Slinging more Silver flies this spring...

We have been at it again this spring with a new predator of hemlock woolly adelgid (HWA).  This is our third consecutive year releasing silver flies on HWA infested hemlocks.

A hemlock branch with both the fall (sistens) and spring (progrediens) generations of HWA.

You see, one of the more annoying characteristics of HWA is that they can produce two generations of offspring in one year.  A fall, sistens generation and the spring, progrediens generation.  The predator beetles that we are so fond of are only active during the fall, which means the adelgids have an entire season to feed and reproduce without the presence of a predator. 

Well, we aim to end that with the introduction of silver flies! 

Our work thus far is with two different Leucopis spp., argenticollis and piniperda.  Both of these species are native to North America.  The silver flies in the West, where hemlock woolly adelgid have been active for millenia, live on hemlocks and feed on HWA.  The silver flies in the East, where HWA has only been resident for the last 50 some odd years, do not live on hemlocks or feed on HWA. So, we are introducing a Western biotype of a native species in order to eat an exotic invasive pest.

I will spare you the lengthy details on permitting and logistics of such an experiment.  Just know that this involves a whole lot of people at several state and federal agencies making sure all that we do is upright and in-line.  We have an amazing cooperator in the Pacific Northwest rearing flies and sending them to us for our experiment.  The big idea in all of this is to establish biological control agents that are able to eat, harass, harangue, or otherwise subjugate HWA, so our hemlock trees can live long happy lives with only minimal damage from the pesky adelgid.

University of Vermont graduate student Kyle Motley readies branches to receive silver flies.

This years experiment is the largest yet with field sites from South Carolina to New York including Great Smoky Mountains National Park in Tennessee.  We are hoping for more positive results!

 A sleeve cage is mounted on an infested hemlock branch. 

We are releasing flies into sleeve cages on infested branches at our field sites, then returning at predetermined intervals to collect the samples in order to find out how well flies are feeding and reproducing. 


"Now here we go dropping science, dropping it all over..."
-Beastie Boys from "The Sounds of Science"