Dave Shetlar (OSU Entomology, Professor Emeritus) and I had a conversation early last week about what had become of Japanese beetles (Popillia japonica) this season. Neither of us had yet seen our first adults in central and southwestern Ohio, respectively.
Normally, beetle emergence is well underway by around mid-June in central and southern Ohio. We wondered whether or not heavy spring rains had drowned the pupae which are unable to flee flooded pupal chambers.
I finally saw my first beetles yesterday in southwest Ohio, although I only found 10 after walking about a mile on a trail next to a fence line dominated by wild grape (a.k.a. Japanese beetle candy). When I phoned Dave, he reported that he had found beetles this past Friday; however, he had likewise observed low numbers.
On the other hand, Curtis Young (Van Wert County) reported on Tuesday during our BYGL Zoom Inservice that he was finding respectable numbers of adults in northwest Ohio. That part of the state experienced some of the heaviest rainfall and continuously wet conditions this spring which threw water on the drowned pupae theory.
The bottom line is that it's probably too early to make any predictions regarding the overall outlook for this year's Japanese beetle populations in any part of the state as well as the resulting white grubs. We experienced some high localized Japanese beetle populations last season, particularly in the central and southern parts of the state. Perhaps adult emergence is simply running late this season and we will see increasing numbers. Only time will tell.