Navigation to forest fires by smoke and infrared reception: The specialized sensory systems of "fire-loving" beetles

"Fire-loving" (pyrophilous) beetles depend on forest fires for their reproduction. Such insects approach ongoing fires and invade the burnt area immediately. Two genera of pyrophilous jewel beetles (Buprestidae) and one species of the genus Acanthocnemus (Acanthocnemidae) show a highly pyrophilous behaviour. For the long-range navigation towards a fire as well as for the short-range orientation on a freshly burnt area these beetles have special sensors for smoke and infrared (IR) radiation. Whereas the olfactory receptors for smoke are located on the antennae, the IR receptors are housed in extraantennal sensory organs which can be found on the thorax or on the abdomen. In the best-studied beetle, Melanophila acuminata, infrared receptors and their associated sensory neurons are derived from mechanoreceptors. Unlike other mechanosensory neurons, IR sensitive neurons directly send their information to be processed centrally (e.g. by the brain) rather than locally in their respective ganglia of origin. It is suggested that smoke - derived odours and IR information converge on descending brain neurons which, in turn, control and direct flight toward the forest fire.