North American hymenopteran parasitoids of emerald ash borer larvae: seasonal abundance and interaction with introduced Asian parasitoids

In Michigan, United States of America, where Asian parasitoids were released to manage emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), we monitored four native parasitoids that also attack the invasive beetle – Atanycolus cappaerti Marsh and Strazanac, A. simplex (Cresson), and Spathius laflammei Provancher (all Hymenoptera: Braconidae), and Phasgonophora sulcata Westwood (Hymenoptera: Chalcididae) – using yellow pan traps and tree dissections. Adult A. cappaerti, followed by A. simplex, had the broadest seasonal activity, S. laflammei was captured primarily in the first half of the growing season, and P. sulcata was restricted to mid-summer. Adult abundances of native species varied among years but, except for P. sulcata, were never significantly lower than the established Asian emerald ash borer larval parasitoids, Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) and Spathius galinae Belokobylskij and Strazanac (Hymenoptera: Braconidae). Densities of emerald ash borer larvae parasitised by A. cappaerti or P. sulcata did not differ significantly from those of the two Asian species. Although adult A. simplex and S. laflammei were frequently captured, we did not confirm parasitisation of any emerald ash borer larvae by these two species, suggesting that they rarely attack emerald ash borer. We did not find any negative correlations between adult or immature parasitoid abundance of any parasitoid species, suggesting that any interspecific competition that may be occurring is negligible.