Juvenile-hormone-mediated plasticity of aggregation behaviour and olfactory processing in adult desert locusts

In desert locusts Schistocerca gregaria, aggregation behaviour is elicited by aggregation pheromones. In this study, we show that the behavioural resp onse to the major and most potent adult aggregation pheromone component, ph enylacetonitrile, is age- and juvenile-hormone-dependent. Furthermore, we s how that juvenile hormone influences the responsiveness of olfactory intern eurons in the antennal robe to aggregation pheromone, whereas the responsiv eness of antennal receptor neurons is not changed. Old locusts and locusts injected with juvenile hormone, in contrast to young locusts and locusts de prived of juvenile hormone through allatectomy, i.e. after surgical removal of the gland producing this hormone, do not display any aggregation behavi our, as indicated by longterm behavioural observations. The lack of positiv e olfactory-guided behaviour coincides with an impairment of the central ol factory system, which displays a lower number of neurons responding to aggr egation pheromone. Indirect and direct actions of juvenile hormone at diffe rent levels of the central nervous system may thus contribute to the regula tion and modulation of behavioural responsiveness in the locust.