lombardero 2000; Battisti 2008;
Netherer, Schopf 2010). Climate changes can also affect
the activity of native pests’ species that previously had
no signicant role for forests (Tenow et al. 1999).
Future direction and pace of the climate change
as well as its direct and indirect effects are difcult to
predict. It is caused by time and space unpredictability
and variability of climate parameters, as well as by
varied ways of climate inuence on individual functional
groups of biocoenosis and, last but not least, by the
complexity level of the biocoenosis. However, it is also
essential to recognise the mechanism behind climate
inuence on individual ecosystem components and in
case of forest environment – on insects that are ecological
guilds of a great importance to forest ecosystem. This
paper is a review on selected literature regarding the
aforementioned problem. We discuss different ways of
inuence of the climate basic parameters – temperature
and humidity – on phytophagous insects, regarding
the most probable scenario of climate changes, i.e.
successive increase in the average temperature on Earth.
We discuss humidity inuence less, because of small
number of research and difculties with interpreting
results. By giving examples, we also characterise
predicted and observed effects of climate changes with
regard to the inuence of phytophagous insects on
forest ecosystem. Finally, we present several bearings
of forest management adaptation regarding predicted
climate changes and phytophagous insect inuence.
2. Climate inuence on insects
The basic climate parameters, i.e. temperature and
humidity, inuence insects both directly and indirectly.
The direct inuence can be observed through limiting
and stimulating the activity of larvae and adults,
insects dispersal in the environment, phenology and
growing length, as well as through the possibility of
surviving in adverse weather conditions population
genetics, etc. Indirect inuence includes a climate
inuence on environment where insects appear, such
as inuence on plant formations, plant phenology,
food quality, predators, parasitoids and activity of
entomopathogens.
It should be emphasised that the present review
does not exhaust the subject and the list of all possible
relations between climate changes and insects population
dynamics. However, it is essential to present examples
of basic interactions that occur between aforementioned
elements.
2.1. Direct inuence
2.1.1. Activity
Insects as poikilothermic animals change their
activity visibly depending on the temperature of the
surrounding environment (Bale et al. 2002; Menéndez
2007). Increasing the temperature to the thermal optima
level causes acceleration of the insect metabolism.
Hence, it directly inuences their activity increase.
In the temperate climate zone conditions, the average
temperature increase is followed by i.a. more intensive
and longer total day and night’s activity of imago of
majority phytophagous species in forest environment,
implied as feeding and mating, as well as time spent
on nding proper place for laying eggs (Moore, Allard
2008; Netherer, Schopf 2010). It can also result in
insects dispersion increase in the forest environment,
as well as more frequent oviposition and possibility of
colonising larger number of host plants.
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2.1.2. Length of insect growth
In higher temperature conditions, the development of
egg, larva and pupa shortens, which is the characteristic
phenomenon for large group of forest species
(Szujecki 1998). Faster development of preimaginal
stages implies shorter time of exposure to adverse
environment conditions such as low temperature, too
high or insufcient humidity, attacks of predators and
parasitoids, and entomopathogen’s activity. It can result
in reproductive success of many insect species.
Temperature inuence on a length of larval
development has been observed under laboratorial
conditions for two signicant species of native
foliophages: the nun moth, Lymantria monacha (L.)
and the gypsy moth Lymantria dispar (L.) (Karolewski
et al. 2007). In both cases, temperature increase has
had an inuence on reducing growth period, from egg
phase to pupa. Different results have been obtained
regarding larva survivability of both species. When
the average environment temperature has increased,
higher mortality has been observed for caterpillars of
L. monacha. Whereas the survivability of L. dispar
larvae has increased. These differences probably result
from two different thermal optima for both species
reected in varied environmental preferences. The
results of the described experiment present variety of
climate parameters’ inuence on the insect development,
even when closely related species are compared.
2.1.3. Phenology
Under the temperate climate zone conditions,
periodicity of insect activity in the environment is
inuenced by a sequence of seasons. Temperature
is particularly important as a factor that limits insects
activity. Average temperature changes are interrelated
with changes within insect phenology. It is one of the
well-documented sign of a global warming. Earlier
appearance of some species in spring and their longer
activity are the most characteristic symptoms of
a global warming (Walther et al. 2002; Logan et al. 2003;
Parmesan, Yohe 2003; Menéndez 2007; Moore, Allard
2008). The described examples can have a signicant
inuence with regard to herbivores that develop more
than one generation during the year. Average temperature
increase causes faster growth and can have an inuence
on generation number increase of these species. As
a result, biological life cycle is shortened and the larva
number on the one host plant, as well as outbreaks
frequency, increases. Negative inuence of the average
temperature increase on the forest management is
observed with regard to European spruce bark beetle Ips
typographus (L.), which is the most dangerous pests of
this tree species in Europe, including Poland (Jönsson et
al. 2007; Netherer, Schopf 2010).
Winter climate conditions are key importance for
many insects of the temperate climate zone. Temperature
increase in winter can cause survival increase, what
occurs especially in northern and upper range borders,
where extreme low temperature usually causes higher
mortality within the population. However, many species
is not able to nish the developmental cycle or to
continue feeding in spring without sufcient number
of low temperature days (Jönsson et al. 2007; Netherer,
Schopf 2010). Decrease of snow retention as a result
of average temperature and humidity increase can also
have a negative inuence on species that overwinter in
forest bed and soil (Nupponen et al. 2010).
2.1.4. Population genetics
Climate changes can cause faster evolutionary
adaptation than usually. Menéndez (2007), Moore and
Allard (2008) and Régnière (2009) have presented
a short review of researches on it regarding selected
insect species. They have observed how European
buttery Brown Argus Aricia agestis (Den. & Schiff.)
adapted to new thermal conditions in short period
of time by shifting diapause-inducing temperature
threshold. Another example of such phenomenon is the
chrysomelid beetle Chrysomela aeneicollis (Schaeff.)
for which an increase in allele frequency responsible for
the synthesis of low-temperature proteins resistance has
been observed. Hill et al. (1999) have presented results
that show morphological changes in the population of
the buttery Pararge aegeria (L.). Individuals from the
population that colonised new areas in Great Britain for
20 years before the studies have started had larger wing
area surface as well as weight of the thorax in comparison
with individuals from the settled populations. The
increase in dispersal forms has also been observed
on the British Isles for the two bush-cricket species
Conocephalus discolor (F.) and Metrioptera roeselii
(Hagenbach) that have extended their previous range
(Thomas et al. 2001).
There are also examples of forest phytophages that
show high adaptive capability to dynamically changing
environmental conditions. Larvae of the Winter Moth
Operophtera brumata (L.), which is the important
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folivore of deciduous trees and shrubs, hatch in early
spring, after overwintering in egg stadium on host
plants’ shoots. The time of hatching is crucial for the
species. In case of too early hatching in relation to buds
and leafs growth, mortality of caterpillars increases as
a result of starvation. However, the recent research has
showed that there is a natural selection in O. brumata
populations that favours genotypes characterised by
slower egg development (Asch 2007). As a result, hatch
occurs few days later nowadays than it was previously
and because of that a synchronisation of caterpillar
hatching with bud burst is preserved.
2.2. Indirect inuence
2.2.1. Inuence on physiology and metabolism
of host plants
Temperature and humidity change can inuence
insects indirectly by changes in host plants metabolism
and physiology (Ayres, Lombardero 2000; Rouault et
al. 2006; Moore, Allard 2008; Netherer, Schopf 2010).
In general, it is indicated that long and intense
droughts, as one of the average temperature increase
results, have negative impact on plants’ condition, thus
increasing their susceptibility to phytophagous insects.
Dying of oak stands, as a result of water shortage followed
by folivore, cambiophage, and xylophage attacks, is
a current example of such interaction observed in Europe
(Thomas 2008). Although a moderate temperature
increase (as well as and CO2 concentration) can cause
a decrease in food quality for some foliophages, as
a result of nitrogen level decrease in foliage, as well as an
increase in the synthesis of secondary metabolites, e.g.
tannins (Buse et al. 1998; Dury et al. 1998; Kuokkanen
et al. 2001). It has an inuence on deterioration of plant
as food and may increase plant resistance.
Huberthy and Denno (2004) and Rouault et al. (2006)
have conducted a result meta-analysis regarding the
inuence of plant humidity shortage on development,
survivability and fertility of phytophagous insects. Their
studies have been inspired by observed discrepancy
between outbreaks number in natural environment that
often occur after droughts, and results that have showed
negative inuence of water shortage on phytophagous
insects. Analysis results have indicated that reactions of
phytophagous insects to water level decrease in plants
tissues depend on their afnity to ecological guilds, so
to the group of species sharing similar feeding habit.
Positive inuence of drought (especially long-lasting
drought) has been observed with regard to insects
developing in wood, whereas the decrease in water and
turgor level in plant cells has had negative inuence on
species that suck out liquids from tissues (aphids) and
on species that develop in galls. Analysis results of the
inuence on other phytophagous insects, external leaf
feeders and leaf miners, have been ambiguous.
2.2.2. Host plant phenology
Development of many phytophagous insects is
closely related with host plant phenology (Szujecki 1998;
Bale et al. 2002) that is mainly regulated by temperature
conditions in the environment. The same factor, such as
average temperature increase, can inuence differently
on plants and phytophagous insects. Examples of
negative inuence of climate changes are described,
e.g. resulting from disruption of synchronisation of
important processes occurring at different trophic levels
of the ecosystem. For instance, higher temperature in
early spring can cause earlier development of oak leaves
what results in disruption of synchronisation between the
process and the hatching of winter moth larvae (Visser,
Holleman 2001). Similar interrelation has been observed
for the nun moth for which the development of the rst-
instar larvae is usually correlated with the formation
of the owers in Scots pine. Male owers of pine trees
are highly important food for the nun moth larvae, by
increasing species survival and faster development, and
any disturbance of the interrelation affects the species
negatively (Laryšev 1968; Śliżyński 1970; Withers,
Keena 2001). The tortricid moth Zeiraphera griseana
(Hbn.) is another example of the similar interrelation.
However, faster plant growth in spring and longer
vegetation can be benecial to these phytophagous
species that develop inside plant organism. It applies
to some European spruce bark beetle species that can
have extra generation during the year (Netherer, Schopf
2010).
2.2.3. Activity of natural enemies
Natural enemies are another element of the
ecosystem by which climate changes inuence
indirectly phytophagous insects. Enemies activity and
effectiveness and the way of inuencing phytophagous
populations can be diverse. Furthermore, interrelation
of both the elements (phytophages versus natural
enemies) is complicated by indirect climate inuence
on host plants. For instance, lower food quality of
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plants in result of drought causes longer development
of phytophages (see Section 2.2.1) what determines
higher probability of the attacks of natural enemies,
such as predators and parasitoids (Coviella, Trumble
1999; Rouault et al. 2006). On the other hand, plant
chemism change, caused by climate parameters
inuence, results in quality change (size and chemical
contents) of phytophagous insects as hosts, for example,
of parasitoid larvae. It inuences elements as parasitoid
effectiveness of the victim search, the egg number, the
size and sex ratio (Coviella, Trumble 1999).
Higher temperature as the stimulating factor can
cause activity increase of natural enemies and their faster
development (Netherer, Schopf 2010). Temperature
inuence can also regard phytophagous insects itself
and as such it can inuence their susceptibility to
enemy attacks. For instance, under higher temperature
conditions, weaken reaction for alarm pheromones,
produced in case of predator or parasitoid attack, has
been observed for aphids (Awmack et al. 1997). On
the other hand, faster development, induced by higher
temperature, especially in instars exposed to parasitoid
attacks, can result in higher survivability of some
phytophages (Petzoldt, Seaman 2006).
3. Climate changes’ effects observed
in forest ecosystems in result of
entomofauna inuence
3.1. Range shift of phytophagous insects
The current distribution pattern of most insect
species is an effect of climate. The phenomenon can
be observed particularly on range borders where
temperature is a main limiting factor. For instance,
–16°C is the critical value for North American species
of bark beetle Dendroctonus frontalis Zimm., one of the
most dangerous pests for coniferous trees in the region.
Nearly absolute mortality of the population occurs
below this value. Such temperature is observed on the
northern range border of the aforementioned species
(Ayres, Lombardero 2000). It implies that average
temperature increase can enable more termophilous
species to expand in the northern direction and on higher
altitudes. Simultaneously, southern and lower range
borders can be shifted (Parmesan 1996; Walther et al.
2002; Parmesan, Yohe 2003; Menéndez 2007; Battisti
2008). With regard to many phytophagous insects,
a range increase is probable also because species’ ranges
are smaller than areas where their host plants grow.
Many examples of insects’ range shift were
observed in recent years. In the 1990s, few leaf mining
moths of the family Gracillariidae have occurred in
the Central Europe, including Poland (Šefrová 2003).
The horse-chestnut leaf miner Cameraria ohridella
Deschka & Dimić that attacks horse chestnuts Aesculus
hippocastanum was the most spectacular example
among them. Apart from accidental introduction of the
pest, shifting of the northern and eastern range borders,
as a result of temperature increase, was the most
probable cause of the species expansion to new areas.
Range shift of forest folivores in Europe has been
well researched for two species of geometrid moths,
Winter moth, O. brumata, and Autumnal moth, Epirrita
autumnata (Borkh.), in forest stands of northern
Scandinavia (Jepsen et al. 2008). Cyclic outbreaks have
been observed for both species in the aforementioned
area sometimes leading to substantial loss of foliage.
For the last 15–20 years, areas of both defoliators’ mass
outbreaks have increased signicantly. Operophtera
brumata, a species less resistant to low temperature, has
expanded to the north-east to areas where E. autumnata
was the dominant species so far. The latter has increased
range to areas located inland and characterised by
cooler climate. According to authors range increase
for both species results from increase of both average
year temperature and minimum winter temperature. The
Pine processionary moth Thaumetopoea pityocampa
Den. & Schiff is another well-documented example of
the species range shift with regard to the inuence on
forest management. The species is recognised to be one
of the main foliophagous pests in the Mediterranean
region. Temperature in winter, when caterpillars feed
on needles of various pine species (rarely on other
coniferous species), is the main factor that inuences
range limits of T. pityocampa. From the mid-1970s to
2004, the species enlarged its range in France to the
north direction by almost 90 km. In the same period,
its upper range border in Italian Alps moved up by over
200 m in some regions (Battisti 2008; Battisti et al.
2005). Same observations have been made for changes
in an upper range border of the species in Spanish Sierra
Nevada (Hódar, Zamora 2004). Average temperature
increase enabled expansions to areas that have not been
colonised before. Higher survivability of caterpillars
in winter, during feeding time, was observed (Battisti
et al. 2005, Buffo et al. 2007), whereas warmer nights
in summer (with temperature over 14°C) inuenced
distance and altitude increase of female expansion
(Battisti et al. 2006).
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It has been often pointed at the necessity of constant
monitoring of insects range shifts and of selecting
either species or groups of insect species that would
indicate changes in forest environment (for instance,
Ayres, Lombardero 2000; Bale et al. 2002; Logan et
al. 2003; Menéndez 2007). Attempts at predicting
species range shift have also been made (for instance,
Williams, Liebhold 1995 a,b; Jönsson et al. 2007;
Régnière 2009). Apart from ecological requirements
of indicator organisms, varied factors are included
in the aforementioned research, such as typology (for
instance, the type of habitats and plant formations)
and climate parameters (average, minimum and
maximum temperature/precipitation per month). The
variability of the latter implies noticeable bias in any
attempts to predict changes in insects range. Hence,
such predictions can only be seen as possible scenarios.
Results can be inuenced by relatively small changes in
parameters that with regard to climate unpredictability
(even in few-year scale) can hinder from making any
exact prognosis.
Williams and Liebhold (1995a, b) have conducted
prognostic research on insect range shift. They have
used data on defoliated forest stands in the states of
Oregon and Pennsylvania that were previously exposed
to attacks of tortricid moth Choristoneura occidentalis
Free and of L. dispar. Alternative scenarios have
been discussed that included: (a) average temperature
increase by 2°C and unchanged precipitation level, (b)
average temperature increase by 2°C and precipitation
level decrease by 0.5 mm/day and (c) average increase
in values of both parameters. Average temperature
increase and unchanged precipitation level have been
factors that caused L. dispar expansion increase, while
predicted range of Ch. occidentalis has decreased. The
assumed temperature increase and precipitation level
decrease have caused range decrease of both defoliators,
whereas increase of both parameters was positively
correlated with the growth of the outbreaks areas.
Similar research has also been conducted in
Finland (Vanhanen et al. 2007). Probable range shifts
of L. monachal and L. dispar have been predicted
on the basis of selected average temperature change
scenarios that are included in Intergovernmental
Panel on Climate Change (IPCC) report of 2001.
Each simulation (i.e. temperature increase by 1.4, 3.6
and 5.8°C) has initiated range shift for both species.
Northern and southern range borders of both species
have shifted by 500–700 and 100–900 km, respectively,
in the North Pole direction.
3.2. Activity of phytophagous insects
and its harmful effects: outbreaks frequency
Many insect species belongs to the group of pests
with regard to the forest management. Cyclic outbreaks
of some phytophagous insects are connected with forest
condition decrease, losses in forest production and
with bearing high costs of controlling pest population.
Therefore, it is essential to answer the question to what
degree predicated climate change will interrelate with
negative inuence of insect species on forests.
American researchers have conducted interesting
studies in this respect (Currano et al. 2008). They have
analysed plant fossils dated for 59–52 million years
(at the turn of the Paleocene and Eocene). One of the
highest temperature increases was noted on Earth
at this time (by about 6°C) in result of larger CO2
concentration in the air. According to authors the then
climate conditions on Earth can be compared to the
current situation. They have observed that the average
level of damages of leaf lamina made by folivores
and the average temperature increase, as well as CO2
concentration, were positively correlated. It was
explained by the increase in CO2 concentration in the air
which interrelates with increase in carbon-to-nitrogen
ratio in plant tissues resulting in decrease in the nutritive
values of the foliage. Hence, losses from lower leaves
nutritional value need to be compensated by higher
consumption. Comparing the aforementioned results
with the currently observed climate changes, increase
in defoliation levels should be expected, followed by
increased damage of forest stands (Rouault et al. 2006;
Battisti 2008; Currano et al. 2008; DeLucia et al. 2008).
Changing thermal conditions and humidity both can
have positive and negative inuence on insects. Battisti
(2008) has given an example of two forest phytophages
on which temperature increase had signicantly different
inuence. Between 1985 and 1992, an unexpected mass
outbreak of web-spinning sawy Cephalcia arvensis
Panzer, an oligophagous hymenopteran species
associated with spruce, was observed in Southern Alps.
The species usually do not have a tendency to a mass
outbreaks, which result from limited dispersal abilities
and low female fertility, as well as from long (even up
to few years) diapause followed by higher mortality in
the population. According to authors, the outbreak of
C. arvensis was caused by few-year-period of high
average temperatures and drought in June and
July, during larval feeding time. On the one hand,
higher temperature and low humidity caused shorter
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development of larvae of C. arvensis; on the other
hand, enabled faster pupation and avoiding the longer
diapause. In effect, the species has produced generation
once a year for few years, which caused sudden eruption
of population density.
The opposite phenomenon has also been observed
in the region of Alps for another folivore species, Larch
Tortrix Zeiraphera griseana (=diniana). The species
develops on few coniferous species; however, its main
host plant in the discussed area is larch. The species is
of great signicance because of 8- to 10-year cycles
of outbreaks; the history of which was estimated on
the basis of dendrochronological research dating back
over a thousand years (Esper et al. 2006). Caterpillars
of Z. griseana hatch in spring and commence feeding
on developing needles. Starting from 1989, a signicant
decrease in the number of larch tortrix has been
observed for few seasons. In effect, the number of
outbreaks has dropped as well. Meteorological analyses
have showed that high temperature in winter and spring
inuenced higher mortality of eggs and disturbance
of synchronisation between eggs ’hatch and needles’
development.
Climate change can also cause higher activity
of pest species that was not signicant before for the
forest management in the area. The outbreak frequency
of the European pine sawy, Neodiprion sertifer
(Geoff.), regarding temperature increase and selected
environmental elements, has been analysed in Finland
(Virtanen et al. 1996). Research has showed that days
with the temperature lower than –36°C in winter is the
main factor limiting N. sertifer outbreaks in the Northern
Finland because the high mortality of eggs is observed
below this temperature. The same research has focused
on scenario of the average winter temperature increase
by 3.6°C to 2050. According to authors, the global
warming can cause increase in the outbreaks frequency
of the European pine sawy in areas where the species
does not occur or occurs sporadically.
Similar simulations regarding population dynamics
of European spruce bark beetle have been performed
in Southern Sweden (Jönsson et al. 2007). Currently,
the species has only one generation during the year in
the researched area. By predicted increase in yearly
average temperature by 2–3°C, the second swarming of
the beetles is possible and increase by 5–6°C can cause
development of the another generation. However, the
authors have noticed that favourable thermal conditions
for I. typographus can occur nor every year, even if
the predicted scenario will be realised. Adequately
early time of spring swarming and shorter period of
development preimaginal stages inuence the possible
development of the second generation of the species.
3.3. Invasive species
Insects belong to the group of animals where alien
species are the most frequently represented for the area.
Climate change can result in adaptation, population
increase and expansion of alien species that are better
adapted than native taxa (Capdevila-Argüelles, Zilletti
2008). Temperature increase can positively inuence
the population number of introduced species whose
development and survivability were limited before by
low temperature. Apart from climate change, human
activity is the signicant factor in the process, such as
intentional or accidental introducing of exotic plants
and phytophagous species.
In European forest ecosystem, two moths in the family
Gracillariidae are claimed to be invasive: Parectopa
robiniella Clem. and Phyllonorycter robiniella (Clem.)
that arrived to Europe from North America (Šefrová
2003). Caterpillars of both species develop in leaf mines
on the leaves of the black locust Robinia pseudoacacia
L., a tree species introduced in Europe at the beginning
of the 17th century. Even though the host plant has been
present for the several centuries in Europe, both insect
species were recorded for the rst time in the second
half of the 20th century in the Southern regions of the
continent. Since then, the expansion process is observed
in the Northern direction, and the phenomenon is usually
explained to be caused by global warming.
3.4. Host shifts of phytophagous insects
Insect range shifts, resulting from changing climate
parameters inuence, can also cause insects adaptation
to new host plants. The situation occurs especially when
closely related species of the host plant exists in the
new range of the phytophagous insect. Widening of host
plants spectrum or even a change in feeding preferences
by using available niches can occur. Thaumetopoea
pityocampa, observed in Serra Nevada Mountains, in
southeast Spain, is an example of such a phenomenon.
The average temperature increase for the last several
decades enabled species dispersion to the higher
altitudes where it has not existed before. Range shift
was accompanied by adaptation to the new host plant,
i.e. a relict subspecies of Scots pine, Pinus sylvestris var.
nevadensis (Hódar, Zamora 2004).
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T. Jaworski et J. Hilszczański / Forest Research Papers, 2013, Vol. 74 (4): 345–355.
352
4. Forest management adaptation
to climate change with regard to
entomofauna inuence
The contemporary forestry faces many challenges
and predicted climate change is one of the most
important among them. Climate parameters change
will have both positive and negative inuence on forest
ecosystems. In the temperate zone, longer vegetation
and faster photosynthesis are expected in result of
higher CO2 concentration. It can result in higher wood
production. Stress factors, such as water shortage,
adverse weather phenomenon and higher pathogen
and phytophages activity, can cause deterioration of
the forest condition. Therefore, changes in structure,
productivity and functioning of the forest ecosystem can
also be observed in result of predicted climate change,
and it can inuence forest management. Because of
the aforementioned issues, it is crucial to adapt forest
ecosystems and forest management to climate changes
(Rezolucja H4 1993; Spittlehouse, Steward 2003;
Moore, Allard 2008; Netherer, Schopf 2010).
Forestry adaptation to climate change can be
discussed as:
- a spontaneous process, although limited and
proceeding at too slow pace in comparison to change
progression and
- a process of forest and forestry adaptation
that should be proceeded by a sensible way of forest
management; it should include current and predicted
climate changes and secure complete productive,
ecological and social role of the forest or at least, should
minimise wastes within these roles.
The former denition of adaptation results from
natural ability of forest ecosystem to adapt to new
conditions; the latter also includes modication in
current law and regulations.
The strategy of adaptation of forests (natural
ecosystems) and forestry (practices and forest
management) to climate change with regard to inuence
of insects should be considered in all its bearings. Part of
the strategy will not differ from general directions that
have been used in forestry for many years. Regarding
stability and stress resistance of the forest stand,
including insect attacks, adjusting species composition
of the stand to habitat’s conditions is important. It
is hoped to use natural tree (species, populations,
phenotypes) resistance against insect attack; however,
these actions should be preceded by a research on
resistance heredity. Including phenology of trees and
their pests in forest plans can prevent or limit defoliation,
for example, in result of disturbing synchronisation
between bud burst and leaf development and hatching
of larvae. Introducing late-developing oak species
forms could be a good example of such actions because
it is more resisted against damages caused by frost and
foliophages in the spring. Species of lower susceptibility
to water shortage should be prioritised because it can
limit the primary weakening of tree conditions and
forest stands what is important in case of drought,
and in results, can reduce the risk of the secondary
attacks of phytophagous insects. The sessile oak Quercus
petraea or the grey alder Alnus incana are examples
of the tree type that have lower water requirements in
relation to the common oak Quercus robur and black
alder Alnus glutinosa, which are currently more popular.
Water retention in forests should be introduced and
maintained to limit the risk of stress related to water
shortage and, indirectly, to secondary pests attacks.
Global warming is conducive to range shift of some
organisms, including many pest species. The risk for
invasive species occurrence and damage resulting from
their inuence on forest ecosystems can be sometimes
estimated in advance on a basis of knowledge about
ecological requirements of phytophages and host
plants distribution. New, modern tools, geographic
information system, simulation and prognostic models
among others, can enable to achieve it (Williams,
Liebhold 1995a, b; Jönsson et al. 2007; Vanhanen et al.
2007; Régnière 2009). It will be essential to include in
a future management planning elements of variability
and uncertainty, as well as risk analysis and decision
support system in case of new pest species occurrence
(Moore, Allard 2008; Chmura et al. 2010; Netherer,
Schopf 2010). Together with the trade development,
the amount of transported goods and new areas of their
distribution, it is the increased risk of alien species that
will be signicant for the forestry. Therefore, wood trade
control and quarantine regulations will have a signicant
role. It is also necessary to develop effective system of
detecting, monitoring and controlling invasive species.
5. Conclusions
There are currently many evidences for climate
change on Earth. The most popular hypothesis states
that average temperature will increase in result of higher
CO2 concentration in the atmosphere, among others.
Predicted changes will have a signicant inuence
on forest ecosystems and on all elements of forest
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T. Jaworski et J. Hilszczański / Forest Research Papers, 2013, Vol. 74 (4): 345–355. 353
biocenosis: both trees that are forest’s basic component
and other groups of organisms. Climate changes are
important for phytophagous insect species, and basic
climate parameters – temperature and humidity –
inuence it both directly and indirectly. Research,
performed to estimate climate change inuence on insect
development and activity, often produced equivocal
results. However, on the basis of the result synthesis,
the following general conclusions can be made:
1. Global warming is conducive to polyphagous
and eurytopic species. It results from higher ecological
plasticity and adapting abilities of the organisms.
2. The general observations of the climate change
inuence on phytophagous insects suggest that the role
of thermophilous species has currently increased. This
results mainly from range shift to the northern direction
and to higher altitudes.
3. In result of changing climate conditions, some
phytophagous species status can change, the role some
species can increase, while the other can decrease.
4. The number and the role of phytophagous species
overwintering in egg stage have increased in comparison
to species that overwinter in other development stages.
It relates to average temperature increase in winter as
larvae, pupae and the adults show higher mortality at
that time, whereas eggs have probably higher resistance
to low temperatures.
5. Stress, which results from water shortage, is one
of the global warming consequences. It can have varied
inuence on phytophagous insects population dynamic.
An effect of the inuence is related not only to frequency
and the level of water shortage but also to the trophic guild
that a phytophagous species belongs. In general, species
developing in wood present positive reactions to moderate
decrease of humidity. Humidity shortage negatively
inuences species that suck sap from plants tissues as well
as gall-makers. Research regarding typical foliophages as
well as leaf-miners does not give unequivocal results.
6. Climate change together with constantly increasing
trade can be conducive to invasive phytophagous
insect species. Absence of effective natural enemies in
new areas and higher plasticity of invasive species
in comparison to native species can cause higher level
of damage in forest ecosystem.
Acknowledgements
This research received no specic grant from any
funding agency in the public, commercial or not-for-
prot sectors.
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