The importance of adult food for parasitoids

The importance of adult food for parasitoids has been recognized for decades. Numerous laboratory studies show that suitable food sources can substantially increase longevity and fecundity of adult hymenopteran and dipteran parasitoids (reviews: Heimpel et al. 1997; Lewis et al. 1998). It is now appreciated that the consumption of non-host food can influence many other aspects of parasitoid biology such as egg viability, diapause in progeny, foraging decisions, searching efficiency, the onset and rate of egg resorption, primary sex ratio of progeny, flight initiation, and timing of flight. As a consequence non-host food can affect parasitoid and host dynamics, competitive interactions and niche partitioning among parasitoid species, productivity in laboratory cultures, and the probability of parasitoid establishment in classical biological control (Jervis 1998). In those parasitoid species that resorb eggs, starved individuals generally have higher rates of egg resorption than well-fed individuals, but this is not always the case (Olson et al. 2000). Egg resorption may increase life expectancy at the cost of reduced or delayed reproduction, which in turn may increase the risk of predation or other mortality factors. Conversely, there is presumably a metabolic cost to increased egg maturation, which decreases life expectancy (e.g., Roitberg 1989). For species that do not resorb eggs (Olson et al. 2000), investing in reproduction rather than increased life expectancy may be a viable reproductive strategy, especially in host-rich habitats. In host-poor habitats, however, non-host food will be important to extend life expectancy.