Responses of an Idiobiont Ectoparasitoid,Spathius galinae(Hymenoptera: Braconidae), to Host Larvae Parasitized by the Koinobiont EndoparasitoidTetrastichus planipennisi(Hymenoptera: Eulophidae): Implications for Biological Control of Emerald Ash Borer (Coleoptera: Buprestidae)

Abstract

Understanding interspecific competition among insect parasitoids is important in designing classical biological control programs that involve multiple species introductions. Spathius galinae Belokobylskij and Strazenac, a new idiobiont ectoparasitoid from the Russian Far East, currently is being considered for introduction to the United States for biological control of the emerald ash borer, Agrilus planipennis Fairmaire, whereas Tetrastichus planipennisi Yang, a koinobiont endoparasitoid native to China, is another natural enemy that already has been introduced in the same program. In a laboratory study, we examined the potential interactions between these two parasitoids when they compete for the same emerald ash borer host larvae. In multiple-choice assays where healthy emerald ash borer larvae were presented along with emerald ash borer larvae previously parasitized by T. planipennisi at different times, S. galinae attacked host larvae already parasitized by T. planipennisi for up to 4 d, but not 8 d. However, parasitism rates were significantly lower in previously parasitized hosts as compared with healthy host larvae. In no-choice tests where S. galinae females were presented either with healthy emerald ash borer larvae or emerald ash borer larvae parasitized by T. planipennisi at several earlier time points, S. galinae again parasitized significantly more healthy host larvae than T. planipennisi-parasitized larvae. These results suggest that the ectoparasitoid S. galinae can discriminate between healthy host larvae and T. planipennisi-parasitized larvae, and competitive interactions between the two parasitoids are likely to be minimal if coreleased by the emerald ash borer biological control program.