EFFECTS OF 5TH-INSTAR VOLATILES ON SEXUAL-MATURATION OF ADULT DESERT LOCUST SCHISTOCERCA-GREGARIA

The effect of the presence of gregarious fifth-instar nymphs on the se xual maturation of newly molted gregarious immature adult males and fe males of the desert locust S. gregaria was investigated by monitoring color changes (yellowing of body), sexual activity, aggregation-matura tion pheromone titers (as measured by phenylacetonitrile levels in mal es), oocyte length, and oviposition time. Maturation was significantly delayed in adults that were reared together with fifth-instar nymphs (visual, tactile, and chemical signals present) with respect to all pa rameters measured. Male and female nymphs were equally effective in in ducing this delay. Nymphs kept in an upper compartment of two-chamber cages (no visual or tactile contact possible) were similarly effective , but their feces were ineffective, suggesting the mediation of a vola tile signal from the nymphs themselves. This was confirmed by examinin g the effect of volatiles trapped from nymphs and testing synthetic bl ends of previously identified nymphal aggregation pheromone components (C-6, C-8-C-10 aliphatic aldehydes and acids, guaiacol, and phenol) o n the sexual maturation of adults. These and previous studies suggest a dual role for nymphal volatiles as nymphal aggregants and adult matu ration retardants, similar to the adult volatiles that are known as ad ult aggregants and maturation accelerants. The results are discussed i n terms of the role of the two pheromone systems in synchronizing matu ration of the gregarious adults.