Another Painted Lady Irruption in the Upper Midwest

One month after the last Painted Lady irruption in the final days of June, another generation, perhaps even larger, suddenly emerged in central Iowa on July 29 and 30. I went out on a survey and collecting trip in Story and Boone Counties on the 30th, and found hundreds of fresh butterflies milling around and flying across Highway 17 and other local roads between Boone and Luther. There was also a large emergence between Polk City and Ankeny, with perhaps 200 along a stretch of highway between these towns. Hundreds were also observed along Interstate 80 in eastern Polk, Jasper, and Poweshiek Counties, but there were very few along I-80 farther east in Iowa and Johnson Counties, suggesting a somewhat localized irruption so far. Many of the butterflies seen along I-80 were flying north, but others were flying in various different directions.

Farmers in our area continue to have problems with "thistle caterpillars" feeding on their soybeans. While I was out monitoring yesterday, I met one grower who said that he had had to spend $30,000 this year for spraying his soybean fields for Painted Lady caterpillars. He was also disappointed to hear from me that there could be yet another generation of larvae before a final brood of butterflies emerges in early September to fly south.

This irruption began earlier in the month in the Omaha, Nebraska area, sometime between July 18 and July 23, as reported by @langabee from weekly surveys there. From those reports, I was anticipating another irruption in central Iowa, while wondering why it wasn't happening here for another week to 10 days after beginning in eastern Nebraska. Perhaps some observers in western Iowa can fill in the blanks here.

Posted by iowabiologist iowabiologist, July 31, 2019 20:01

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Even bigger eruption this week at the forest's prairie where we saw over 700 painted ladies mainly on Coneflowers. My brother lives between Huxley and Ankeny and when I was home last weekend he was complaining about the "thistle caterpillars" on his soybeans also. He had been spraying when we arrived.

Posted by langabee over 2 years ago (Flag)

Here is the Integrated Crop Management page from Iowa State University Extension about the Painted Lady life cycle and recommendations for when soybean damage by the larvae becomes high enough to warrant spraying the crop:

https://crops.extension.iastate.edu/thistle-caterpillar

Posted by iowabiologist over 2 years ago (Flag)

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