Attract-and-Kill Strategies for Sustainable Striped Cucumber Beetle Management

Progress report for LNE20-413R

Project Type: Research Only
Funds awarded in 2020: $180,315.00
Projected End Date: 02/28/2023
Grant Recipients: UNH Cooperative Extension; University of Vermont; USDA-ARS
Region: Northeast
State: New Hampshire
Project Leader:
Dr. Anna Wallingford
UNH Cooperative Extension
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Project Information

Summary:

Problem, Novel Approach and Justification:

Striped cucumber beetle (SCB) is a serious pest of cucumber, melon, squashes, and pumpkin. While effective chemical controls are available in conventional systems, concern for pollinators visiting these pollinator-dependent crops has driven demand for non-chemical or bee-safe alternatives. Behavioral controls can replace chemical controls, or be integrated with other tools and tactics to achieve control with a dramatic reduction in insecticide use and unwanted non-target effects.

Attract-and-kill (A&K) approaches lure pest insects to a source of poison, which is often combined with an arrestant or feeding stimulant. Here we seek to develop and field test an A&K approach using SCB aggregation pheromone (vittatalactone) to lure beetles to a bait station containing a feeding stimulant (cucurbitacin) laced with a gut poison (spinosad).

Research Plan:

Experiments will address questions regarding trap development and issues with trap deployment, like how much area around traps is affected and how long components of our traps will last in the field (NH, MD). Experiments will also include field-scale evaluations of our system in collaboration with farmers in NH, VT, and ME.

Outreach Plan:

This project will generate peer-reviewed and editor-reviewed manuscripts that contribute to our understanding of insect behavior and pest management. In addition to generating extension publications, research results will be presented at grower presentations, twilight meetings, field days, and through direct transfer of information to growers in one-on-one interactions.

 

Project Objective:

The ultimate goal of this project is to develop an effective and adoptable attract-and-kill (A&K) approach for managing striped cucumber beetle (SCB), using attractive odors, selective feeding stimulants, and the judicious use of bee-safe insecticides.

Project Objective:

The ultimate goal of this project is to develop an effective and adoptable attract-and-kill (A&K) approach for managing striped cucumber beetle (SCB), using attractive odors, selective feeding stimulants, and the judicious use of bee-safe insecticides.

Introduction:

2020 Progress

The ultimate goal of this project is to create a sink in cucurbit pest populations by luring striped cucumber beetle (SCB), Acalymma vittatum F. (Coleoptera: Chrysomelidae) to baited trap, where they are captured and/or killed.

While adult SCB will often consume nectar and pollen from a broader range of host plants, members of the Cucurbitaceae family are required for their successful reproduction. Adult beetles overwinter under leaf litter in wild habitats and emerge in the spring to feed and find mates. Eventually they move into cultivated cucurbit crops, often in response to crop flowering. Male striped cucumber beetles emit an aggregation pheromone, vitattalactone, that aids in attracting both male and female conspecifics to hosts as well. Females then lay their eggs at the base of their host plant, and the subsequent larvae burrow down in to the soil to feed on roots until the pupate and emerge in a new generation of adults. In the northeastern United States, SCB will typically complete two generations but longer seasons can allow for a third generation from time to time.

Male striped cucumber beetles emit an aggregation pheromone, vittatalactone (2-methyl-3-(2,4,6,8 tetramethyloctyl) oxetan-3-one), when feeding on a favored host. Chauhan and Paraselli (2017) devised and patented a synthesis that produces eight stereoisomers of vittatalactone with the ring configuration (2R,3R), including the one active isomer. Mixed vittatalactone (eight stereoisomers of (2R,3R)-vittatalactone) has proved highly attractive to both sexes of SCB. This semistereospecific synthesis (i.e. that produce an isomeric mix at three chiral centers, of the five in the molecule) enables less expensive production of the SCB aggregation pheromone in quantities useful for field testing and application.

Mixed vitattalactone lures were found to attractive SCB, SpCB, and (surprisingly) squash bug adults and nymphs in preliminary testing during the fall of 2019. While replication is necessary to confirm this finding, our cheaper, “new and un-improved’ lure may be effective at management multiple key pests of cucurbit crops.

Concerns regarding COVID limited access to our research facilities in the spring of 2020 and university restrictions on our workers limited our ability to replicate several experiments. This has delayed our work on our first objective, understanding vicinity affects associated with bait stations. However, we were able to carry out several field experiments, which allowed our workers to conduct no-contact site visits to collect on-farm data. We have made steady progress in our second objective, to evaluate our Attract & Kill approach in the field. We conducted a series of experiments to evaluate the power of our experimental lure and trap design.

Research

Materials and methods:

Dose-Response Trials.

Our lure contains a man-made version of cucumber beetle aggregation pheromone (vitattalactone), which evaporates from our trap to create an attractive odor plume. The potency of our lure could be affected by the concentration of this compound, which is affected by the initial dose applied to our lures. If the dose is too low, the beetles won’t be able to detect it. If the dose is too high, the beetles might not find it attractive.

In order to understand how the dose affects beetle response, we deployed clear sticky traps baited with various concentrations of vitattalactone in farmland with a history of cucumber beetle infestation (Beltsville, MD). We observed how many beetles were trapped weekly. We also changed traps, refreshed lures, and re-randomized treatment locations to replicate the experiment in the spring and fall of 2020.

 

Trap Design Trials.

Our lure is a powerful attractant for striped cucumber beetle, spotted cucumber beetle, and squash bug but we must identify a reliable method of capturing or killing the pest insects lured to our man-made aggregation.

In order to identify the best trap, we deployed various trap types in farmland with a history of cucumber beetle infestation (Beltsville, MD). Traps were baited with 1 mg vitattalactone, unless they were un-baited as a control. We observed how many beetles were trapped weekly. We also changed traps, refreshed lures, and re-randomized treatment locations to replicate the experiment.

 

Season-long Lure Trials.

We deployed 8 sticky traps at each of two commercial farm sites in Newmarket & Rollinsford, NH through the 2020 growing season.  Half of these traps were baited with 1 mg vittatalactone lures and the other half were unbaited as control. We changed traps, refreshed lures, and re-randomized treatment locations to replicate the experiment through the growing season. We also observed several crops for beetle densities through this same period.  At least 20 plants of each crop type were observed each week for the number of striped cucumber beetles, the number of spotted cucumber beetles, the number of squash bug egg masses, nymphs, and adults, signs of injury, and signs of bacterial wilt. We observed the undersides of leaves for at least 30 seconds per plant, if not all leaves. We supplied weekly reports of pest observations to growers, who treated all plants according to their wishes.

Early-Season Intervention Trials.

At three farms (VT, NH, ME), we deployed vitattalactone-baited boll weevil traps in the perimeter of one side of a plot of winter squash to see if early season trapping would remove enough pest insects from the system to result in different pest densities on plants through the season. Traps were 10 m apart and the “treatment” end of each field was at least 50 meters from the “control” end. Weekly visits were made to each site to scout each side of each field for striped cucumber beetles, spotted cucumber beetles, and squash bug egg masses, nymphs, and adults. For each field, we observed the number of beetles on 20 plants on the perimeter and 20 plants in the interior of each plot. The undersides of the leaves were examined on each plant for at least 30 seconds. We supplied weekly reports of pest observations to growers, who treated both plots according to their wishes, and growers supplied us with their spray records at the end of the season.

Research results and discussion:
 
  • Dose-Response Trials.

We concluded the following (Figs. 1 & 2):

  • An initial dose of 1 mg vitattalactone is appropriate for further testing.
  • We found a positive linear dose-response for striped cucumber beetle, spotted cucumber beetle, and squash bug, with no signs of repellency in high concentrations.
  • This dose-response is strongest in the early season, before host plants are present.

Figure 1. Number striped cucumber beetles observed on clear sticky traps, baited with vitattalactone lures of various doses (Beltsville, MD).
Figure 2: Number spotted cucumber beetles or squash bug adults observed on clear sticky traps, baited with vitattalactone lures of various doses (Beltsville, MD).

 

Trap Design Trials.

We concluded the following (Fig. 3):

  • We found that sticky traps, boll weevil traps, and yellow gallon jug traps captured more striped cucumber beetles than unbaited traps, and captured more beetles than other baited designs.
  • Given concerns regarding non-target trapping of beneficial hymenopterans, we opted not to use yellow sticky cards or yellow gallon jug traps in further testing, and continued our testing with clear sticky cards and boll weevil traps.
Figure 3. Mean number (+/- SEM) striped cucumber beetles captured by various trap designs, un-baited or baited with 1 mg doses of vitattalactone (Beltsville, MD).

 

Season-long Lure Trials.

We concluded the following (Fig. 4 & 5):

  • When there are not actively growing crops, significantly more beetles were captured by baited traps than un-baited controls.
  • Stimuli from crop plants likely outcompete our man-made attractants at this trap density.

Figure 4. (Above) Mean number (+/- SEM) of striped cucumber beetles captured by clear sticky traps baited or un-baited with 1 mg dose vitattalactone lures. Asterisk indicates significant different according to t-tests. (Below) Mean number of striped cucumber beetles observed on crop plants. (Newmarket, NH)
Figure 5. (Above) Mean number (+/- SEM) of striped cucumber beetles captured by clear sticky traps baited or un-baited with 1 mg dose vitattalactone lures. Asterisk indicates significant different according to t-tests. (Below) Mean number of striped cucumber beetles observed on crop plants. (Rollinsford, NH)

 

Early-Season Intervention Trials.

This experiment has not yet been replicated in a sufficient number of instances to make conclusions on whether or not our experimental approach creates a significant sink in cucurbit pest populations. While we captured economically threatening number of beetles at all three sites during the early part of the season, the pest pressure at our ME site was too low to include in analysis.

 We have concluded the following (Fig. 6):

  • Although we have not collected enough data on whether or not this approach contributes to pest management of this crop, we feel like we’ve collected enough information to conclude that creating man-made aggregations will not make pest pressure worse than no action. This assertion will make recruiting new collaborating farmers easier as the project continues.
  • The boll weevil trap fell short of expectations in terms of successful trap capture rate. In several instances, we found beetles on traps or near traps rather than inside traps. Future Early-Season Intervention Trials will be continued with attract-and-kill bait stations.
Figure 6. (Above) Mean number (+/- SEM) of striped cucumber beetles observed on crop plants at NH & VT sites. (Below) Mean number of striped cucumber beetles captured by vitattalactone-baited boll weevil traps, one week before planting and four weeks following planting at ME, VT, NH NH winter squash farm sites.
Research conclusions:

Year one experiments need replication before making recommendations.

Participation Summary
5 Farmers participating in research
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.