Aspects of the behavior, ecology and evolution of a braconid parasitoid
Insects pass through several life-stages during development and, ultimately, individuals interact within populations. My research focused on the immature and adult stages of parasitoids. A final study considered the interactions of parasitoids with their hosts at the metapopulation level.
To complete development the host of an immature parasitoid must survive until the parasitoid is ready to pupate. Parastized hosts may be at a competitive disadvantage, when competing with unparasitized individuals, because parasitism influences aspects of host behavior and development. I investigated the factors influencing the survival of parasitized hosts (hence parasitoids) when hosts compete for resources. I found that Acrobasis vaccinii parasitized by Phanerotoma franklini were at a competitive disadvantage compared to unparasitized A. vaccinii. I then sampled wild bogs to determine if competitive interactions occur in the field. My findings indicated that local densities of insects were high and that resources may be limiting in local areas. Finally, I developed an individual-based model to examine how resource limitation and parasitism rate influence the level of mortality caused by competition. The model suggested that the parasitism rate and level of resource availability interact to determine the level of mortality experienced by parasitized and unparasitized larvae.
Next, I examined the adult food foraging behavior of P. franklini . I determined that adult feeding significantly influenced adult lifespan and increased egg maturation. Subsequent studies found that the food sources used by this parasitoid were likely to be located in close vicinity to hosts and that substances leached to the surface of cranberry foliage may be a primary food source for the parasitoid. Feeding on leached substances did not reduce foraging efficiency in later laboratory tests.
I constructed a deterministic real-number model and a stochastic individual-based model to examine the role of space in the evolution of host resistance and parasitoid virulence. The individual-based model demonstrated substantial structuring of resistance traits in space when the movement rate of the host and parasitoid was low, while the deterministic model did not. I suggest that the inclusion of stochastic movement and extinction in the individual-based model resulted in the structuring of resistance traits in space. Consequently, the extinction of parasitoids in patches was common, and resulted in periods of selection against resistance.