Separating the effects of experience, size, egg load, and genotype on host response in Trichogramma (Hymenoptera: Trichogrammatidae)

The effects of experience, egg load, and wasp size on the response of four strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae) to three economically important hosts, Heliothis punctigera (Noctuidae), Phthorimaea opercullela (Gelechiidae), and Sitotroga cereallela (Gelechiidae) were investigated. Experience effects due to rearing host and oviposition were considered in all combinations of host species. Both these effects altered response levels to low-ranked hosts but not to highly preferred hosts. Size was correlated with host response in some strains; larger females took more encounters with a host before accepting it, while egg load was not correlated with number of host encounters. However, egg lend, rearing host, and size all affected acceptance of the low-ranked host S. cereallela. Females were more likely to accept this host if they were reared on S. cereallela, had a small size, and had a high egg load. Effects were consistent across strains, although overall acceptance levels differed among strains.