WIND-EVOKED EVASIVE RESPONSES IN FLYING COCKROACHES

1) A standing cockroach (Periplaneta americana) responds to the air di splacement made by an approaching predator, by turning away and runnin g. The wind receptors on the cerci, two posterior sensory appendages, excite a group of ventral giant interneurons that mediate this respons e. While flying, these interneurons remain silent, owing to strong inh ibition; however, the dorsal giant interneurons respond strongly to wi nd. Using behavioral and electromyographic analysis, we sought to dete rmine whether flying cockroaches also turn away from air displacement like that produced by an approaching flying predator; and if so, wheth er the cerci and dorsal giant interneurons mediate this response. 2) W hen presented with a wind puff from the side, a flying cockroach carri es out a variety of maneuvers that would cause a rapid turn away and p erhaps a dive. These are not evoked if the cerci are ablated (Figs. 4, 5, 6). 3) This evasive response appears to be mediated by a circuit s eparate from that mediating escape when the cockroach is standing (Fig . 7). 4) The dorsal giant interneurons respond during flight in a dire ctional manner that is suited to mediate this behavior (Fig. 8). 5) Re cordings of the wind produced by a moving model predator (Fig. 9), tog ether with measurements of the behavioral latency of tethered cockroac hes, suggest that the evasive response would begin just milliseconds b efore a predator actually arrives. However, as explained in the Discus sion section, under natural conditions, the evasive response may well begin earlier, and could indeed be useful in escaping from predators. 6) If cockroaches had a wind-mediated yaw-correcting behavior, as locu sts have, this could conflict with the wind-evoked escape. In fact, co ckroaches show the opposite, yaw-enhancing response, mediated by the c erci, that does not present a conflict with escape (Figs. 10-14).