Abstract
The hemlock woolly adelgid (HWA) is an invasive insect species native to Japan causing significant hemlock mortality in the eastern United States. Laricobius spp. have been targeted as biological control agents because they are adelgid specialists. Laricobius osakensis Montgomery and Shiyake is native to the same region of Japan from which the strain of HWA found in the eastern United States originated. Studies in Japan found that it is phenologically synchronous with HWA. Following approval to release L. osakensis from quarantine in 2010, approximately 32,000 were released at a total of 61 sites starting in 2012. In winter of 2014 and 2015, periods of extreme cold temperatures throughout the eastern USA, as well as the polar vortex, resulted in extensive mortality to HWA, which likely delayed the establishment of L. osakensis. The ability of the beetle to survive and establish in the eastern United States is reported here. In the first year of this study (2015–2016), limited numbers of L. osakensis were recovered, as HWA populations were still rebounding. In the second year (2016–2017), 147 L. osakensis were collected at 5 of 9 sites sampled, coinciding with rebounding HWA populations. Larval recovery was much greater than adult recovery throughout the study. HWA density was directly correlated with warmer plant hardiness zones and recovery of Laricobius beetles was significantly correlated with HWA density. Our results suggest that L. osakensis is successfully establishing at several of the sampled release sites and that the best predictor of its presence at a site is the HWA density.
Highlights
The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), an insect pest native to Asia and the western United States, is causing significant mortality to eastern and Carolina hemlock trees in the eastern United States [1]
This study focused on local-scale dispersal of L. osakensis, and perhaps future studies after further establishment can monitor their dispersal over longer distances
Laricobius osakensis appears to be established at Hungry Mother State Park, Goshen, and Powhatan
Summary
The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), an insect pest native to Asia and the western United States, is causing significant mortality to eastern and Carolina hemlock trees in the eastern United States [1]. Hemlock trees are a long-lived, late successional, climax species in eastern hardwood forests, making the impact that HWA has on this tree species of critical environmental concern [2,3]. Biological control has the potential to contribute in a sustainable manner to the management of HWA and the improvement of health of hemlocks in the eastern United States. A. tsugae except the crawler stage are sedentary, and the extended amount of time spent on trees makes them accessible to predators. Beetles in the genus Laricobius Rosenhauer have been identified for biological control because they are specialists of Adelgidae [4].
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