Incubation and overwintering in the egg stage of the African migratory locust,Locusta migratoria migratorioides(Orthoptera: Acrididae), on the highveld of South Africa

Abstract Incubation of eggs of the African migratory locust,Locusta migratoria migratorioides(Reiche & Fairmaire), was examined in the Orange Free State (OFS) highveld of South Africa where the locust is a recurring pest of cereal crops. A minimum incubation time of 16±SE 0.97 d was recorded in summer and this progressively increased through autumn as temperatures declined. Eggs laid in autumn overwintered for 140±2.63 d until spring, when rising temperatures initiated hatching. Controlled laboratory studies established that the threshold for egg development was in the region of 15.6°C and that eggs required 5268 degree-hours to complete their development. Analysis of hourly soil temperature records, measured at egg pod depth in the field, showed that temperatures first dropped below this critical temperature threshold during mid-April, after which eggs became quiescent and overwintered until spring. There was no evidence of diapause in the field and overwintering eggs exhibited a wide range of embryonic development. Quiescence during winter on the OFS highveld was therefore a simple temperature-induced response. This is the first record of prolonged overwintering in the egg stage of the migratory locust in Africa.