A predator case history: Laricobius nigrinus, a derodontid beetle introduced against the hemlock woolly adelgid.
The hemlock woolly adelgid, Adelges tsugae (Homoptera: Adelgidae) is an invasive alien pest of eastern North American hemlocks (Tsuga spp.) and is the target of a classical biological control programme in the eastern USA. Host range testing conducted under quarantine in Blacksburg, Virginia determined the suitability of Laricobius nigrinus (Coleoptera: Derodontidae) a predatory beetle, as a biological control agent of this pest. Members of the genus Laricobius are known to feed on adelgids. L. nigrinus, native to western North America, was tested on 3 other adelgid and 3 non-adelgid species of Homoptera in 3 families. Host acceptance and host suitability tests were conducted on test prey. In paired-choice and no-choice oviposition tests, L. nigrinus females preferred to oviposit in HWA ovisacs over the other test species. Feeding tests showed that L. nigrinus consumed more ova of HWA than ova of Adelges piceae [Dreyfusia piceae] and Pineus strobi, but not of Adelges abietis. In larval development tests, L. nigrinus only completed development on HWA. These results suggest that L. nigrinus has a narrow host range and that it has potential for biological control of HWA. L. nigrinus was cleared for field release by USDA APHIS in 2000 based on these findings and NAPPO Guidelines for 'Petition for Release of Exotic Entomophagous Agents for the Biological Control of Pests'. Test design will be discussed in a retrospective analysis in relation to the practical realities of host range testing in this system and compared with what might be the ideal.