It is important to note that several beetle species have been evaluated and tested as biological controls by the USDA and others; and they do not all perform the same. They all have their pros and cons and their performance is still being assessed. None are likely to act as a stand-alone silver bullet; though, they are considered to be an essential component of long-term hemlock woolly adelgid (HWA) control. An overview of several species that have been evaluated can be found here.
The species that has so far shown the most promise as a biological control agent is Laricobius nigrinus, a predator beetle native to the Pacific Northwest. It has been found in close association with HWA on western hemlock, Tsuga heterophylla, in the Pacific Northwest, where HWA is not considered a forestry pest. L. nigrinus is active from October to March; both adults and larvae will consume all stages of HWA: eggs, nymphs and adults.
After exhaustive evaluation in quarantine labs, it was cleared by the USDA for use as an HWA bio-control in the eastern United States in 2000 and has been released in NC since 2003. As of 2009, field-caught and/or lab-reared L. nigrinus have been released in 15 eastern states. Additionally, a potentially more cold-hardy strain of L. nigrinus from Idaho has been released in northeastern states where low winter temperatures may challenge the pacific strain.
Laricobius is a genus of beetles in the family Derodontidae, the tooth-necked fungus beetles. There are three species native to North America: L. nigrinus and L. laticollis are native to western North America, and L. rubidus is native to eastern North America. All members of the genus Laricobius are only known to prey on adelgids. The other three genera in this family of four genera feed on fungi or the by-products of fungal metabolism. This family is not commonly encountered in the field, possibly due to its small size (< 3 mm).
Scientists first discovered hemlock woolly adelgids in Great Smoky Mountains National Park in 2002. Since then, the park has “created the most ambitious program in the Southeast aimed at protecting hemlocks.” Learn about their bio-control efforts here.
The long-term goal of implementing biological control is to reduce our dependence on chemicals by establishing a predator-prey relationship that keeps the adelgid population at a level hemlocks can tolerate.
However, this method of HWA-control is not currently appropriate for every situation. Beetles placed on an individual tree, no matter the number or species, may choose to fly to a different location and therefore cannot be guaranteed to “save your trees.” Furthermore, the effectiveness of predator beetles to reduce adelgid populations varies with the species of beetle and other factors and is still under evaluation. It is a landscape level approach, which will hopefully eventually benefit everyone who has a hemlock on their property. But this will take time and patience. In the meantime, individual landowners most reliable and affordable option is to continue to chemically treat their hemlocks while we wait for the bio-control program to mature.
Learn about the “Beetles Save Needles” program and community trainings hosted by the Blue Ridge Resource Conservation and Development Council, an HRI partner and award recipient, here. The agenda and speaker list for the NC HWA Bio-control Forum, held in Montreat, NC on February 24-25, 2016 can be found here. Please contact firstname.lastname@example.org for videos of the presentations.
In the May 2015 meeting, the Buncombe County Board of Commissioners unanimously approved the purchase of 5,000 Laricobius nigrinus beetles to be released on remaining high quality hemlock stands on public and municipally held lands that provide benefit to the county as a whole. Follow the county’s hemlock preservation project here.
MORE INFORMATION COMING SOON…