- Vegetables: cucurbits
- Crop Production: no-till
- Pest Management: biological control, chemical control, integrated pest management
Squash bug is a major pest of squash and pumpkin in the U.S. Current control tactics involve insecticide applications that are injurious to pollinators and natural enemies. Based on a 3-year survey in Virginia and surrounding states, we found that >50% of squash bug egg masses were parasitized by the parasitic wasp, Gryon pennsylvanicum. We also evaluated the toxicity of various reduced risk insecticides to the parasitoid and squash bug and found that neither flupyridafurone, pyrifluquinazon, flonicamid, nor sulfoxaflor controlled squash bug nymphs as well as the pyrethroid, lambda-cyhalothrin, which was also the most toxic to the parasitoid adults.
The squash bug, Anasa tristis DeGeer (Hemiptera: Coreidae), is an important pest of pumpkin (Cucurbita maxima) and squash (C. pepo) causing wilt in plants with its piercing-sucking mouthparts and by potentially vectoring Cucurbit Yellow Vine Decline (Bruton et al. 2003, Doughty et al. 2016). Many commercial growers of these crops typically apply broad-spectrum foliar insecticides, commonly pyrethroids (often tank-mixed with fungicides) ( Doughty et al. 2016). Cucurbits are pollination dependent and many of the registered insecticides recommended for use in commercial cucurbit production are known to be acutely toxic to bees (Agency 2015, Wyenandt et al. 2016). Beyond pollinators there are other organisms that may be impacted by pest management practices, for instance, natural enemies that could be keeping pests in check in cucurbit systems.
Egg parasitoids, in particular, are important natural enemies of heteropteran pests. Out of the native egg parasitoids of A. tristis, Gryon pennsylvanicum Ashmead (Hymenoptera: Scelionidae), has been found to have the highest fecundity and rate of reproduction than three other encyrtid wasp species that also attack squash bug (Nechols et al. 1989). Gryon pennsylvanicum also appears to be widespread in North America and was reported to occur in the mid-Atlantic U.S. as early as 1943 (Schell 1943). This scelionid wasp has a host range that is limited to the leaf-footed bugs (family Coreidae), and has been recently introduced as a classical biological control agent for the western conifer seed bug in Italy (Peverieri et al. 2013, Roversi et al. 2014). Plant hosts can play a potential role in the capacity of A. tristis to lay eggs (Bonjour et al. 1990), overall survival (Bonjour and Fargo 1989), and squash bug reproduction (Bonjour et al. 1993), without effect on the parasitization of G. pennsylvanicum (Vogt and Nechols 1993). Adult G. pennsylvanicum do not feed on the host eggs (Vogt and Nechols 1993), but rather feed on the exudate from cucurbit leaf trichomes (extra-floral nectaries) that serve as sources of basic sugars and protein (Olson et al. 1996). The feasibility of augmentative biological control has been explored, but Olson et al. (1996) found that it was not economically feasible compared to chemical control. Nonetheless, it is important to assess the natural control impact of this parasitoid. In Kentucky, Decker and Yeargan (2008) observed egg parasitism as high as 31% with G. pennsylvanicum as the predominant egg parasitoid. More recently, Cornelius et al. (2016) observed high rates of parasitism by this species in Maryland, particulalry later in the season. To our knowledge a survey of squash bug egg parasitism has not been conducted in Virginia. Herein, we report the results of a three year survey from 31 counties throughout Virginia and surrounding states to allow us to quantify the potential effects egg parasitism may have on squash bug population dynamics.
In addition we evaluated the efficacy of various reduced risk insecticides for control of squash bug and toxicity to the parasitoid.
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Project objectives:div style="margin-left:1em;">
Objective 1: To survey the egg parasitoids of squash bugs throughout Virginia.
- Collections of squash bug egg masses
- The specimens collected will be taken to the Virginia Tech Vegetable Entomology Lab and reared in environmental chambers for identification to species where possible. Records of location, host plant, parasitism levels, and squash bug hatch rate will be made.
Objective 2: To assess the effects of narrow-spectrum insecticides on the eggs and nymphs of squash bug and its egg parasitoid.
Egg masses collected will be utilized in screening assays to by location. Assays will screen for effects of specific narrow-spectrum insecticides against the controls and a commonly used broad-spectrum insecticide. The controls will provide baseline data on the parasitism levels and squash bug hatch rates for each location. The assay will be structured as follows:
Bioassay replicated 5 to 6 times. For each rep per treatment, 1o egg masses will be dipped in treatments.
Treatments : water control, Lambda-Cyhalothrin, flupyridafurone, Pyrifluquinazon, Flonicamid, and Sulfoxaflor
All treatment concentrations will be at maximum label rate
Assays were replicated as masses became available