Abstract
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.
Highlights
The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest in the native range of eastern hemlock, Tsuga canadensis (L.) Carriere, and Carolina hemlock, Tsuga caroliniana Engelmann, and has caused considerable hemlock mortality across a large portion of easternNorth America [1,2,3]
L. rubidus appear better adapted to cold extremes in the eastern U.S than imported Laricobius spp
The beetles from that study were kept in mesh cages on hemlock trees in Leverett, MA for four weeks before the supercooling lab work was conducted [22]. These supercooling points are lower than what we found in our study, which was −14.1 ◦ C (±0.9) for L. nigrinus in January
Summary
The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest in the native range of eastern hemlock, Tsuga canadensis (L.) Carriere, and Carolina hemlock, Tsuga caroliniana Engelmann, and has caused considerable hemlock mortality across a large portion of easternNorth America [1,2,3]. The density of the biological control agent HWA, Laricobius osakensis Montgomery, and Shiyake (Coleoptera: Derodontidae) decreased concurrently with its host, HWA [7] This event came two years after the initial releases of this insect, making it difficult to determine if their lack of establishment was due directly to the extreme temperatures or indirectly due to loss of prey. The populations of another biological control agent native to the western United States, Laricobius nigrinus Fender were negatively impacted by the effects of the polar vortex [8,9]. Laricobius rubidus is a native specialist predator of the pine bark adelgid (PBA), Pineus strobi (Hartig) (Hemiptera: Adelgidae) [10,11,12,13]
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