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Consider Joining the Winsome Fly Survey: July-August!

Bill Hutchison, Suzanne Wold-Burkness, and Erin Buchholz*

*UMN Landscape Arboretum

Japanese beetle emergence – as indicated by beetles on wine grapes, or those captured in pheromone traps – is now underway in the Twin Cities metro, and perhaps other areas of southeast and southcentral Minnesota. For those who have experienced high infestation levels on farms, backyard gardens or roses, you are fully aware of the feeding damage that can occur. As part of our research on Japanese beetle (JB) population trends the past 4 years, we continue to see some good news with a biocontrol option for the pest. The Winsome Fly (WF, Istocheta aldrichi) is currently one of the most noticeable and notable JB biocontrol agents in Minnesota.


WF eggs on mating pair at vineyard, near Montreal, Quebec (credit: Jacques Lasnier.)
Usually only 1 or 2 WF eggs are laid per JB; however, when host density is low, higher egg-lay can occur.

We have now documented WF parasitism rates of 10-50%. WF has the potential to have a significant impact on JB as the time of emergence (phenology) of the fly now matches that of JB quite well, WF prefers to lay eggs on JB females which reduces the number of eggs laid by JB females, which in turn can reduce the local JB population emerging the following summer. WF is also able to maintain itself when JB densities are low. 

Although we have learned quite a bit about WF biology, we need a better understanding of the current distribution of the fly in Minnesota. We are now seeking volunteers who would like to assist us in searching for WF (via the highly distinctive white eggs laid on the JB pronotum, just behind the head). 

Please consider joining the Winsome Fly Survey Team for 2024!

With everyone working together this summer, we can efficiently gain a better understanding of the geographic scope and impact of this important biological control agent!  

For more information on how to get involved, and submit photo’s to the Winsome Fly Team, or iNaturalist, please see our FruitEdge web site at:

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