Interspecific Competition Between Idiobiont Larval Parasitoids of Emerald Ash Borer

Abstract

New associations between parasitoid species is common in biological control with interactions ranging from coexistence to competitive exclusion. Spathius agrili and Spathius galinae, native to North East Asia, are two host-specific idiobiont larval parasitoids of the invasive emerald ash borer Agrilus planipennis that do not overlap in their native ranges but have been recently introduced to the United States for biocontrol of A. planipennis. We conducted laboratory experiments to determine the results of competition between these two species. Competition between parasitoid larvae on a single host (intrinsic competition) and competition between adult parasitoids for oviposition sites (extrinsic competition) were evaluated. Successful multiparasitism did not occur in any intrinsic trials. Extrinsic competition favored S. agrili, but S. galinae was not excluded. Competition lowered parasitism rates for both species, but overall parasitism was not lowered.