Role of olfactory and visual cues in the attraction/repulsion responses toconspecifics by gregarious and solitarious desert locusts

Desert locusts [Schistocerca gregaria Forskal (Orthoptera, Acrididae)] chan ge phase in response to population density: solitarious insects avoid one a nother, but when crowded they change to the gregarious phase and aggregate The attraction/repulsion responses of gregarious and solitarious locusts ma intain phase differences in locust populations. Despite considerable resear ch, the cues for aggregation fire poorly understood; moreover; the repulsio n response of solitarious locusts has not previously been investigated. Thi s study analyzes the role of visual and olfactory stimuli in triggering the se different responses to conspecifics. Isolation-reared insects were repel led by both olfactory and visual stimuli from other locusts. Crowd-reared i nsects were attracted by the combination of olfactory and visual cues. In a ddition olfactory stimuli affected other behaviors in both phases, and beha vioral differences between isolation and crowd-reared locusts were clear ev en in the absence of conspecifies. The sensory and neurological mechanisms underlying these responses are not well understood and will form the basis for neurobiological investigations of locust phase.