Laricobius nigrinus (Coleptera: Derodontidae) is a beetles species native to the Pacific Northwest, where HWA is a native pest of western hemlock and mountain hemlock trees. The family Derodontidae is mainly a family of fungus-feeding beetles, with the exception of the genus Laricobius, which only feed on adelgids. L. nigrinus is a specialist predator that feeds exclusively on developing and adult HWA throughout the fall and winter seasons while HWA are in their first of two annual generations. Our lab rears Laricobius beetles from their spring pupal stage, through their larval stage, and releases beetles as adults in the fall. The New York State Hemlock Initiative has released Laricobius at 21 sites across New York since 2008.
Laricobius Rearing Program
When our biocontrol lab officially opened in 2017, we sought to establish a Laricobius rearing program with two beetle species. In 2017 and 2018, we reared L. nigrinus, as well as Larcobius osakensis, another HWA predator native to Japan, in our main lab space. In 2019, we continued to work with these beetle colonies and collected an additional group of L. nigrinus beetle prepupae from Pacific Northwest foliage obtained during our spring collections, which we reared to adulthood in a quarantine facility. The L. nigrinus reared from their prepupal stage had the highest adult emergence following pupation, and had life-cycles that were better aligned with HWA aestivation break in the fall season than our other two lab-reared colonies. Based on these results, we continue to systematically collect beetle prepupae from spring-collected western hemlock foliage to support our fall beetle releases going forward.
Laricobius Starvation Experiment
In 2019, we investigated the effects of food-limitation on developing Laricobius beetles. This experiment aimed to replicate the effects of HWA mortality on Laricobius food availability during winter months, when HWA populations crash a result of cold temperatures. We expected that limiting food would have a negative impact on beetle ovary development, which would slow beetle population growth and spread. While the results from this study were not statistically significant due to the small sample size, we have a better understanding of limits to Laricobius populations growth in New York. Beetle reproduction is a crucial part of biocontrol management success, so this study has given us new insights to improve our program going forward.
In 2018 and 2019, we used two sampling methods to confirm beetle establishment: beat-sheeting to find adult beetles on hemlock branches, and larval sampling for a more fine-grained approach. So far, we have been able to confirm beetle establishment at five of our twenty-one release sites. In 2019, we found establishment at four of the sites where beetles were originally released in 2009, confirming the tenth generation of beetles in New York. While these initial results are promising, we are currently working to develop methods for more efficient predator sampling.
Searching for tiny Laricobius beetles to confirm establishment in the field is akin to searching for needles in a very big haystack, but is absolutely critical to determine establishment and spread. With that in mind, we are always looking to develop more efficient sampling techniques that will allow us to find HWA predator populations in the field. In late 2019, we began to investigate the use of environmental DNA, or eDNA, to detect the presence of HWA predators. We are currently refining eDNA sample collection methods with the intention of deploying passive samplers in the field in 2020.
Getting Involved with Laricobius Projects
Our lab needs to know about HWA dynamics in New York and where to release predators to make the biggest impact. We look specifically for areas with relatively healthy hemlock trees and dense HWA populations for ideal release sites. The best way to help us find biocontrol release sites is by joining our HWA Hunters survey team:
Other Ways to Contribute
Collect HWA Phenology Field Data
In order to accurately time our biocontrol releases, we rely on citizen scientists around the state to monitor local HWA populations for transitions between major life stages. For Laricobius beetles, this means watching for HWA to wake from its summer dormant period and begin feeding. You can learn more about the timing of HWA’s major life cycles and why it is so critical for our biocontrol program on our HWA Phenology page.
Host a Hemlock Hedge Insectary
If you have a hemlock hedge, you can help us by making your hedge a biocontrol bug insectary. Hemlock hedges help us to raise a small population of Laricobius beetles adapted to the local climate for nearby releases. To learn more about our hemlock hedge program, you can visit our Hemlock Hedge page.