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

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 the goal of decreasing ecosystem impacts from the loss of eastern hemlocks, Tsuga canadensis (L.) This initiative includes the use of biological control agents, specifically Laricobius spp. The mass-production of these agents in the lab is limited by two primary factors: 1) subterranean mortality and 2) subterranean early emergence. We investigated the subterranean survivorship and timing of emergence of Laricobius spp. at six field sites for two consecutive years. PVC tubes were internally lined with a sticky card and covered with a screen and were inserted into the soil and used to assess the proportion of adults emerging. The independent variables considered were: two rearing techniques (laboratory-produced and field-collected) and a control (no larvae), trial years, organic matter depth, and April-to-December mean soil moisture. The proportion of survivorship from laboratory and the field reared Laricobius spp. was 19.8 and 17.8%, respectively. We found no difference when comparing rearing technique, but did to the control. We also found that as moisture increased and organic matter decreased, survivorship increased. Although the majority of emergence occurred as expected in the fall, emergence also occurred in spring and summer. Spring emergence occurred across all treatments and we observed relatively low survivorship. Results suggest that low survivorship is not an artifact of the rearing process and is a part of their natural biology.