Spring is in the air, and soon our silver flies will be as well. This time of year, as our Laricobius beetle larvae are moving into their pupation phase, we receive Leucopis silver flies on HWA-infested foliage from the Pacific Northwest. This year we will be releasing silver flies and, like last year, researching silver fly rearing techniques in the lab.
Currently, we rely on our spring collecting trips to the Pacific Northwest to provide all of our silver flies for releases. While this system does provide us with enough flies for several releases each spring season, it also means that the number of flies we are able to release here in New York is dependent upon the number of flies that come from our northwest collecting sites. In the Pacific Northwest, where HWA is native, the density of predator species like silver flies depends on the amount of food–HWA–there is available. Ample HWA populations result in high densities of predators, while low HWA populations mean predators are scarce and we are unable to collect high numbers of flies for release. Currently the number of flies we can release is inconsistent year to year, based on the number of flies we can find and ship back to the lab. However, our research team is hard at work to find solutions to this problem.
This year we are continuing to improve techniques for rearing flies in the lab. If we are successful, we will not need to be so dependent on the numbers of flies we find in the Pacific Northwest for our releases each year. This will enable us to improve our biocontrol program and our ability to manage HWA populations on the East Coast in the long term. This process is challenging. Silver fly larvae eat HWA eggs in order to survive and develop into adult flies, and so we need to have a steady supply of HWA eggs throughout the year to provide in order to rear a fly colony in the lab. There are two ways to tackle this challenge: one way is to artificially lengthen the egg-laying window of HWA so that there are eggs present for a longer amount of time each season, and the other way is to force a diapause, or a period of suspended development, in the flies to buy time until HWA eggs are available. By experimenting with some of the flies we collect each spring, we can hone our methods for fly rearing.
Last year, we were able to rear silver flies in the lab to the second generation. This year we are hoping for even greater success. As the snow melts and the HWA begin laying eggs, we are gearing up for an exciting spring season both in the lab and in the field. There is always more to learn, and we look forward to sharing the results with you soon.