The foraging strategy of Diaeretiella rapae. I. The concept of the elementary unit of foraging.

The searching behaviour of Diaeretiella rapae, the main parasitoid of the cabbage aphid Brevicoryne brassicae, was analysed using whole Brussels sprouts plants. Diaeretiella directed its search on the plant: areas where aphids, or cues indicating their presence, were most expected were preferentially searched, and honeydew secreted by the aphids was used by the wasp as a kairomone for host location. The spatial configuration of the plant and the distribution of aphids and their cues on it have served as a template on which the Diaeretiella foraging strategy has been moulded by natural selection. The individual plant is thus an 'elementary unit of foraging' within the wasp environment.-from Author