Historic Assessment and Analysis of the Mass Production ofLaricobiusspp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid, at Virginia Tech

Abstract

Laricobius nigrinus (Coleoptera: Derodontidae) Fender and Laricobius osakensis (Coleoptera: Derodontidae) Montgomery and Shiyake have been mass produced by Virginia Tech as biological control agents for the hemlock woolly adelgid (HWA), Adelges tsugae (Hemiptera: Adelgidae) Annand, for the past 15 and 9 yr, respectively. Herein, we describe modifications of our rearing procedures, trends and analyses in the overall production of these agents, and the redistribution of these agents for release to local and federal land managers. Based on these data, we have highlighted three major challenges to the rearing program: 1) high mortality during the subterranean portion of its life cycle (averaging 37% annually) reducing beetle production, 2) asynchrony in estivation emergence relative to the availability of their host HWA minimizing food availability, and 3) unintended field collections of Laricobius spp. larvae on HWA provided to lab-reared larvae complicating rearing procedures. We further highlight corresponding avenues of research aimed at addressing each of these challenges to further improve Laricobius spp. production.

Subterranean Survivorship and Seasonal Emergence ofLaricobiusspp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid

“…Lariocobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae) and Laricobius nigrinus Fender (Coleoptera: Derodontidae) have been used as classical biological control agents against HWA, in the eastern United States, for the past 9 and 17 years, respectively (Mayfield et al 2020, Foley et al 2021. Laricobius rubidus LeConte (Coleoptera: Derodontidae) is the only Laricobius species endemic to eastern North America.…”

“…Both eastern white pine and eastern hemlock and their respective Adelgid species often occur sympatrically. Because L. rubidus can be found in association with L. nigrinus at low proportions on HWA infested hemlock in the field, as it is collected for food, they are often unintentionally introduced into the laboratory colony (Fischer et al 2015, Foley et al 2021.…”

“…However, in laboratories where Laricobius spp. are reared, adult emergence has consistently been noted to occur as early as mid-June for both L. nigrinus and L. osakensis (Foley et al 2021).…”

“…Deployment of L. nigrinus and L. osakensis for biological control of HWA has occurred through laboratory mass production efforts by universities and governmental agencies (Foley et al 2021), and through field collection and redistribution of L. nigrinus (McDonald et al 2011). Laricobius nigrinus has been released throughout most of the HWA-infested range of eastern hemlock and continues to spread from those original release sites to new locations (Toland et al 2018, Foley et al 2019, Virginia Tech 2019.…”

“…Historically, the mass production of these agents at Virginia Tech's insectary and other rearing facilities have been consistently limited by two factors: high colony mortality (63%) during the subterranean phase, and early emergence of adult beetles before suitable prey (HWA nymphs that have broken aestivation) are available in the fall (Foley et al 2021). It is unknown if the low subterranean survivorship and early emergence seen in the mass rearing laboratories are artifacts of the rearing process, or if they are characteristic of their field biology in the introduced range.…”