Tritrophic impacts of Bt-expressing transgenic pine on the parasitoid Meteorus pulchricornis (Hymenoptera: Braconidae) via its host Pseudocoremia suavis (Lepidoptera: Geometridae)

Pseudocoremia suavis is a New Zealand endemic geometrid present in commercial pine plantations where it has occasionally reached pest levels. It is parasitized by a self-introduced, generalist, solitary, braconid endoparasitoid, Meteorus pulchricornis. Tritrophic impacts on M. pulchricornis of transgenic pine, Pinus radiata, expressing Bacillus thuringiensis (Bt) Cry1Ac toxin, were examined using a laboratory-based system with P. suavis as the host. Unparasitized P. suavis fed with Bt-expressing pine foliage had significantly higher mortality than those fed with control pine and surviving larvae had reduced growth rates and delayed pupation. Parasitoid survival from Bt pine-fed hosts was reduced significantly when pre- and post-emergence survival was combined. Observed pre-emergence host mortality in parasitized Bt pine-fed P. suavis was consistent with the level of host mortality expected if parasitism, which itself caused significant pre-emergence host death, and the Bt toxin were acting independently as larval mortality factors. Parasitized hosts fed on Bt pine had significantly reduced growth rates and parasitoids took longer to emerge. The degree of developmental delay caused by Bt appeared to be greater for unparasitized hosts than for parasitoids. There was no effect of Bt on the parasitoid pupal duration, weight of pupa in cocoon, or number of eggs in F1 adults’ ovaries. Across both treatments, the number of days to parasitoid emergence was negatively correlated with host weight on parasitism day, and the number of eggs in F1 adults’ ovaries was positively correlated with cocoon weight.