A Beetle Sensor Recognises Fires

Photo: IR-organ of the beetle

It is inconspicuous: small, black and hard. But it is able to do something that in its kind is not known in nature thanks to a structure that sticks to its head – two small antennae with which the beetle can sense infrared emission of a burning forest more than 50 kilometres away. The Melanophila acuminate beetles need to be able to do so because females need charred tree bark in order to lay their eggs.

It has been known for nearly 50 years that this insect has fire sensing organs. The zoologist Dr. Helmut Schmitz from the University of Bonn has been looking for many years at the mechanics behind this. And he discovered something surprising: „The beetle can sense the infrared emission with a mechanical sensor not a thermal one“. This means: The beetle’s sensor organ does not measure the temperature itself - it measures the deformation of a sensor membrane.

The organs inside the antennae are all built up following the same principle. Many tiny cavities filled with a fluid are located inside a sphere and are connected to each other. A mechanoreceptor that is sensitive to pressure sticks with its end into one of these cavities. If infrared emission warms up the liquid and the sphere both of them expand. This results into increasing pressure which is transferred to the receptor.

 
 

Photo: Structure of the IR-sensor

After Schmitz deciphered structure and function of the antennae’s inner he built a model of it. “This model is based upon a microfluidic approach “, says Schmitz. “ Three years ago he approached Dr. Michael Tewes and Dr. Markus Löhndorf at the Research Centre caesar in Germany and they validated the feasibility to construct a sensor based upon this model in the micrometer scale.

The result now is a silicon wafer with 100 micrometer in diameter and small holes that are supposed to simulate the cavities. Two electrodes are attached near the holes. „If the ionic liquid that we use expands due to increased infrared emission the electrodes are connected with each other through the liquid. This equals the signal that is measured by the real mechanoreceptors in the beetle”, says Tewes. This new technology could be useful in infrared cameras for houses, as a sensor for night vision gear in cars or a warning system for fires.

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