Optimizing integrated pest management (IPM) for plum curculio in Illinois peaches

Plum curculio (PC), Conotrachelus nenuphar (Herbst.) (Coleoptera: Curculionidae), is an important pest of peaches and apples. It is an internal fruit feeder, so growers can only control it during the window between adult emergence and egg laying. Control failures could be due to insecticide resistance or a mismatch of plum curculio life cycles and spray timings. The number of plum curculio generations per year varies by region and most of the peach growing regions in Illinois were thought to have one generation of plum curculio. Substantial control failure in 2022 led to this project with three objectives. (1) Develop effective monitoring techniques for adult PCs, (2) identify the number of PC generations in the major peach growing regions of Illinois, and (3) investigate insecticide resistance in Illinois PC populations. In 2023, we placed trunk traps baited with benzaldehyde lures on commercial peach trees. The traps intercepted plum curculios early in the season, but none in mid-summer. Contrary to trap catch, first and second instar plum curculio larvae were inside fruit in mid-summer indicative of a second generation. Additionally, our laboratory reared plum curculio larvae successfully emerged as adults in mid-summer, further suggesting that we have bivoltine plum curculio. In 2024, we compared Methyl salicylate with Grandiosic acid lures to successfully intercept the second-generation adults. Additionally, we investigated insecticide resistance in 2024 using laboratory bioassays and molecular assays. Overall, this study seeks to optimize effective IPM program for plum curculio and eliminate extraneous insecticide sprays.