Reducing early season cucumber beetle pressure with a semiochemical augmented trap-out approach

Commodities

Practices

To address the challenges of managing striped cucumber beetles sustainably, this project proposes a pheromone-based trap-out technique designed to significantly reduce beetle populations during the critical early season growth stage of cucurbit plants. By leveraging the beetles' chemical ecology and acute sensitivity to semiochemicals, we aim to provide growers with a targeted, cost-effective, and environmentally responsible alternative to conventional chemical controls.

Our research from 2023 showed that augmenting vittatalactone (the striped cucumber beetle aggregation pheromone) baited clear sticky traps with floral lures containing indole, or a 3-part blend of indole, trans-cinnamaldehyde, and tri-methoxybenzene (TIC) significantly increased beetle capture (Figure 1). Early concerns that the addition of a floral volatile might increase pollinator bycatch were assuaged by results that revealed pollinator captures over the 6-week period were not affected by the addition of floral compounds (Figure 2). Additionally, captures of bumble bees (Bombus spp.) were minimal, and captures of squash bees (Xenoglossa pruinosa) were non-existent. Since these are the most significant pollinators of many cucurbits (Hurd & Linsley, 1964; McGrady et al., 2020), this is very promising, as these insects can be severely affected by traditional spray regimes (Scott-Dupree et al., 2009; Willis Chan & Raine, 2021).  As this strategy is targeted early in the growing season, we largely avoid impacting many pollinators, and such impacts can further be mitigated with strategic trap placement away from floral resources that the bees make use of.

[caption id="attachment_1187191" align="alignnone" width="300"] Figure 1: Mean total captures of striped cucumber beetles per trap over a 6-week period from April-June in 2023, by lure. Treatments include Indole, vittatalactone (VT), trimethoxybenzene/indole/trans-cinamaldehyde blend (TIC), and combination VT-TIC and VT-Indole lures. General linear mixed-effect model, Post-Hoc Tukey Test (p<0.05)[/caption] [caption id="attachment_1187192" align="alignnone" width="300"] Figure 2: Mean total captures of all pollinators per trap over a 6-week period from April-June in 2023, by lure. Treatments include Indole, vittatalactone (VT), trimethoxybenzene/indole/trans-cinamaldehyde blend (TIC), and combination VT-TIC and VT-Indole lures. Compounds did not majorly influence captures. General linear mixed-effect model, Post-Hoc Tukey Test (p<0.05)[/caption]

The proposed solution focuses on a pheromone-based trap deployment system designed to manage cucumber beetle infestations as early and effectively as possible while addressing broader goals of sustainability and accessibility. At its core, the system deploys synthetic vittatalactone paired with indole, a cost-effective and widely available floral volatile, to bait traps that attract and capture the overwintering generation pf striped cucumber beetles before they establish on vulnerable cucurbit seedlings in spring. This early intervention reduces beetle populations during the most critical growth period, preventing yield-reducing damage and disease transmission in cucurbit crops. By targeting pests during their pre-establishment phase, this approach is more precise and species specific than many other forms of pest control.

We aim to reduce or eliminate the need for continuous chemical applications throughout the summer, aligning with sustainable agriculture goals by lowering input costs and reducing environmental impact. By reducing reliance on neonicotinoids and pyrethroids, this strategy minimizes risks to pollinators, natural enemies, and other non-target species, fostering healthier ecosystems and reducing the development of insecticide resistance and secondary pest outbreaks. It may also offer significant economic advantages by lowering input costs for growers, replacing expensive chemical regimens with a straightforward and cost-effective trapping strategy suitable to smaller or less advantaged growers, and providing a critical tool for organic growers who lack access to chemical control options. By targeting pest populations during the most vulnerable growth stage, this approach also helps safeguard crop yield and quality.

Beyond its direct agricultural impacts, this solution advances environmental sustainability by preventing biodiversity loss from excessive pesticide usage. Through close collaboration with local growers, particularly those serving underserved communities, this project aligns its methods with real-world needs, promoting equitable access to sustainable pest management practices. On-farm trials, spatial analysis, and refined trapping protocols will further demonstrate the feasibility and effectiveness of this approach, and with a year of data already collected, results already seem promising. Ultimately, this work has the potential to transform striped cucumber beetle management in the southern United States, advancing sustainability and resilience in agricultural systems while reducing ecological and economic burdens for farmers and their communities.

Objective 1: Determine if early season trap-out reduces striped cucumber beetle pressure on cucurbits

To demonstrate potential benefits of pheromone-based trapping for small-scale local growers, we are collaborating with farmers around southwestern Virginia. In 2024 we collected our first year’s data and established 8 field sites. 4 sites received the trap-out treatment, and 4 served as controls. The trials were divided into two phases:

1. Trapping Phase (April - June): Baited traps capture the overwintered generation of striped cucumber beetles before competition from flowering cucurbits. Sticky cards mounted horizontally on wooden stakes, baited with vittatalactone-indole lures replaced biweekly. Beetle captures counted weekly to assess impact of baited traps on beetle populations.
2. Monitoring Phase (June - August: Un-baited sticky traps evenly spaced in cucurbit plots to monitor relative beetle densities between treatment and control sites. Four traps per plot replaced every two weeks.

Baited traps were generally spaced 50 feet apart along fence edges and tree lines close to the historic cucurbit plots.

The impact of the vittatalactone-indole baited traps on beetle populations was analyzed using a linear mixed-effects model (LMER), with treatment, date, and their interaction as fixed effects, and field site as a random effect. We found significant reductions to cucumber beetle populations across the monitoring phase in trapping sites (coefficient = -69.38, SE = 14.90, z = -4.66, p < 0.001), with daily mean beetle populations in trapping sites remaining well below control sites until late July, even as baited traps were removed in June as crops blossomed (Figure 3). If funded, a similar effort across additional locations will be attempted to see if results can be replicated or improved.

[caption id="attachment_1187235" align="alignnone" width="300"] Figure 3: Mean captures of beetles between locations that received early season trapping effort (Trapping) and control during the monitoring phase of the study. * = (p<0.05) via post hoc TK test.[/caption]

Objective 2: Understand the early-season spatial ecology of cucumber beetles

To better understand the relationship between landscape features and cucumber beetle captures in the early season, we designed a landscape study across four sites at three contiguous organic farms in Floyd, VA. Our goal is to understand the relationship between beetle captures of the overwintered generation and the distances of traps from potential overwintering habitats like tree lines and old cucurbit fields.

Each site featured 15 vittatalactone-baited ground-mounted boll weevil traps with neonicotinoid treated netting placed inside as the killing agent, resulting in 60 traps in total. This method was validated as the most effective non-sticky trap by Pasteur et al. (2023). The traps were placed on square-foot shingles secured with landscape fabric staples, with a 5-foot-diameter halo cut around each trap to enhance their visibility. Each field has three parallel transects (Figure 4):

• The inner transect runs along the tree line.
• The middle transect runs through the field center.
• The outer transect is on the opposite side.

Across each transect axis, the traps are arranged symmetrically:

• The central trap aligns with the field's centerline.
• Two traps on either side of the center are positioned toward the edges, with additional traps placed at equal distances beyond the field edges.

The distribution of trap captures was monitored over eight weeks, spanning beetle emergence until the flowering of cucurbits.

[caption id="attachment_1187236" align="alignnone" width="353"] Figure 4: Diagram of trap layout. X = the distance from plot center point to edge traps positioned immediately outside plot margins to define trap spacing within transect. Y = the distance between the inner transect along the tree line and the nearest margin of previous year's cucurbit plots to define spacing between transects.[/caption]

Multiple regression analyses will assess spatial and environmental factors impacting beetle captures. The dependent variable will be beetle counts per trap, while independent variables include distances from the plot center, tree lines, transect position, and proximity of recorded floral resources. Weekly heatmaps will visualize the beetle distribution to observe dispersion patterns, revealing how beetles may become diffuse as they leave their overwintering sites. This experiment will clarify beetle-landscape relationships and inform the strategic placement of traps on farms where trap saturation might not be feasible.

Analysis is ongoing, but early heatmapping does suggest a relationship between beetle captures and the edge of the trapping area near trees and floral resources (Figure 5)

[caption id="attachment_1187240" align="alignnone" width="300"] Figure 5: Heatmap of striped cucumber beetle captures in 2024 at Riverstone Organic Farm in Floyd, VA. White dots indicate trap placement across and around a field that held zucchini production during the 2023 season.[/caption]

Objective 3: Determine the trapping radius of vittatalactone and indole-baited traps

Using the mark-release-recapture (MRR) technique developed by Miller et al. (2015), we aim to evaluate cucumber beetles' response to pheromone-baited traps across varying distances. This approach, coupled with estimates of their flight dispersal capacity, will provide critical insights into the effective trapping radius of semiochemical-baited traps in environments lacking cucurbit hosts.

Beetles were collected from cucurbit farms using commercially available hand vacuums modified to safely capture insects. Preliminary trials confirmed that fluorescent powder marking did not impair beetle survival or mobility and remained visible for at least 24 hours. Marked beetles were released at dawn in a flat, mowed field, far from competing host signals. At the field's center, a sticky card trap baited with vittatalactone-indole lures was placed, surrounded by release cages arranged in concentric rings. Release distances ranged from 1 to 15 meters, with the number of beetles released at each distance adjusted to maintain an equal density of beetles per unit area of each annulus. Unique colors were used to mark beetles at each distance, and captures were recorded at 24 hours, and 5 releases at varying distances occurred over a month-long period.

Combining these data with dispersal capacity estimates derived from past and future flight mill trials will determine the trapping radius and optimize trap deployment strategies. Trials from this previous year will be repeated next year to improve statistical power and ensure repeatability.

[caption id="attachment_1187244" align="alignnone" width="300"] Figure 6: Beetle captures and release distance plotted alongside a fitted exponential decay model.[/caption]