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.

Japanese beetle with a distinct white dot on pronotum with added text pointing to it and reading "winsome fly eggs on Japanese beetle."

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 through 2025 are below.

Map of Minnesota with points indicating winsome fly observation as part of the midwest winsome fly survery

iNaturalist Midwest Winsome Fly Survey map from https://www.inaturalist.org/projects/midwest-winsome-fly-survey

Biocontrol expanding!

2024-25 results:
- MN:14 new counties (7 in ‘25)
- WI: 11 new counties (6 in ‘25)
- IA: 3 new counties
~95% of reports in July
10-50% parasitism rate
80% parasitism where it was original released in 1989-2002

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