Finding the first Japanese beetle each June is a point of pride for some, including folks in my lab. They found adults in corn this week. Hurrah!? Checking the accumulating degree days for 2025 confirms they should be emerging all throughout Iowa. They need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days.
These insects usually stand out in a crowd of other scarab beetles (e.g., May beetles, chafers, June beetles, etc.). Japanese beetles are iridescent with a metallic green head and thorax with copper-colored forewings. There are five tufts of white hairs on each side of the abdomen.
Find out more:
Biology and management of Japanese beetle in corn and soybean: https://academic.oup.com/jipm/article/10/1/9/5454734?login=true
Soybean Insect Defoliation Training Tool: https://crops.extension.iastate.edu/encyclopedia/japanese-beetle-corn-and-soybean
Managing Japanese beetles in yards and gardens: https://yardandgarden.extension.iastate.edu/encyclopedia/japanese-beetle
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- Extension Entomologist Specialist
- ANR Crops Team Leader