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Criminal
cases can often only be solved using forensics to piece together
physical evidence and reconstruct what happened. Prof. Dr. Helmut
Schmitz from the Institute of Zoology at the University of Bonn and Dr.
Herbert Bousack from the Peter Grünberg Institut at the Forschungzentrum
Jülich went through the same experience. Prof. Schmitz has been
researching fire beetles of the genus Melanophila
and their sophisticated IR sensors, which these pyrophilous insects use
to detect forest fires, for many years. This is a very special
ecological niche.
“It
allows the beetle larvae to freely eat their way through the wood
because the trees, which have been killed by great heat, can no longer
fight back, and there are hardly any predators that would eat them in
freshly burned forests,” the Bonn zoologist reported.
A tiny sphere senses changes in pressure due to heat
Meanwhile,
with the help of the Forschungszentrum caesar in Bonn and the
Technische Universität Dresden, the researchers have unraveled the
functional principle of this so-called photo-mechanical beetle infrared
sensor, and they have started to work on a technical reconstruction of
this natural prototype. Tiny cuticula spheres of the beetles’ IR
receptors—at 0.02 mm, smaller than the diameter of a fine hair—are
filled with water and absorb IR radiation very well. Due to the fact
that they heat up, the water in particular expands suddenly, and the
resulting change in pressure is immediately detected by highly sensitive
mechano-sensitive sensory cells.
“However,
an important question had remained unanswered—how sensitive is the
sensor?” asked Schmitz. This question could be best answered by
equipping Melanophila beetles with mini transmitters on their search for forest fires.
“Then
we would be able to log the distance flown to the burnt area and, based
on this distance, calculate the minimum required heat radiation the
beetles are attracted by,” explained the zoologist. But at a length of
about 1 cm, the beetles are too small to carry a transmitter for long
distances.
In 1925, a blaze destroyed a large oil storage facility in California
The
resourceful scientists turned to a past event, which proved helpful. In
August 1925, a large oil depot in Coalinga, California, went up in
flames.
“Reports from that era mentioned that the huge blaze attracted masses of charcoal beetles (Melanophila consputa),”
explained Schmitz. Since the fire location was in the forest-less
Central Valley of California, the beetles must have flown in from a
great distance. Most likely, they came from large forests on the western
foothills of the Sierra Nevada about 130 km away, where there had been
large forest fires in the two preceding years.
“On
such burnt areas, beetles multiply en masse, and after they emerged,
they went to look for forest fires in the subsequent summers,” said
Schmitz.
A
forested area about 28 km from the burning oil tanks in the San Benito
Mountain Natural Area north of Coalinga seems rather unlikely as the
source of the beetles since forest fires had not been reported in this
area prior to 1925.
Based on a model from fire protection technology
Scanning electron micrograph of the spherical infrared receptors of the black pine borer (Melanophila acuminata). Photo: Don Larson / University of Bonn |
Dr.
Herbert Bousack, an engineer from the Peter Grünberg Institut at the
Forschungszentrum Jülich performed the calculations for modeling the
sensitivity of the sensor.
“The
Coalinga fire is a good match for this simulation,” Bousack reported.
First however, many parameters had to be researched painstakingly, such
as the size of the fire, or the weather conditions. “More than 85 years
after the event, such data was hard to obtain.”
The
engineer based his mathematical simulation on various fire models such
as are used in assessing of fire risks for storage tank facilities. “We
adapted these technical guidelines for our purposes, which allowed us to
fall back on proven experiences,” said the engineer.
According to the math, the beetle sensor is incredibly sensitive
The result was amazing. “According to our calculations, the infrared sensors of Melanophila
beetles should be able to sense signals even if they are below the
level of thermal noise,” reported Bousack. Obviously, the beetles rely
on stochastic resonance.
“This
method enables them to detect weak periodic signals that are normally
superimposed by the noise,” explained the engineer. According to the
results of the calculations, the sensors can detect the tiniest amounts
of heat—roughly comparable to the energy resolution of radio telescopes.
“Our simulations and calculations make it seem quite probable that the IF sensors of pyrophilous Melanophila
beetles are more sensitive than uncooled infrared sensors currently
available in the market,” Prof. Schmitz summarized the outcome.
“Additional efforts to implement this natural prototype technologically
will be required.” So, they might be able to revolutionize early-warning
systems for forest fires.
Source: University of Bonn
