Reproductive and behavioral consequences of nutritional stress on two Braconid classical biological control agents of the emerald ash borer

Emerald ash borer (Coleoptera: Buprestidae: Agrilus planipennis Fairmaire; EAB) is an invasive pest that threatens ash trees (Fraxinus spp.) in managed and unmanaged forests throughout North America and Europe. Since its introduction, EAB has killed hundreds of millions of trees, resulting in severe ecological and economic damage exceeding 11 billion dollars. Classical biological control uses natural enemies introduced from the pest’s native range to reduce their populations. Specialist parasitoid wasps in the genus Spathius have been introduced as classical biocontrol agents of EAB. Detection and response to volatiles emitted by ash foliage act as long-range attractants critical for parasitoids to locate and parasitize EAB. The physiological state of parasitoids, may vary under different environmental conditions, has been predicted to alter their host-location behaviors. However, how differences in physiological conditions impact parasitoid’s survival, egg count, and ability to detect and respond to host-associated cues is poorly known. We evaluated how adult feeding influences survival and mature eggs of Spathius agrili and Spathius galinae. Fed wasps had significantly higher survival and more mature eggs compared to starved wasps. The response of wasps towards foliage of young and old green ash trees was tested in a four-arm olfactometer under varying physiological conditions. Wasps were fed or starved prior to bioassays. Both parasitoid species can detect and respond to trees of different ages, but physiological condition altered host preferences. This study will contribute to classical biological control by understanding the physiological aspects of natural enemies, impacting establishment and parasitism rates across a heterogeneous landscape.