OPTIMAL FORAGING IN LADYBIRD BEETLES (COLEOPTERA, COCCINELLIDAE) AND ITS CONSEQUENCES FOR THEIR USE IN BIOLOGICAL-CONTROL

A model optimizing the number of eggs laid in an aphid colony by an ad ult ladybird reveals that there exists an optimum number, which maximi zes the resulting offspring biomass. This remains true even if the mod el is expanded to include more than one adult ladybird and several aph id colonies. Adult ladybirds should not continue to aggregate in areas of aphid abundance (Kareiva & Odell, 1987), but should leave an aphid aggregate, even though the aphids are still increasing in abundance, as soon as a certain number of eggs are laid and/or larvae are present . If the ladybirds lay the optimal number of eggs, then their offsprin g have only a slight effect on the peak number of aphids.