Laricobius nigrinusFender, native to the Pacific Northwest, is being evaluated as a potential biological control agent of the hemlock woolly adelgid,Adelges tsugaeAnnand, in the eastern United States. Members of the genusLaricobiusfeed exclusively on adelgids.Adelges tsugaeis found on hemlocks (Tsugasp.) in North America and Asia, but is considered only a pest of eastern [Tsuga canadensis(L.) Carrière] and Carolina (Tsuga carolinianaEngelmann) hemlocks in eastern North America. This is the first detailed study of the life history ofL. nigrinusand its interaction withA. tsugae. Results of a 2-year field study conducted in a seed orchard in British Columbia on the seasonal abundance ofL. nigrinusand its prey,A. tsugae, revealed that (i) the sistens generation ofA. tsugaematures 2-3 months earlier than previously reported in Virginia and Connecticut, (ii) noA. tsugaesexuparae were observed, which differs from findings in Virginia and Connecticut, (iii)L. nigrinusadults undergo an aestival diapause that coincides with diapausing first instarA. tsugaesistens, and (iv) oviposition and subsequent larval development ofL. nigrinuscoincides with oviposition by theA. tsugaesistens adults, indicating good synchrony betweenL. nigrinusand suitable prey stages ofA. tsugae.

Eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana) of eastern North America have been attacked by the non-native hemlock woolly adelgid (Adelges tsugae Annand) (HWA) since the first half of the 20th century. Unlike most insects, HWA develops through one generation from fall to late winter, exposing this insect to the lethal effects of winter temperatures. The mortality inflicted by winter temperatures on HWA determines the surviving population density as well as its ability to spread to uninfested areas. With the ongoing changes in climate, knowledge of this species’ ability to survive and spread in the future can help land managers prepare for its management. This study began during the winter of 2014 and ended in the spring of 2017. During this period, winter mortality of HWA was recorded at 100 sites from Maine to Georgia (n = 209). Changes in population density from the sistens to the succeeding progrediens generation were recorded at 24 sites (n = 35). Models were developed to predict HWA mortality using the lowest minimum temperature prior to the mortality assessment date, the number of days with mean temperature <−1 °C, and the mean daily temperature of the three days preceding that minimum. Models were also developed to predict population density changes from the overwintering sistens generation to the following progrediens generation. Future projections under climate change showed increases in winter survival and population growth rates over time. Especially towards the northeastern edge of T. canadensis’ distribution as minimum temperatures are predicted to increase at a greater rate. This will result in an increase in density throughout its current distribution and expansion northward causing an increase in its impact on eastern Tsuga spp.

Two hemlock woolly adelgid, Adelges tsugae Annand, generations complete their development on hemlocks (Tsuga spp.) that are native to eastern North A

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.

There are three generations of hemlock woolly adelgid, Adelges tsugae Annand, that develop on the secondary host Tsuga spp. Two of these generations, the progrediens and sexupara, are present concurrently in the spring. Sistens are present from early summer until the following spring. Constant temperature studies were conducted to quantify the influence of temperature on hemlock woolly adelgid progrediens development and to develop a degree-day model. Progrediens development in the field also was sampled to test the accuracy of the model. Hemlock woolly adelgid progrediens developed at temperatures ranging from 4 to 22°C. Duration of first-instar progrediens was less dependent on temperature than in the other nymphal stages and may have been a result of the difficulty in determining the median point of settled first-instar nymphs and the inability to distinguish progrediens from sexuparae at this stage. Duration of development from second stadium to adult was highly dependent on temperature. Using this range of progrediens stages, it was determined that the low temperature threshold was 3.9°C and requires 222 degree-days to reach the adult stage. The number of degree-days needed to complete development in the field ranged from 110 to 123% of degree-days required to complete development in the laboratory.