Factors Affecting Overwintering Success Of Spathius Galinae, A Parasitoid Of The Invasive Emerald Ash Borer (Agrilus Planipennis)

Abstract

Spathius galinae Belokobylskij is one of a few parasitoid wasps used as a biocontrol agent against the invasive emerald ash borer (Agrilus planipennis Fairmaire), a destructive beetle that has killed tens of millions of ash trees in the U.S. S. galinae are known to overwinter as prepupae in silken cocoons, but little is known about the overwintering success of these parasitoids at earlier life stages. Logs containing three different life stage treatments of S. galinae (early instar larva, mid instar larva, and prepupa) were placed in jars and deployed in two different microhabitat sites (urban woods and mature woods). The logs were deployed in late fall, remained in the field through winter, then S. galinae emergence was recorded in spring. Parasitoids in the warmer urban site emerged an average of 14 days earlier than parasitoids in the cooler, shaded mature woods site. S. galinae from all three life stage treatments successfully emerged, although the exact effect of life stage on overwintering success is not completely clear. Researchers in the future can release S. galinae for biocontrol through mid and late fall, but another study should be conducted to determine if young larval S. galinae have any less overwintering success than prepupae.