Cold tolerance of emerald ash borer parasitoids: Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), Spathius agrili Yang (Hymenoptera: Braconidae), and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae)

Abstract

Three Chinese parasitoids are currently being released in North America to control emerald ash borer, <italic>Agrilus planipennis </italic>Fairmaire (Coleoptera: Buprestidae): <italic>Spathius agrili</italic> Yang (Hymenoptera: Braconidae), <italic>Tetrastichus planipennisi</italic> Yang (Hymenoptera: Eulophidae), and <italic>Oobius agrili</italic> Zhang and Huang (Hymenoptera: Encyrtidae). The degree to which cold climates may limit their potential distributions in North America is unknown, especially in areas like Minnesota that experience a wide range of winter temperatures. To assess parasitoid cold tolerance, I developed a new thermocouple design to reliably measure the temperature of small insects, such as parasitoids. I then exposed the parasitoids to temperatures from 0 to -35&deg;C in the lab to assess their cold tolerance. NAPPFAST software was used to forecast overwintering mortality of <italic>S. agrili</italic> and <italic>T. planipennisi</italic> in North America. These forecasts of overwintering mortality will aid researchers and policy makers in deciding where the parasitoids should be released.