Seasonal Assessment of Supercooling Points for Two Introduced and One Native Laricobius spp. (Coleoptera: Derodontidae), Predators of Adelgidae

The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive insect that threatens hemlock species in eastern North America. Several species from the genus Laricobius are predators of A. tsugae in its native areas of Asia and the western United States. Two Laricobius species have been released as biological control agents: Laricobius nigrinus Fender, and Laricobius osakensis Montgomery and Shiyake. Laricobius rubidus LeConte is an adelgid predator native to the Eastern United States, where it can feed and complete development on A. tsugae opportunistically. Laboratory assays were conducted to assess the cold hardiness of these three Laricobius species, including two distinct populations of L. osakensis, by measuring the supercooling points of each species from November 2016 through March 2017. This information may be useful for choosing the best-suited biological control agent for a particular region to control A. tsugae. There was a significant difference between the overall mean supercooling point of L. rubidus compared to the other Laricobius spp. There were also significant differences of supercooling points between L. rubidus and both strains of L. osakensis in January, and significant differences between L. rubidus and all other strains in February. L. rubidus appear better adapted to cold extremes in the eastern U.S. than imported Laricobius spp.

Coexistence of three specialist predators of the hemlock woolly adelgid in the Pacific Northwest USA

The hemlock woolly adelgid (Hemiptera: Adelgidae: Adelges tsugae Annand) is an invasive insect, introduced from Japan to eastern North America, where it causes decline and death of hemlock trees. There is a closely related lineage of A. tsugae native to western North America. To inform classical biological control of A. tsugae in the eastern USA, the density and phenology of three native western adelgid specialist predators, Leucopis argenticollis (Zetterstedt), Le. piniperda (Malloch) (Diptera: Chamaemyiidae), and Laricobius nigrinus Fender (Coleoptera: Derodontidae), were quantified in the Pacific Northwest. Infested branches were collected from western hemlock (Pinaceae: Tsuga heterophylla (Raf.) Sarg.) at four sites around the Puget Sound, Washington and three sites in Oregon. Immature Leucopis were identified to species using DNA barcodes. Leucopis argenticollis was roughly twice as abundant as Le. piniperda. Laricobius nigrinus larvae were more abundant than the two species of Leucopis during the egg stage of the first adelgid generation, but Leucopis were present as feeding larvae during the second adelgid generation when La. nigrinus was aestivating in the soil, resulting in Leucopis being more abundant than La. nigrinus across the entire sampling period. Adelges tsugae and La. nigrinus densities were not correlated, while A. tsugae and Leucopis spp. densities were positively correlated. Leucopis spp. and La. nigrinus densities were negatively correlated. These results support the complementary use of La. nigrinus and the two Leucopis species for biological control of A. tsugae in the eastern USA, and point to the need for further investigation of spatial and temporal niche partitioning among the three predator species.

Establishment and Distribution of Laricobius spp. (Coleoptera: Derodontidae), a Predator of Hemlock Woolly Adelgid, Within the Urban Environment in Two Localities in Southwest Virginia

Hemlock woolly adelgid (HWA), Adelges tsugae Annand, is a highly destructive non-native pest lethal to eastern hemlock, Tsuga canadensis (L.) Carrière, and Carolina hemlock, T. caroliniana Engelmann. Fifty years following the first observation of HWA in eastern North America, a predatory beetle, Laricobius nigrinus Fender, was evaluated, approved, and released as a biological control agent. Efforts were made to mass rear L. nigrinus with the goal of redistributing the beetles on public lands, typically in forest ecosystems, as a secondary option to silvicultural and chemical controls. The majority of L. nigrinus releases has occurred on public lands. Herein, we report the observation of L. nigrinus within the urban environment outside of known release locations. Two towns, Blacksburg and Radford, were divided into 0.40 km2 grids. A total of 27 and 19 grids were randomly selected from each town, respectively. Hemlocks were present in 44 and 42% of the grids surveyed in Blacksburg and Radford, respectively. In Blacksburg and Radford, 86 and 100% of the grids with hemlocks were infested with HWA, and of those infested hemlocks, Laricobius spp. was present in 100 and 75% of grids, respectively. A total of 154 Laricobius spp. (98% L. nigrinus and 2% Laricobius rubidus) adults were collected between each town. While it is unclear the level of control L. nigrinus has on reducing HWA's impact, the establishment of this biological control agent in the urban environment is an additional level of predation, that would otherwise not be present, for homeowners with HWA-infested trees.

Seasonal phenology and abundance of Leucopis argenticollis, Leucopis piniperda (Diptera: Chamaemyiidae), Laricobius nigrinus (Coleoptera: Deridontidae) and Adelges tsugae (Hemiptera: Adelgidae) in the Pacific Northwest USA

Adelges tsugae infested western hemlock trees were sampled periodically for 1 year at two locations in Oregon and Washington to compare the phenology and abundance of three associated predators (Leucopis argenticollis, Leucopis piniperda, and Laricobius nigrinus) and their host. On each sample date, two 3–10 cm long terminal twigs were collected from each tree and brought to the laboratory to count all life stages of A. tsugae and the three predators. Peak larval abundance of Leucopis spp. and La. nigrinus coincided with the presence of A. tsugae adults and eggs. Leucopis spp. larvae were present for a much longer period of time than were La. nigrinus larvae. Furthermore, Leucopis spp. larvae were present during both the progrediens and sistens egg stages, while La. nigrinus larvae were only present during the progrediens egg stage. Overall, we collected 2.3–3.5 times more Leucopis spp. of all life stages than La. nigrinus. These results support the continued study of Leucopis spp. from the Pacific Northwest as biological control agents for A. tsugae in the Eastern USA.