The impact of a squash bug egg parasitoid and its sensitivity to selective insecticides

The squash bug, Anasa tristis DeGeer (Hemiptera: Coreidae), is a native pest of cucurbit plants throughout the United States.  Gryon pennsylvanicum Ashmead (Hymenoptera: Platygastridae) is a squash bug egg parasitoid found in Virginia and the surrounding states.  Squash bug egg masses were collected across Virginia in 2014 and 2015 showed G. pennsylvanicum to be an important natural enemy of squash bug.  An integrated cucurbit pest management program would need data on the risk that common practices may pose to this natural enemy.  Egg masses that were likely parasitized were used in an insecticide bioassay.  Masses were dipped in field rate mixtures of insecticides that were chosen because of their efficacy on squash bugs, and other pests of cucurbits such as aphids (flupyradifurone, pyrifluquinazon, flonicamid, sulfoxaflor).  Lambda-cyhalothrin was also included because it is commonly used in cucurbit production, and broad-spectrum insecticides are known to pose a risk to natural enemies.  Egg masses were allowed to hatch and numbers of emerging squash bug nymphs and egg parasitoids were recorded.  The resulting data were analyzed using a chi square goodness of fit test, where the controls from each of the nine trials served as a representative of parasitization levels for each site and was used as the “expected” values in our analysis.  None of the insecticides significantly reduced parasitoid emergence from squash bug eggs when compared to the water treated control, suggesting that the eggs are a safe environment for both host and parasitoid.