Feasibility of egg releases in establishing Laricobius populations on eastern hemlock

Hemlock woolly adelgid (Adelges tsugae, HWA) is a pest of eastern (Tsuga canadensis) and Carolina (T. caroliniana) hemlock in the eastern U.S. Species of the predatory beetle Laricobius (L. nigrinus and L. osakensis) have been released to manage the winter generation of populations of HWA and have established in many areas. While considered a successful biological control agent, rearing of Laricobius spp. is laborious and time consuming. Additionally, lab-reared pupating and aestivating Laricobius experience mortality up to 70% during the summer months. One solution to reduce the amount of infested hemlock needed to rear Laricobius spp. and labor involved attempting to sustain large colonies over the summer is to release Laricobius eggs rather than adults. Releasing Laricobius eggs during the winter months would reduce the amount of food material needed to maintain a colony. This study investigates the effectiveness of egg releases as a viable method to establish Laricobius spp. in release sites. Eggs were released on study trees in February and March 2022, and soil emergence cages were deployed September 2022 and monitored weekly to assess emergence of Laricobius spp. under canopies of study trees. Laricobius emerged from 20 October 2022 to 27 January 2023. Emergence trends and population densities will be discussed. This study is being repeated 2023-2024.