Journal of Chemical Ecology, Vol. 23, No. 5, 1997 EFFECTS OF FIFTH-INSTAR VOLATILES ON SEXUAL MATURATION OF ADULT DESERT LOCUST Schistocerca gregaria YOUSIF O. H. ASSAD, 1 AHMED HASSANALI, 1 '* BALDWYN TORTO, 1 HASSANE MAHAMAT, 1 NABIL H. H. BASHIR, 2 and SAYED EL BASHIR 1 'International Center of Insect Physiology and Ecology, (ICIPE) P.O. Box 30772, Nairobi, Kenya ^Environment and Natural Resources Research Institute, (ENRRI) The National Center for Research P. O. Box 6090, Khartoum, Sudan (Received May 14, 1996; accepted January 6, 1997) Abstract—The effect of the presence of gregarious fifth-instar nymphs on the sexual maturation of newly molted gregarious immature adult males and females of the desert locust S. gregaria was investigated by monitoring color changes (yellowing of body), sexual activity, aggregation-maturation phero- mone titers (as measured by phenylacetonitrile levels in males), 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 parameters measured. Male and female nymphs were equally effective in inducing this delay. Nymphs kept in an upper com- partment of two-chamber cages (no visual or tactile contact possible) were similarly effective, but their feces were ineffective, suggesting the mediation of a volatile signal from the nymphs themselves. This was confirmed by examining the effect of volatiles trapped from nymphs and testing synthetic blends of previously identified nymphal aggregation pheromone components (C 6 , C 8 -C| 0 aliphatic aldehydes and acids, guaiacol, and phenol) on the sexual maturation of adults. These and previous studies suggest a dual role for nymphal volatiles as nymphal aggregants and adult maturation retardants, similar to the adult volatiles that are known as adult aggregants and maturation accelerants. The results are discussed in terms of the role of the two phero- mone systems in synchronizing maturation of the gregarious adults. *To whom correspondence should be addressed. 1373 0098-0331/97/0500-1373$l2.50/0 © 1997 Plenum Publishing Corporation