Reproductive Role of Infrared Radiation Sensors of Melanophila
acuminata (Coleoptera: Buprestidae) at Forest Fires
W. G. EVANS
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1
Ann. Entomol. Soc. Am. 103(6): 823Ð826 (2010); DOI: 10.1603/AN10076
ABSTRACT Based on the original experimental results from stimulating the infrared radiation
sensors of Melanophila acuminata (DeGeer) (Coleoptera: Buprestidae), it has been concluded that
the sensors function at forest Þres by protecting beetles from hazardous conditions associated with
a ßaming environment while swarming, mating, and ovipositing on heated, exposed tree roots. The
beetles are renowned for their rapid ßight and for their exceptional dispersal capacity resulting in such
a wide distribution that they come upon Þres randomly. Thus, a case is made here that the infrared
radiation sensors of M. acuminata and, presumably, other species in the genus, evolved not for distance
perception of Þres but for enhanced reproductive activities at them. An examination of the literature
has revealed a long-standing interest in distances of perception of forest Þres by the sensors, during
which time increasingly longer distances have been claimed in various publications. These distances,
however, cannot be accepted because there are no calculations supporting them, but just as important
is that all of them, ranging up to 100 km in length, far exceed distances obtained by application of the
inverse square law of physics where the intensity of radiation of a Þre is inversely proportional to
KEY WORDS Melanophila acuminata, infrared radiation sensors, forest Þres, reproduction
Adults of Melanophila acuminata (DeGeer) (Co-
leoptera: Buprestidae) are renowned for their disper-
sive powers (Wikars 1997) and their ubiquity at forest
Þres (Evans 1971). They are possibly better known,
however, for their infrared radiation (IR) sensors lo-
cated in an elliptical sensory pit adjacent to each
mesocoxa. These beetles are widely distributed over
the Northern Hemisphere wherever forest Þres occur,
even as far north as Fort Fitzgerald, AB, Canada, at
almost 60⬚ N (Specimens in the Entomology Collec-
tion, University of Alberta, Edmonton, AB, Canada).
Yet, their preferred surface temperatures are high,
ranging from 33.5 to 49.5⬚C, with a mean of 40.5⬚C
(Evans 1971), which is comparable with the mean
preferred surface temperature of ⬇40⬚C for second-
stage larvae of the desert locust Schistocerca gregaria
(Forskal) (Chapman 1998) at ⬇23⬚ N in the Sahara
My objectives here are to discuss the published
distances of perception of forest Þres by the IR sensors
and to propose a reproductive role for the sensors at
The ability of M. acuminata to detect IR from forest
Þres has attracted much attention, both in the scien-
tiÞc literature and the popular media. Unfortunately,
there has been a trend over the years for increasing,
but unsubstantiated, reported distances of IR detec-
tion by the beetles. Some examples of published dis-
tances of IR perception (not accompanied by scien-
tiÞc calculations or experimental evidence) are given
50 km. Gronenberg and Schmitz (1999), Ackerman
(2000), Anonymous (2003), Stone et al. (2004),
80 km. Biever (2004), Grimm (2004), Reese (2004),
Lee and Szema (2005), Mueller (2008).
100Ð150 km. Ishay et al. (2004).
50Ð100 miles. McConney (2009).
60Ð100 miles. Campbell et al. (2002).
These references represent sources citing, if at all,
other sources that include biological, engineering,
nanotech, neuroscience, military, and air force jour-
nals; a thesis; a popular magazine; and a nonpeer-
reviewed biological journal. At Þrst glance, they sug-
gest a widespread and ingrained acceptance of an
interesting aspect of insect behavior. Thus, the notion
that M. acuminata can detect IR from Þres consider-
able distances away is widely accepted in the literature
at this time. However, the lack of substantiation for
these distances represents a deplorable scientiÞc pre-
dicament that needs to be acknowledged. It seems that
Corresponding author, e-mail: firstname.lastname@example.org.
0013-8746/10/0823Ð0826$04.00/0 䉷 2010 Entomological Society of America
the only published distances over which IR might be
perceived by the beetleÕs sensors that involved calcu-
lations were 12 km (Schmitz and Bleckmann 1998)
and 1 km Hammer et al. (2001). The former distance
cannot accepted because of important assumptions in
calculations that were omitted (Hammer et al. 2001),
and the latter distance is unacceptable because in their
study the whole spherical chitinous structure of a sensor
was intentionally heated to induce a response when
stimulated by laser produced IR, in contrast to suggested
phasic responses produced by IR heating of the small
volume of air inside the sensor (Evans 2005). Thus, with
no acceptable published distances of perception of IR by
the sensors, calculations are now proposed to determine
IR intensities at distances from a Þre.
Radiation emitted by a Þre ⫽ Exitance (M), is cal-
culated from the following equation (Vincent 1990,
⫻ Þre area (W/m
where is the emissivity factor of a Þre of ⬇0.95 and
is the StefanÐBoltzmann constant of 5.67 ⫻ 10
, where K is temperature of a Þre in Kelvin.
Although peak temperatures of forest Þres are usually
provided in the literature, it is the average tempera-
ture of transient radiant ßux in time and place that is
pertinent here, such as the 1,000 K recorded at an
experimental Þre by Packham and Pompe (1971) or
the average of 900 K in a study of bushÞre radiant
ßuxes and temperatures, even though peak tempera-
tures of 1,200 K were encountered (Debnam 2005).
These average temperatures are close to the 926 K that
correspond to the peak wavelength of IR spectral
sensitivity of 3.13
m (WienÕs displacement law) of
the beetleÕs sensors (Evans 1966).
Therefore, M in W/m
of a 400 m
area Þre is
⫻ 0.95 by 400 m
⫽ 199.5 W/m
The intensity of IR at a distance is inversely pro-
portional to the square of the distance (inverse square
law). Thus, dividing 199.5 W/m
by the square of a
distance from a Þre gives the IR intensity at that
distance. For example, at 1,000 m from a Þre, 199.5
⫽ 0.0002 W/m
. This is an intensity
that is certainly not detectable by the IR sensors that
respond to 0.6 W/m
(see below); similarly, for 50 m,
where the intensity is 0.08 W/m
. But at that distance,
other stimuli such as visual, olfactory (Schutz et al.
1999), and thermal (Evans 1971), probably invoke
responses that guide the beetles to a Þre. Thus, these
results support a conclusion that no published dis-
tances of IR perception by the sensors are valid and
that the IR sensors of M. acuminata and other species
of Melanophila that have the sensors, function at or
Proposed Role of the Sensors in Reproduction
Sensor sensitivity of IR perception by M. acuminata
beetles was originally determined by stimulating the
sensors of one of the mesothoracic sensory pits, with
an IR source of 0.6 W/m
from ⬇2 cm away (Evans
1966). The response was a distinct twitching of the
antenna on the same side of the insect as the sensory
pit being stimulated. Such a short distance for a pos-
itive response suggests that the beetles were respond-
ing as though at a Þre emitting this radiation, and there
are several reasons that support this view. Orienting to
a point source, such as a distant Þre, is not a role for
paired lateral groups of sensors with Þelds of view that
do not overlap anteriorly (Evans and Kuster 1980).
Instead, they would be much more practical for per-
ceiving IR from a wall of ßames as the beetles ßy
parallel to them. In addition, perception of a distant
point source of radiation would not be enhanced by
the beetleÕs phasic IR sensors (Evans 2005) that are
capable of detecting ⬇8-ms changes in motions of
ßames during ßight. Finally, as calculated above, dis-
tance perception of IR from Þres is restricted to ⬍50
m, suggesting that the IR sensors function at or very
close to Þres, agreeing with the suggestion that repro-
duction takes place there (Linsley 1943, Bily´ 1982).
A major characteristic of the beetles is their swarm-
ing behavior toward a Þre at meter heights above the
ground, as noted by Linsley (1933), ÞreÞghters (Eaton
and Kaufman 2007), or, for Melanophila consputa
(Lec), other individuals (Van Dyke 1926). Beetles
also were observed at ground level at a smelter plant
(Linsley 1943), at an oil sludge Þre (Evans 1971), and
a small scrub Þre in Alberta, Canada (unpublished
data). This behavior indicates a predilection for ßying
close to the ground, where mating and oviposition take
place, thus avoiding burning branches higher up.
Swarming has been previously linked to reproduction
along with the suggestion that swarming, mating, and
oviposition are elicited by Þres (Bily´ 1982, cited in
If distance perception of Þres is not an IR sensor
option, then the beetles reach Þres by other means.
Insects dependent on ephemeral habitats, such as for-
est Þres, must have a large dispersal and reproductive
capacity (Southwood 1977). Wikars (1997) enlarged
on this theme by stating that M. acuminata beetles
have an exceptional dispersal capacity as exempliÞed
by their appearance on sea shores very far from forest
Þres. It is very likely that the beetles reach Þres by
chance through these highly dispersive activities. This
behavior also results in beetles reaching campÞres,
and trees freshly killed by wind storms or by logging
(Burke 1919; Evans 1962, 1971). Within short dis-
tances of Þres, dispersing beetles may reach them by
detecting smoke with their antennal olfactory sensors
(Schutz et al. 1999), or temperature sensors (Evans
1971), or perhaps visually as well, resulting eventually
in swarms of beetles ßying close to a Þre where heat
and smoke stimulate ßight, mating, and oviposition.
Reproduction at Þres is greatly increased, because
there are no predators or competitive species of wood-
boring insects, and development is rapid as reduced
length of development ensues when eggs are depos-
ited in bark heated by IR. Palm (1949) recorded a case
where, at the time of a Þre, development of the bee-
tles, which normally takes a year, took 2 mo from
oviposition to pupation. Assuming more or less con-
stant arrivals at a Þre (Van Dyke 1926), beetles at the
NNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 103, no. 6
downwind moving Þre front are continually being
replaced by fresh beetles, resulting in increased re-
production, a speciÞc requirement for insects of
ephemeral habitats (Southwood 1977).
The function of the IR sensors is very evident at a
forest Þre where conditions are unpredictable be-
cause many complex factors are involved, such as
rapid changes in wind speed or direction, topography,
kinds of fuels, atmospheric moisture content, and
weather. Flame ßare-ups can be common, as can
pieces of burning material (Þrebrands) that are car-
ried into the air, to land wherever. It is very likely that
ßying beetles avoid these hazards by detecting sudden
changes in radiant ßux. Thus, it can be concluded that
the sensors evolved to enhance reproductive success
directly at Þres.
I extend my most sincere thanks to George E. Ball (De-
partment of Biological Sciences, University of Alberta) for
critical review of the biological aspects of the manuscript.
And I am most grateful to E. O. Wilson (Department of
Organismic and Evolutionary Biology, Harvard University,
Boston, MA) and to Peter Lawrence (Department of Zool-
ogy, University of Cambridge, Cambridge, United Kingdom)
for advice on dealing with the difÞcult problem of the many
unconÞrmed claims of distance perception of Þres by M.
acuminata. I also thank Chris Evans (Royal Alexandra Hos-
pital, Edmonton, AB, Canada) and Claire Jones (Ichor Med-
ical Systems, San Diego, CA) for critically reviewing the
manuscript. Finally, thanks to Frank Weichman (Depart-
ment of Physics, University of Alberta) for ongoing interest
in the research. The support and encouragement of the
Department of Biological Sciences (University of Alberta) is
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Received 10 May 2010; accepted 15 July 2010.
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