HINDLEG TARGETING DURING SCRATCHING IN THE LOCUST

Intact locusts (Schistocerca gregaria) respond to tactile stimulation of their folded wings with rhythmic scratching movements of the ipsila teral hindleg that are directed towards the site of stimulation. For e xample, sites near the base of a wing elicit anteriorly directed scrat ches, whereas sites near the distal end of a wing elicit posteriorly d irected scratches. Locusts also scratch in response to tactile stimula tion of a wing that is held outstretched in a posture similar to that normally adopted during flight, but they fail to alter their leg targe ting to compensate for this changed position of the stimulus site. Ins tead, they scratch at an empty point in space near the abdomen, where the stimulus site would have been if the wing was folded in the restin g posture. This inappropriate scratching does not result from mechanic al constraints on the hindleg's movement, from stimulation of abdomina l sensory receptors, or from an absence of sensory information from th e outstretched wing. It also persists when the metathoracic ganglion t hat controls movements of the hindlegs is isolated from the remainder of the central nervous system (CNS). Targeted scratching of sites on t he wings of locusts therefore appears to be fixed relative to body coo rdinates and does not take into account alterations of the target wing 's position.