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 [https://www.inaturalist.org/people/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.
-- Royce Bitzer, July 31, 2019