Time-course haemolymph juvenile hormone titres in solitarious and gregarious adults of Schistocerca gregaria, and their relation to pheromone emission, CA volumetric changes and oocyte growth

The haemolymph JH III titres in solitarious and gregarious adult desert locusts, Schistocerca gregaria, were examined in relation to corpus allatum (CA) volumes, aggregation–maturation pheromone production in males and oocyte growth in females. The JH titres of gregarious females were generally higher than those of solitarious females at all ages studied. The titre patterns, however, were similar: relatively high on day 10, dropping to low levels between days 20 and 25, before rising again by day 25. In the solitarious males, the JH titre was very low on day 10 after fledging, but increased gradually and reached a maximal amount on day 30. The JH titre in gregarious males was low on day 10, elevated on day 15 coinciding with the start of the production of the pheromone, and dropped to a relatively low level on day 20 around the time of maximal pheromone production, then rising again by day 25. These results suggest that biosynthesis of the pheromone is associated with a high JH titre peak in the haemolymph. Although a clear relationship was found during the first gonadotropic cycle between JH titres, on one hand, and CA volume and oocyte growth, on the other, in both phases, no such correlation could be discerned in the second cycle.