Ecological mechanisms for non-target parasitism by the Moroccan ecotype of Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in native grassland

Abstract

The Moroccan ecotype of the braconid parasitoid Microctonus aethiopoides was introduced into New Zealand for biological control of the lucerne pest Sitona discoideus. The parasitoid also attacks several non-target native weevil species found in pasture and also to a lesser extent in native tussock grassland. We carried out a series of laboratory and field experiments, and population modelling to investigate whether the parasitoids were established at low levels on native weevils in tussock grassland, whether S. discoideus was able to survive and support parasitoid development away from lucerne, its normal host plant, or whether parasitism was occurring as a result of spillover from agricultural environments. We found that S. discoideus was able to survive and support parasitoid development on white clover which is commonly found in native grassland. However, the levels of parasitism in weevil species in tussock grassland appeared to be constrained, at least in part, by low temperatures limiting the number of parasitoid generations possible per year and by the frequency of sub-zero temperatures that caused pupal mortality. Projected climate change might reduce this constraint and the implications of this are discussed.