Egg maturation, host feeding, and longevity in two Metaphycus parasitoids of soft scale insects

Abstract

We investigated several physiological and life history correlates of egg maturation in Metaphycus flavus Howard and Metaphycus luteolus Timberlake (Hymenoptera: Encyrtidae), parasitoids of soft scale insects (Hemiptera: Coccidae). Both parasitoid species emerge from their hosts without mature eggs and, hence, are strictly synovigenic. Given only a carbohydrate diet, they mature eggs which, after three days, are gradually resorbed until they have almost no eggs and finally die. Egg maturation rates are temperature dependent and are slower at lower temperatures. Both species host feed and the nutrients obtained appear to facilitate egg maturation. The size of a host meal also influences the number of eggs that females mature; both species mature more eggs when they feed on larger than smaller scales upon emergence. Starved wasps have very limited longevity and, when fed only water, die within two days. Body size explains little variation in female longevity and its influence depends on diet (carbohydrate and host meals versus carbohydrates only). Our results suggest that nutrients obtained from host feeding are differentially allocated to reproduction versus somatic maintenance in the two species. M. flavus uses more resources from its host meals for reproduction (egg maturation), whereas M. luteolus uses some of these nutrients for metabolic maintenance (longevity). Aspects of the ecology and foraging behavior of these wasps, and how they are related to biological control are discussed within the context of their egg maturation and host feeding physiology.