The squash bug, Anasa tristis De Geer (Hemiptera: Coreidae), is a serious pest of cucurbit crops across the US, especially within summer squash (Cucurbita pepo L.) systems. Using its piercing sucking mouthparts, squash bug feeds on both leaf tissue and fruits, potentially leading to leaf necrosis, seedling death, and yield loss. Currently, A. tristis management strategies in summer squash focus exclusively on insecticide applications. Given that continuous use of insecticides imposes negative side effects on many non-target species, the major objective of this dissertation was to identify new and understudied management strategies for minimizing A. tristis damage in Virginia summer squash. To accomplish this goal, we first performed experiments to test the effects of colored mulches on squash bug density. A two-year field replicated study conducted in 2019 and 2020 in southwest Virginia found that black, white, and reflective plastic mulch colors had no effect on squash bug adult, egg mass, or nymphal densities. Overall, we observed a broad plastic mulch effect, as summer squash plants grown in any plastic mulch color tended to harbor greater densities of squash bug life stages than plants grown on bare ground. Next, the potential of augmentative releases of egg parasitoid, Hadronotus pennsylvanicus Ashmead (Hymenoptera: Scelionidae) was assessed by deploying lab-reared parasitoids on organic farms growing summer squash in southeastern Virginia in 2020 and 2021. In both years, we found higher levels of A. tristis egg parasitism at H. pennsylvanicus release sites compared to sites where the parasitoids were not released. Further, higher egg parasitism at the release sites was observed within two weeks of the field deployment date. The third goal of this dissertation research was to characterize the relationship between squash bug life stages and marketable summer squash yield. In 2020 and 2021, summer squash fields were established in Whitethorne, Virginia and individual plants were labeled as either 'managed' or 'infested'. Managed plants were subject to weekly manual removal of all squash bug egg masses and nymphs, while infested plants were left to have natural densities of squash bug life stages. We performed weekly A. tristis surveys on all infested plants in both years and added H. pennsylvanicus surveys on infested and managed plants in 2021. Also, we collected all fruit produced by each plant. Managed plants were found to produce more marketable fruit and fewer squash bug-damaged fruit than infested plants. Linear regression analyses of initial two-week accumulated squash bug life stage counts displayed adult and nymph densities to be significantly associated with marketable fruit yield per plant. However, nymphs showed a considerably stronger relationship with marketable yield than did adults. Hadronotus pennsylvanicus was visually sampled during each of the eight sampling weeks, but did not exhibit high egg parasitism until the latter half of the sampling interval. Lastly, we evaluated the toxicity of reduced risk insecticides on A. tristis nymphs and H. pennsylvanicus adults. To do so, we conducted laboratory bioassays exposing nymphs to insecticide treated summer squash fruit and parasitoids to treated filter paper, and recorded mortality at 24, 48, and 72 h following initial exposure. Only one reduced risk insecticide, flupyradifurone, was found to be highly toxic to squash bug nymphs and nontoxic to the parasitoids. Overall, the results of these studies will offer much needed information to improve the success and sustainability of squash bug management programs, as well as provide a fundamental basis and spark motivation for future research in squash bug biological control.
Doctor of Philosophy
The squash bug is a serious insect pest of summer squash across the United States. Squash bugs inflict damage by feeding on plant leaves, stems, and fruits, leading to significant reductions in fruit yield and overall economic losses for growers. To date, farmers have few useful tools to minimize squash bug damage in their summer squash crop, and resort to over-applying insecticides. While this use of insecticides helps lower squash bug numbers, it often has negative side effects on the environment and important beneficial insect species like pollinators. To better understand the squash bug as a summer squash pest and to promote nonchemical ways to reduce squash bug damage, this dissertation research pursued answers to questions regarding: (1) the effect of plastic mulch color on squash bug numbers, (2) the use of squash bug natural enemies to control squash bugs, (3) the relationship between numbers of squash bugs and damaged summer squash fruits, and (4) whether new types of insecticides can control squash bugs and also be safe for beneficial insects. The results of this research will provide new insights on current issues with squash bug pest management. In particular, this work will provide summer squash farmers with useful knowledge that can be applied to their future efforts to responsibly control squash bugs in their fields and maximize their crop yields. With more research-supported and sustainable squash bug control tools, farmers will be able to not only adopt more environmentally-friendly food production practices, but also lower their overhead farm management costs and ultimately provide higher quality squash to consumers.