Evaluation of laricobius nigrinus (coleoptera: derodontidae) oviposition behavior and the efficacy of egg-stage releases as a biological control method of hemlock woolly adelgid (adelges tsugae; hemiptera: adelgidae) in Western North Carolina

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Lauren Michelle Gonzalez (Creator)
Western Carolina University (WCU )
Web Site: http://library.wcu.edu/
James Costa

Abstract: The hemlock woolly adelgid (HWA), Adelges tsugae (Hemiptera: Adelgidae), is an invasive and devastating pest of native hemlock trees in eastern North America. Since HWA’s introduction to western North Carolina in the early 2000s, state and federal agencies have been attempting to preserve eastern and Carolina hemlock in the region through both chemical treatments and biological control. Chemical control in a forest ecosystem is not as viable an option due to high costs and environmental impacts, making biological control using natural enemies an important management goal. Currently, the most commonly released predatory beetle to combat HWA in eastern North America is Laricobius nigrinus (Coleoptera: Derodontidae). However, laboratory rearing of L. nigrinus has been constrained by high mortality rates (65-75%). This mortality rate can be partially explained by the life cycle of L. nigrinus, which in nature pupates in the soil and undergoes a dormant period during the summer similar to HWA. The struggle with low emergence rates may suggest that the beetles may be especially sensitive to environmental factors during their pupation period. It is important that adult predator beetles emerge as HWA is emerging in the field, otherwise early emergence can result in high mortality due to lack of available food. To try and overcome these low lab-reared survival rates and reduce the risk of unsynchronized emergences, the efficacy of releasing lab-oviposited L. nigrinus eggs in the field instead of lab-reared adults was evaluated. In addition, the oviposition rate of L. nigrinus was tested based on different female beetle densities to help develop an efficient lab oviposition protocol. Trends suggested a negative density-dependent relationship indicating that the number of mated females should be limited per oviposition cage to ensure the highest number of eggs laid. In the fall and winter of 2020-2021, a recovery experiment was conducted using soil emergence tents in Jackson County, North Carolina, by releasing approximately 230 L. nigrinus eggs. The soil emergence tents recovered five times as many adult L. nigrinus underneath trees where L. nigrinus eggs were released when compared to control trees that had no egg releases, providing strong evidence that this deployment method is valid. Together these studies suggest that altering current oviposition protocols and releasing L. nigrinus in the egg stage rather than as adults could be less labor intensive and a more cost-effective approach to HWA biological control – qualities needed in the struggle to manage HWA populations. Finally, recommendations for new protocols are provided for lab managers and forest health professionals that rear and release L. nigrinus populations.

Additional Information

Language: English
Date: 2021
Tooth-necked fungus beetles
Biological pest control agents
Hemlock woolly adelgid
Carolina hemlock

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