Assessment of the potential for hybridisation between Laricobius nigrinus (Coleoptera: Derodontidae) and Laricobius osakensis, predators of the hemlock woolly adelgid (Hemiptera: Adelgidae)

Abstract

In 2003, Laricobius nigrinus Fender was introduced into the eastern United States as a biological control agent of the hemlock woolly adelgid (Adelges tsugae Annand). Following its release, it was discovered that L. nigrinus was hybridising and producing viable progeny with Laricobius rubidus LeConte, a species native to eastern North America. Recently, Laricobius osakensis Montgomery and Shiyake was imported from Japan into the USA as a potential biological control agent of hemlock woolly adelgid. Hybridisation between L. nigrinus and L. rubidus led to interest in the outcome of interactions between L. osakensis and the other two Laricobius spp. The purpose of this study was to determine if L. osakensis could mate with L. nigrinus, if they could produce hybrid progeny, and whether mating interferes with reproductive output. Laricobius spp. were observed mating directly following emergence and found to be capable of producing sterile eggs in the absence of a mating event. Laboratory and confined field studies found no evidence that L. osakensis and L. nigrinus could produce hybrid progeny and the interaction between the two species did not result in a lower reproduction associated with interspecific mating attempts. Interbreeding should therefore not have an impact on biological control using these species. Fecundity experiments showed that L. osakensis produced eggs earlier in the season and at a higher rate than L. nigrinus, suggesting that L. osakensis may have the potential to be an even more successful biological control agent than L. nigrinus.

Keywords:

• hemlock woolly adelgid
• Laricobius
• hybridisation

Acknowledgements

The authors would like to thank Gina Davis, Peter Thomasson, Jacquelyne Brown, Ben Aigner, Christine Cho, Carrie Jubb, Meredith Schrader, McKinzie Mann, Linda Manden, Nick Brehm, Natalie Morris, Kara Tourje, Chandler Barton, Ryan Mays, and Tom McAvoy for their help at the Virginia Tech Insectary and Quarantine Lab, and Joanne Klein, Brenna Traver, Grace Mulholland, Jacquelyn Martin and Stephanie Vece for their help in the Molecular Lab.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by USDA Forest Service Cooperative Agreements 07-CA-11420004–161 and 11-CA-11420004–133.