A diet of senescent Brassica spp. delayed sexual maturation in the desert locust. The senescent leaves were shown to be short of gibberellins, and a dietary supplement of gibberellin A3 (1 microgram per locust per day) restored the rate of maturation to that found in animals feeding on green leaves. An external application of eugenol had a similar effect. The sexual immaturity of desert locusts during the dry season may result from the senescent condition of their desert food plants.