Nymphal abundance is best predictor of squash bug damage to zucchini.

Current pest management decisions for squash bug, Anasa tristis (Hemiptera: Coreidae), a key cucurbit pest in North America, are based on counts of adults and egg masses. Nymphs contribute strongly to crop damage and are the life stage most vulnerable to insecticides, and therefore are considered an important target for effective chemical-based integrated pest management. In order to identify which life stage most accurately predicts future yield, we evaluated the relationship between different squash bug life stages and marketable summer squash yield. In 2020 and 2021, we conducted weekly counts of all life stages for 6 to 8 wk in Virginia zucchini fields. Individual plants were randomly labeled as either "managed" plants (all egg mass and nymph stages manually removed) or "infested" plants (no life stages removed). In 2021, we also observed presence or absence of the egg parasitoid Hadronotus pennsylvanicus Ashmead (Hymenoptera: Scelionidae) on infested plants and performed an egg parasitism assessment using the removed egg masses from managed plants. Marketable and damaged fruit were collected from each plant 3×/wk for 3 wk. In both years, managed plants produced significantly more marketable zucchini and fewer squash bug-damaged fruit. Regression analyses found accumulated nymph counts were negatively correlated with number of marketable fruit. Hadronotus pennsylvanicus was present on infested plants during every sampling week, with elevated parasitism rates observed only during the latter half of sampling. This study sheds new light on the relationship between A. tristis densities and marketable summer squash yield and offers a strong basis for which more reliable squash bug thresholds can be elucidated.