HOST-PLANT APHIDOPHAGA INTERACTIONS

Allelochemicals in the host plant can affect natural enemies adversely through the passage of plant toxins up the trophic pyramid. Additiona lly, the size of the host prey may be influenced through the plant, an d this in turn affects the size and fecundity of parasitoids. The nume rical response of natural enemies to prey density may also be affected by their attraction to plant volatiles, even in the absence of prey. Predators and parasitoids show different functional responses to prey on different host plants. This is related to prey size, to differences in defensive and other behaviours of the prey, and to effects on sear ching time of natural enemies. These influences are highly relevant to the use of host plant resistance as a pest control technique. The arg ument that natural enemies may accelerate the selection for plant-adap ted biotypes of herbivores, and the production of pest-resistant crop varieties by genetic engineering are modern challenges to the practica l exploitation of host plant-Aphidophaga interactions.