Infrared Sensory Systems in Pyrophilous Insects

摘要

The highly pyrophilous 'Little Ash Beetle' Acanthocnemus nigricans is attracted by forest fires and is equipped with one pair of unique prothoracic sensory organs. Our results have revealed that these organs most probably serve as infrared receptors. Bach organ consists of a cuticular disc (diameter 150 micrometers) which is fixed over an air-filled cavity. On the outer surface of the disc, about 90 tiny cuticular sensory organs (sensilla) are situated. The poreless outer peg of each sensillum is 2 - 4 micrometers long and is surrounded by a cuticular wall. One ciliary sensory cell innervates the peg, the dendrite of which is divided into an outer and an inner dendritic segment. As a unique feature, the outer dendritic segment is almost totally replaced by an electron-dense rod, which most probably represents the hypertrophied dendritic sheath. The inner dendritic segment and the soma are fused indistinguishably forming a common cellular space. Thin, leaflike extensions of glial cells deeply extend into that enlarged lumen which also contains large numbers of mitochondria. The sensilla of the sensory disc- of A. nigricans obviously represent a new type of insect sensillum. Electrophysiological investigations indicate that the sensilla function as warm receptors. Therefore, the prothoracic sensory organs of Acanthocnemus can be regarded as a micobolometer of reduced thermal mass. If the massive rod inside- a disc-sensillum should function as a heat conducting structure, the Acanthocnemus IR organ can serve as a model for new uncooled IR sensor arrays having a size about one order of magnitude below the size of current microbolometer arrays.