A Model of an Aphid Population--Three Adventures

Abstract

This paper describes three developments of our studies on aphid populations. A previous paper (Hughes & Gilbert 1968) described a population model of the cabbage aphid (Brevicoryne brassicae L.), its parasite (Diaeretus rapae Curtis), and other natural enemies. The model uses a physiological time-scale with aphid instar-periods as units. Here we put the model to work to examine (1) stochastic variation of population numbers, (2) the parasite's strategy and (3) a field test of the model's predictions for biological control. In the original model the development time of the mature parasite was given as nine aphid instar-periods. This was known to be rather too long, but, as the parasite had such scant effect on the aphid population, a more accurate estimate was not sought. No generally applicable value can be given because of the difference in the apparent temperature thresholds of parasite and aphid (Hughes 1963), but at the ambient temperatures of the local populations, parasite development lasting 71-8 instar periods is more realistic.