An analysis of the behavioural effects of crowding and re‐isolation on solitary‐reared adult desert locusts (Schistocerca gregaria) and their offspring

Abstract

Abstract. The time‐course of behavioural change in response to crowding and re‐isolation was investigated in adults of Schistocerca gregaria Forskål (Orthoptera, Acrididae) using logistic regression analysis. Crowding solitary‐reared adults for a period of 4 h caused them to behave similarly to crowd‐reared insects, with their becoming much more active and moving towards rather than away from a stimulus group of locusts. Responsiveness to crowding was greatest in young adults. The behaviour acquired after 48 h of crowding was lost within 1 day of re‐isolation. Although experience by solitary‐reared adults of crowding for 48 h had only transitory effects on their own behaviour, there was also a long‐term influence on the behaviour of their offspring. The strength of this effect was dependent on the age at which adults experienced crowding, increasing in a graded manner with adult age, and hence the recency of crowding before oviposition. Parents crowded at a late stage in the reproductive cycle yielded hatchlings which behaved indistinguishably from those from crowd‐reared adults. Such an effect is consistent with the idea that females, through their previous experience of crowding, are effectively predicting the probability that their offspring will emerge into a high‐density population, and predisposing their hatchlings' behaviour accordingly.