Annual and Seasonal Changes in Parasitism Rates by Hadronotus Pennsylvanicus (Hymenoptera: Scelionidae) on the Squash Bug Anasa Tristis (Hemiptera: Coreidae) in Squash Fields: Implications for Augmentative Releases

SIMPLE SUMMARY: The squash bug is a serious insect pest of squash and other cucurbit crops in North America. Squash bugs damage the crop by feeding on plant leaves, stems, and fruits, leading to significant reductions in fruit yield with economic losses for growers. While use of insecticides helps lower squash bug numbers, it can have negative effects on the environment and on important beneficial insect species like pollinators and other beneficial insects. Alternatives such as biological control are not well studied for squash bugs. The squash bug has an important natural enemy, the native parasitoid wasp Hadronotus pennsylvanicus, which attacks the squash bugs’ eggs. From 2016 through 2021 in Maryland, we monitored parasitism of squash bug eggs through the season on summer squash crops. Although the overall parasitism rate was about 11%, this differed greatly by year and over the course of the season, suggesting that augmentation (rearing and releasing the beneficial wasps) in early summer could be valuable in most years, and that this effect would persist over the season. This natural enemy and its potential management for biological control of squash bugs may assist vegetable farmers, pest managers, and researchers involved with squash and related cucurbit crops. ABSTRACT: This study evaluated parasitism rates by Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) on the squash bug Anasa tristis DeGeer (Hemiptera: Coreidae) over a six-year period in squash fields in Maryland. From 2016–2021, 2226 wild squash bug egg masses were collected, 2180 (98.0%) A. tristis egg masses and 46 (2.0%) A. armigera egg masses. The mean (±SE) parasitism rate was 10.9 ± 0.16%. Yearly parasitism rates were significantly different with rates in 2017 and 2018 that were significantly lower than in 2019, 2020, and 2021. The significant difference in parasitism rates based on planting date was primarily due to the high parasitism rate observed in 2021. These results suggest that the use of augmentative releases early in the season could result in effective control by increasing parasitism earlier in the season and by causing the parasitism rate in the field to peak at a higher number late in the season.