The dorsal giant interneurons mediate evasive behavior in flying cockroaches.

Abstract

ABSTRACT Cockroaches escape from terrestrial predators by making an evasive turn and running away (Camhi, 1984). The air displacement produced by the predator’s strike is sensed by wind-sensitive receptors on the cerci, two posterior antenna-like organs. These receptors excite two distinct populations of giant interneurons, the ventral giant interneurons (vGIs) and the dorsal giant interneurons (dGIs), in the last abdominal ganglion of the nerve cord (Camhi, 1984). The vGIs are known to control the direction of the escape turn when the animal is on the ground (Camhi, 1988; Ritzmann, 1993; Comer and Dowd, 1993; Liebenthal et al. 1994), while the dGIs are known to initiate and maintain flight (Ritzmann et al. 1982; Libersat et al. 1989; Libersat, 1992). Since cockroaches are not equipped with an ultrasonic hearing sense (Yager and Scaffidi, 1993) and consequently do not respond to ultrasound with escape maneuvers, as many other insects do (Hoy et al. 1989; Libersat and Hoy, 1991), it is reasonable to envisage that, while flying, cockroaches may recruit their wind escape circuit to evade aerial predators such as bats. Indeed, recently Ganihar et al. (1994) have shown that flying cockroaches produce various flight maneuvers that should cause an evasive turn away from a wind stimulus. Such flight maneuvers are not produced after cercal ablation. The most likely candidates to mediate these evasive flying maneuvers are the dGIs, because the wind sensitivity of the vGIs is greatly reduced during flight (Libersat et al. 1989; Libersat, 1992). In contrast, the dGIs retain their wind sensitivity during flight (Libersat, 1992) and also they respond in a directionally sensitive manner to a wind puff delivered from the side (Ganihar et al. 1994). In this study, the possibility that the dGIs mediate evasive flying maneuvers was investigated by stimulating individual identified dGIs during flight and measuring the asymmetrical responses in a pair of left and right flight depressor muscles, the subalars of the metathoracic wings.