Biocontrol and Hemlock Woolly Adelgid
Biological control, or biocontrol for short, is using a natural predator, parasitoid, or pathogen to manage the population of a pest. In the case of HWA, this means using predatory insects found in areas where HWA is native. The focus of our biocontrol lab is to research methods to grow healthy colonies of predatory insects and evaluate their effectiveness in managing HWA population growth. The goal is to establish multiple predator species throughout New York to maintain HWA populations below the level where they cause hemlock mortality. Insects we are currently studying are Laricobius nigrinus (Coleoptera: Derodontidae) and two species of silver fly, Leucopis argenticollis and L. piniperda (Diptera: Chamaemyiidae), from the Pacific Northwest. It is our hope that they will have a widespread impact on HWA and offer long-term survival for eastern hemlock populations without continued use of chemical controls.
Our Biocontrol Bugs
A beetle that we fondly call “Little Lari”, Laricobius nigrinus is a predator of HWA in the Pacific Northwest, where HWA is a native insect and does not kill hemlocks. This predator has been released in many locations in the eastern U.S. since 2003 and limited releases have been made in New York since 2008.
The timing of Laricobius‘s major life stages, or phenology, mirrors that of HWA in that it is most active during the winter and spring months. This is the time of year that HWA is growing rapidly, going through several rounds of molting and creating the “wool” that is so apparent on hemlock twigs. Adult Laricobius feed upon developing HWA “sistens” generation nymphs in the fall and winter. The adults will then lay their eggs amongst HWA as they are producing the eggs of the “progrediens” generation. The hatching Laricobius larvae will then feed on those eggs and early instar nymphs before dropping to the ground to pupate in the soil.
L. nigrinus is one of the most abundant predators in the Pacific Northwest where researchers feel natural enemies are the reason HWA populations are kept in check. It is our hope to mimic that success here in New York’s forests.
The silver flies Leucopis argenticollis and L. piniperda are another biocontrol option being researched for HWA control. Leucopis spp. are likely the most abundant predator of HWA in the Pacific Northwest but are difficult to work with. Silver fly larvae feed on of both the HWA progrediens and sistens generations, adding to the impact of Laricobius. In spring 2017, silver flies were released at 10 sites in New York and preliminary survey has found them to have established at all sites.
Silverflies are released in the spring. Releases involve placing a bug bag over an infested hemlock branch so that flies stay on that branch to mate and lay eggs. Once the larvae hatch and begin to feed, we can assess the success of release by returning to monitor their progress.
Our Biocontrol Program
Since 2003, Laricobius beetles have been released in 16 states and have had successful establishment at most release sites. First released in New York in 2008, Laricobius has been confirmed established at three sites in the state and we are hopeful that further research and releases will continue to prove successful going forward. Located at Cornell University, the New York State Hemlock Initiative biocontrol research lab will join the ranks of biocontrol labs in North Carolina, Tennessee, Georgia, and New Jersey in the efforts to control HWA on the East Coast.
One challenge in growing colonies of live insects in the lab is the availability of food. Since the predators rely on populations of HWA for food, it is imperative that we can provide for them continually in the lab. Field collection of heavily infested hemlock branches from throughout New York is the only option we have to do this. It is critical that we have help locating heavy HWA populations to keep the lab supplied. We are also searching for trimmed hemlock hedges across the state to act as “field insectaries”. When hedges become infested with HWA we hope to release predators so they can grow their populations and be easily collected and redistributed to forested sites with HWA. Landowners with hemlock hedges are particularly important in this effort. If you are interested in hosting a field insectary for HWA predators, you can find more information here.