Effect of squash bug life stages on marketable yield in zucchini

Authors: Boyle, Sean; KUHAR, THOMAS - Virginia Tech; Weber, Donald

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2025
Publication Date: 8/18/2025
Citation: Boyle, S.M., Kuhar, T., Weber, D.C. 2025. Effect of squash bug life stages on marketable yield in zucchini. Journal of Economic Entomology. https://doi.org/10.1093/jee/toaf111.
DOI: https://doi.org/10.1093/jee/toaf111

Interpretive Summary: Squash bugs are key pests of cucurbit crops in eastern North America. They prefer, and are especially damaging to, squash, zucchini and pumpkins of the “pepo” species. Since cucurbits are bee-pollinated, pest management must not use insecticides which are unnecessary or those that negatively affect the essential pollinators. Knowledge of economic thresholds, and the relationship of pest numbers to crop damage, is an important component of cucurbit integrated pest management. Current thresholds are poorly supported by science, and are based on adult and egg counts, not reflecting the importance of damage by nymphs, the squash bug’s immature stage. This study determined the effect of squash bug infestation at different life stages, on damage to harvested zucchini, by manipulation of squash bug numbers and quantification of quality effects in zucchini yield. Harvest analysis pointed to nymphal counts showing a much stronger relationship to crop damage than did adult counts. The beneficial egg parasitoid Hadronotus pennsylvanicus was present on infested plants during every sampling week, and offers significant suppression of squash bug numbers in the field. This study contributes to development of scientifically based thresholds, which will be useful to vegetable pest managers, researchers and extension personnel as a basis for reliable and pollinator-safe cucurbit pest management.

Technical Abstract: 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 an important target for effective chemical-based IPM. For this reason, we evaluated the relationship between different squash bug life stages and marketable summer squash yield. In 2020 and 2021 Virginia zucchini, we counted all life stages weekly for 6-8 weeks. 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 3x/week for three weeks. In both years, managed plants produced significantly more marketable zucchini and fewer squash bug-damaged fruit. Regression analyses found accumulated adult and nymph counts were negatively correlated with number of marketable fruit, with nymphal counts showing a much stronger relationship. 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.