Ronald R. Hoy
Sect. of Neurobiol. & Behavior, Mudd Hall, Cornell Univ., Ithaca, NY 14853
Insectivorous bats detect and hunt down their prey by means of ultrasonic biosonar signals and some insects have evolved ultrasound-sensitive ears to detect bats and to take evasive action. This has been known since the early 1960s, largely due to the pioneering work of K. D. Roeder, who documented the interactions between bats and moths, that hear ultrasound. Since then, studies of the auditory behavior of insects has revealed that ultrasound hearing has evolved in at least five orders of nocturnally active, flying insects and it is suspected that it serves to detect the biosonar signals of bats. In spite of the taxonomic diversity (unrelatedness) of these insects, all insects that hear ultrasound have evolved a tympanal hearing organ with particular and characteristic ``design features'' in their structure and function. When some of these insects are stimulated with ultrasound during tethered flight, they exhibit short latency startle responses that appear to be escape behavior, ranging from directional steering to cessation of wingbeat. It is clear that the predatory relationship between bats and their insect prey has resulted in the evolution of evasive behavior in insects, made possible by the evolution of a hearing organ sensitive to ultrasound.