A behavioural analysis of phase change in the desert locust

Sj. Simpson et al., A behavioural analysis of phase change in the desert locust, BIOL REV, 74(4), 1999, pp. 461-480
Citations number
Categorie Soggetti
Biology,"Experimental Biology
Journal title
ISSN journal
1464-7931 → ACNP
Year of publication
461 - 480
SICI code
A programme of research into phase change in the desert locust, Schistocerc a gregaria, is described. The ability to change phase between solitarious a nd gregarious forms in response to population density is a key feature of l ocusts and is central to their occasional yet catastrophic impact on humans . Phase polymorphism is an extreme form of phenotypic plasticity. The most labile phase characteristic is behaviour. It is argued that a fully integra ted study of behavioural phase change provides a powerful tool for understa nding both the mechanisms of phase change and locust population dynamics, b oth of which offer possibilities for improved management and control. of de sert locust plagues. An assay for measuring behavioural phase-state in indi vidual locusts was derived, based on logistic regression analysis. Experime nts are described that used the assay to quantify the time-course of behavi oural change, both within the life of individual locusts and across generat ions. The locust-related stimuli that provoke behavioural gregarization wer e investigated. Complex interactions were found between tactile, visual and olfactory stimuli, with the former exerting the strongest effect. Behaviou ral analysis also directed a study of the mechanisms whereby adult females exert an epigenetic influence over the phase-state of their developing offs pring. Female locusts use their experience of the extent and recency of bei ng crowded to predict the probability that their offspring will emerge into a high-density population, and alter the development of their embryos acco rdingly through a gregarizing agent added to the foam that surrounds the eg gs at laying. There is also a less pronounced paternal influence on hatchli ng phase-state. An understanding of the time-course of behavioural phase ch ange led to a study of the effect of the fine-scale distribution of resourc es in the environment on interactions between individual locusts, and hence on phase change. This, in turn, stimulated an exploration of the implicati ons of individual behavioural phase change for population dynamics. Cellula r automata models were derived that explore the relationships between popul ation density, density of food resources and the distribution of resources in the environment. The results of the simulation showed how the extent of gregarization within a population increases with rising population size rel ative to food abundance and increasing concentration of food resources. Of particular interest was the emergence of critical zones across particular c ombinations of resource abundance, resource distribution and population siz e, where a solitarious population would rapidly gregarize. The model provid ed the basis for further laboratory and field experiments, which are descri bed.