Chancing oviposition preferences of the desert locust, Schistocerca gregaria, suggest a strong species predisposition for gregarization

Field sun cys at Eve sites within desert locust breeding habitats around Po rt Sudan during three successive seasons indicated that early in the rainy season the incoming solitary females oviposited predominantly in the vicini ty of Heliotropium spp. (similar to 66%) and millet (similar to 32%) seedli ngs. Solitary nymphs also preferred to feed on these plants Follow-up cage experiments were conducted in the held in which solitary and gregarious fem ale locusts were presented with choices of selected desert plants and egg p ods. When presented with bulrush miller, Heliotropium spp, Zygophyllum simp lex, and untreated moistened sand, solitary females oviposited adjacent to the first two plants (40% and 60%, respectively). However, when offered a c hoice of either or both of these plants together with egg pods derived from gregarious and/or solitary insects, solitary females showed a significantl y higher preference for ovipositing near gregaria egg pods than near the pl ants, with solitaria egg pods eliciting the least response. In contrast wit h solitary females and in the absence of gregaria egg pods, gregarious fema les preferred to oviposit in untreated moist (control) sand (74-77%) away f rom the plants (6-14%) or solitaria egg pads (similar to 4%). However, when present, gregaria egg pods elicited significantly more oviposition. These and previous results indicate a hierarchy of phase-dependent oviposition pr eferences in the desert locust and are interpreted in terms of a strong pro pensity of the species to exploit opportunities under appropriate condition s to facilitate congregation and the gregarization of the progeny.