Dynamics of Behavioural Phase Change in the First-Instar Nymphs of the Desert Locust Schistocerca gregaria (Forskål)

Using logistic regression analysis dynamics of the behavioural phase change in the first-instar nymphs of Schistocerca gregaria (Forskal) has been estimated. Insects belonging to two extreme phases were found to behave in a strikingly different manner. Moreover, the solitary-reared nymphs were found to retain certain degree of inherent gregariousness despite isolated rearing for a period of five days after hatching, whilst the crowd-reared counterparts became more gregarious over the same period of time. The results clearly demonstrate a trans-generational carry-over effect of phase in locusts where the previous phase history of the parents was found to have a profound effect on the behaviour of individual offspring nymphs. Relevance of this finding to field population has been discussed.