Subterranean survivorship and seasonal emergence of laricobius spp. (Coleoptera: Derodontidae), biological control agents for the hemlock woolly adelgid.

Abstract

Following the adventive arrival, subsequent spread, and ensuing impact of Adelges tsugae Annand (Hemiptera:Adelgidae), the hemlock woolly adelgid (HWA) in the eastern United States, a robust initiative was launched with thegoal of decreasing ecosystem impacts from the loss of eastern hemlock (Pinales: Pinaceae). This initiative includesthe use of biological control agents, including Laricobius spp. (Insecta: Coleoptera). Laboratory production of theseagents is limited by subterranean mortality and early emergence. Therefore, the subterranean survivorship andtiming of emergence of a mixture of Laricobius spp. was investigated. PVC traps internally lined with a sticky cardand covered with a mesh screen were inserted into the soil to measure the percent emergence of adults based on thenumber of larvae placed within. The number of emerged adults in the field and laboratory-reared larval treatmentswas adjusted based on emergence numbers in the control and used as the response variable. Independent variablesincluded in the final model were: treatment (field-collected vs. laboratory-reared), organic layer depth (cm), soil pH,and April-to-December mean soil moisture. No differences were found in survivorship between field-collected andlaboratory-reared treatments. As pH and organic layer increased survivorship decreased, significantly. Althoughthe majority of emergence occurred in the fall, emergence also occurred in spring and summer. The occurrence ofspring and summer emergence and low survivorship (17.1 ± 0.4%) in the field across all treatments suggests thatthese are characteristics of Laricobius spp. field biology in their introduced range and not artifacts of the laboratoryrearing process.

Citation

Foley, Jeremiah R; McAvoy, Thomas J; Grubb, Christopher; Mayfield, Albert E; Strahm, Brian; Salom, Scott M. 2021. Subterranean survivorship and seasonal emergence of Laricobius spp. (Coleoptera: Derodontidae), biological control agents for the hemlock woolly adelgid . Environmental Entomology. 51(1): 63-70. https://doi.org/10.1093/ee/nvab124.