Reproduction and optimal foraging in the parasitoid wasp Trichogramma kaykai

For some animals optimal foraging and reproduction are linked. A classic example of this linkage is found in parasitic wasps that complete development inside host organisms.  We studied one such wasp Trichogramma kaykai, an egg parasitoid of the Mormon Metalmark butterfly, Apodemia mormo. For T. kaykai the foraging and reproductive environment primarily consists of patches of individual host eggs. Female foundress wasps measure host eggs, choose how many eggs to oviposit, and then continue foraging for additional hosts. Optimal foraging predicts that a foundress will maximize host utilization per unit time. The resulting F1 generation per host may have variable fitness contingent on brood size thus influencing ovipositing behavior. Field-collected parasitized A. mormo eggs showed variation for T. kaykai brood size, suggesting alternative reproductive/foraging strategies. Two brood size (n = 4, 5) groups of thirty broods each were collected from the Mojave Desert. A. mormo host eggs were measured for size variation. Broods were supplied with nourishment and host eggs (Ephestia kuehniella) for two days. The F2 generation was assessed for total wasps emerged, females emerged, pupal stage wasps, and proportional fitness. We found no fitness differences between alternative reproductive strategies and no indication of host egg size-proportional fitness covariance. This suggests that individual offspring/brood fecundity for the two brood size groups examined is not influencing foundress oviposition behavior, however, in the highly variable natural environment other selective pressures may impact actual brood fitness. Further research is needed to determine additional factors influencing T. kaykai reproductive optimal foraging decisions.