INFLUENCE OF PLANT QUALITY ON INTERACTIONS BETWEEN THE APHID PARASITOID EPHEDRUS CALIFORNICUS BAKER (HYMENOPTERA: APHIDIIDAE) AND ITS HOST, ACYRTHOSIPHON PISUM (HARRIS) (HOMOPTERA: APHIDIDAE)

Abstract

AbstractWe determined variations in selected life-history parameters in a tritrophic system that consisted of a plant (broad bean, Vicia faba L.), an aphid (pea aphid, Acyrthosiphon pisum), and an aphid parasitoid (Ephedras californicus). We manipulated plant and aphid quality by growing bean plants in a high- and a low-quality nutrient solution for three generations. Pea aphids adapted to reduced nutrient availability by differentially allocating resources to somatic and gonadal growth across generations. On low-quality plants, time from birth to adult increased and dry mass decreased. The number of sclerotized embryos was correlated with adult dry mass. By contrast, in E. californicus, variations in dry mass, rate of development, and number of ovarial eggs did not suggest transgenerational adaptations to resource quality as measured by aphid size. The number of mature eggs was dependent on female age. Development time varied with parasitoid sex and was independent of aphid stage at the time of death. In the low-quality treatment, males survived on average longer than females eclosing from the same kinds of hosts.Aphids and their parasitoids have evolved flexible life-history strategies in response to variations in plant quality. Pea aphids adapted to qualitatively variable resources by optimizing the balance between somatic and gonadal investment across successive generations. But E. californicus responded to low host quality at the level of the individual, rather than across generations; the trade-off pattern was influenced by the host’s growth potential after parasitization.