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You are here: NRS Home / Research Programs / Forest Disturbance Processes / Invasive Species / Hemlock Woolly Adelgid / Control and Management /Biological Control / Silver fly Predators of the Hemlock Woolly Adelgid in the Pacific Northwest
Hemlock Woolly Adelgid

Silver fly Predators of the Hemlock Woolly Adelgid in the Pacific Northwest

Research Issue

[photo:] Leucopis argenticollisPredatory silver flies (Diptera: Chamaemyiidae) are among the most important natural enemies regulating adelgid species in their native ranges. For the hemlock woolly adelgid (HWA), two species from western North America, Leucopis argenticollis and L. piniperda, show promise as biological control agents.

The family Chamaemyiidae includes two subfamilies, about 20 genera and subgenera, and an estimated 100-150 species worldwide. The adults are small, stocky flies (1-4 mm), silvery gray to brown, but occasionally shiny black.  Larvae are predators of adelgids, aphids, coccids, and scales.  As a result, they have been considered as biological control agents of pest insects in those groups.  In predator surveys of hemlock woolly adelgid (HWA) populations in Oregon and Washington, silver flies were abundant; second only to the derodontid beetle, Laricobius nigrinus Fender.  Given the widespread occurrence and abundance of silver flies in the Pacific Northwest, they is being studied to understand their role in the population dynamics of HWA in the West as well as their potential as a biological control agents in the East.

Our Research

The goal of this project is to learn more about the potential of western silver flies for HWA biological control.  We are using morphological and DNA sequence data to determine phylogenetic relationships within the family Chamaemyiidae to see where these species fit in. This will also allow us to identify variation within and among the western species that feed on HWA. In addition, we are developing a DNA Barcode database for identifying immature life stages that cannot currently be identified to species with morphological characters. This will aid in determining impact of the flies in their current ranges as well as monitoring their establishment and spread following their release as biological controls.

Other objectives include:

  • Determine the phenology of silver flies in the Pacific Northwest.
  • Develop laboratory rearing methods for western silver flies.
  • Evaluate the suitability of alternative prey for western silver flies.
  • Test whether western silver flies will feed and develop on HWA from the eastern U.S.
  • Determine the impact of western silver fly predation on HWA populations in bagged field studies.
  • Begin releases of western silver flies in the eastern U.S. to determine the most effective release strategies

Expected Outcomes

This project will provide definitive data on the suitability of western silver flies for HWA biological control.

Research Results

These same two silver fly species found on HWA in the Pacific Northwest are also reported in the East, where neither has been collected from HWA – only from other native and non-native adelgid species.  We found that the specimens of L. piniperda collected from pine adelgids in Connecticut, Maryland, Virginia, and West Virginia are genetically separate from those collected from western HWA in Washington and Oregon. Similarly, L. argenticollis collected from pine adelgids in Minnesota and Pennsylvania are genetically distinct from specimens collected on western hemlock woolly adelgid in Washington, Oregon, and Idaho. It appears that for both species, there may be different populations that specialize on different adelgid prey species in the West versus East - i.e. western flies prefer hemlock woolly adelgid and eastern flies prefer pine adelgids.

The phenology of western silver flies and HWA are closely synchronized in the Pacific Northwest.  Western silver fly larvae are most abundant during the egg stages of the two annual HWA generations, and there is a strong positive correlation between silver fly abundance and adelgid population density. Western silver fly larvae sent to the Forest Service lab in Hamden did feed and develop on eastern HWA. 

Overall results of the host specificity tests demonstrate that Leucopis spp. collected from HWA infested western hemlock show a slight preference for HWA over balsam woolly adelgid, Cooley spruce adelgid, and pine bark adelgid, although they will feed on all four species of adelgids.

Publications

Kohler, G.R.; Stiefel, V.L.; Wallin, K.F.; Ross, D.W. 2008. Predators associated with the hemlock woolly adelgid (Hemiptera: Adelgidae) in the Pacific Northwest. Environmental Entomology 37: 494-504.

Kohler, G.R.; Stiefel, V.L.; Wallin, K.F.; Ross, D.W. 2008. Parasitoids reared from predators of hemlock woolly adelgid (Hemiptera: Adelgidae) and the hymenopterous parasitoid community on western hemlock in the Pacific Northwest. Environmental Entomology 37: 1477-1487.

Research Participants

Principal Investigators

  • Nathan Havill, Research Entomologist, U.S. Forest Service, Northern Research Station
  • Adalgisa Caccone, Yale University, Department of Ecology and Evolutionary Biology
  • Darrell Ross, Professor, Oregon State University, Department of Ecosystems and Society, Corvalis, OR
  • Kimberly Wallin, University of Vermont and U.S. Forest Service, Northern Research Station, Burlington VT
  • Stephen Gaimari, California Department of Food and Agriculture

Research Partners

  • Albert (Bud) Mayfield, Research Entomologist, U.S. Forest Service, Southern Research Station, Asheville, NC
  • Mark Whitmore, Extension Associate, Cornell University, Ithaca, NY

Last Modified: 05/08/2015