PHYSIOLOGICAL-PROPERTIES OF WIND-SENSITIVE AND TACTILE TRICHOID SENSILLA ON THE OVIPOSITOR AND THEIR ROLE DURING OVIPOSITION IN THE LOCUST

The physiological properties of the ovipositor hair sensilla of the de sert locust and their responses to wind and to direct mechanical displ acement are described. The hairs on the external surfaces of the ventr al and dorsal ovipositor valves respond to wind stimulation, whereas t he hairs on the inner surfaces of the dorsal valves are not wind-sensi tive, All ovipositor hairs, however, respond to tactile displacement. Imposed tactile stimulation reveals two physiologically distinct types of ovipositor tactile hairs: the hairs on the inner surface of the do rsal valves are high-threshold hairs (threshold angular deflection of 26-67 degrees at 1 Hz) that respond phasically, whereas the hairs on t he lateral and ventral areas of the ventral valves and the lateral are as of the dorsal valves are low-threshold hairs (threshold angular def lection of 6-20 degrees at 1 Hz) that respond phasotonically. There is no apparent difference in the length of the two physiologically disti nct types of hairs, Both high- and low-threshold hairs are directional ly sensitive, with maximal responses to proximal deflection, towards t he abdomen, and are also velocity-sensitive. High-threshold hairs have velocity thresholds of 40-50 degrees s(-1) for some hairs and 110-140 degrees s(-1) for others for a deflection angle of 35 degrees, wherea s low-threshold hairs have lower velocity thresholds of less than 5 de grees s(-1) for the same deflection. High-threshold hairs adapt rapidl y to repetitive stimulation after as few as four cycles of stimulation at 0.5 Hz, Low-threshold hairs continue to respond after 40 cycles of stimulation at 0.5 Hz and show little adaptation to repetitive stimul ation at frequencies ranging from 0.1 to 5 Hz. Low-threshold hairs res pond with bursts of spikes at frequencies that reflect both the veloci ty and the duration of the stimulus. Furthermore, low-threshold hairs show little adaptation after 30 min of stimulation that simulates ovip osition digging, It is suggested (a) that low- and highthreshold ovipo sitor hairs detect phasic wind and/or tactile stimuli in non-ovipositi ng locusts and (b) that low-threshold hairs can also signal rhythmic t actile inputs during oviposition digging.