APHID PARASITOID RESPONSES TO SEMIOCHEMICALS - GENETIC, CONDITIONED OR LEARNT

Parasitoid foraging behaviour is known to be influenced by interaction s of genetic, physiological, environmental and experiential factors. A lthough the role of genetics, learning and conditioning in determining responses to foraging cues has been studied in lepidopteran parasitoi ds, aphid parasitoids have been less intensively researched. Using the tritrophic system, Vicia faba - Acyrthosiphon pisum - Aphidius ervi, evidence for the role of genetics and learning in parasitoid foraging is presented, and the difficulty of differentiating between genetic re sponses and those conditioned during parasitoid development is discuss ed. Aphidius ervi responds to aphid sex pheromones both in the field a nd in the laboratory. Since laboratory reared individuals have never e xperienced sexual aphids, the response must be genetic as it cannot ha ve been conditioned during development. An example of a response condi tioned during development is the variable response of A. rhopalosiphi to different wheat cultivars depending upon host feeding. Aphid parasi toids also are adept at learning as shown by their responses to plant- derived cues which are learnt as Conditioned Stimuli (CS). Host produc ts such as honeydew, as well as the host itself, can act as the Uncond itioned Stimulus (US) in the learning process. Aphidius ervi offers a good model for investigating the role of these factors in parasitoid f oraging behaviour. Finally, the value of such research for biological control programmes involving aphid parasitoids is discussed.