Winsome Fly Survey

Winsome fly & Japanese beetles

Winsome fly, Istocheta aldrichi, is a biocontrol for Japanese beetles. Winsome fly (WF) was first introduced in 1922 and has been noticeable in Minnesota since 2017. During the past 3 summers, WF parasitism rates have been increasing (range, 10-60%) in several Metro areas.

To help better understand the distribution and density of this biocontrol agent, report Winsome fly observation to iNaturalist. Also confirm your interest in by emailing: hutch002@umn.edu. Researchers from Bill Hutchison's UMN Entomology lab will be in touch.

Visit the UMN Extension website if you need help identifying Japanese beetles.

Photo by Whitney Cranshaw, Colorado State University, Bugwood.org, text added by A. Gupta

Using iNaturalist

Watch this 1:24 minute video to learn how to report to iNaturalist.

Good pictures matter

Parasite identification can be tricky so good photos are critical. This project is focused on observations of WF eggs, which are laid near the head of Japanese beetles, making them easy to see. For each iNaturalist report, provide at least 2-3 good images of the WF egg(s) on a Japanese beetle from several angles. Make sure the WF egg is visible and the photo clear.

All questions about this project should be directed to hutch002@umn.edu. Visit the Extension Winsome fly webpage for more information.

This is a multi-year project. Results from 2024 are below.

In Minnesota there was an increase in known winsome fly reports from 9 known counties to 21 (north to Carleton Co; south to Fillmore Co.; and west to McLeod Co.) and in Wisconsin there was an increase from 4 counties to 10 counties, showing an eastward radiation out from Twin Cities as far north as Oneida Co. Given the known release dates in 1998 and 2002 the data for Oneida County resulted in a slightly faster spread rate of impacted Japanese beetles. Current data suggests a spread rate of 14-16.5 kilometers per year, rather than the previously recorded 12 kilometers per year previously published for the beetle.

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