Assessing the impact of physiological condition on the response of two biological control agents of the emerald ash borer to a known attractant

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 utilizes 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 is critical for parasitoids to locate EAB. The physiological state of parasitoids, which may vary under different environmental conditions, has been predicted to alter their host-location behaviors. However, how differences in physiological conditions impact a parasitoid’s ability to detect and respond to host-associated cues is poorly known. We evaluated how adult feeding influences the attraction of Spathius agrili and Spathius galinae towards foliage of young and old green ash trees in a four-arm olfactometer. Wasps were fed or starved prior to bioassays. Both parasitoid species can detect and respond to trees of different ages, but starvation alters host preferences. The study will contribute to classical biological control by understanding how natural enemies under differing physiological conditions forage differently towards the foliage of young and old trees of ash, impacting the likelihood of their establishment and parasitism rates across the heterogeneous landscape.