Final report for GNC21-329
Project Information
Popillia japonica Newman (Coleoptera: Scarabaeidae) feeding negatively impacts many plant species, including grapes, potentially reducing fruit quality and yield. Chemical control, representing the current grower standard, relies on frequent broadcast applications of broad-spectrum insecticides, with alternative management strategies mostly lacking. Attract-and-kill (A&K) is a behavioral management strategy that combines semiochemical attractants and a killing agent on a substrate. This study assessed the impact of A&K on P. japonica in Wisconsin vineyards, with objectives to (1) assess the impact of A&K on the number of P. japonica adults in vineyards, and (2) assess the impact of A&K on P. japonica feeding injury to grape foliage compared to the grower standard. This two-year study was conducted at four commercial vineyards with a grower standard control and an A&K treatment. The A&K treatment consisted of commercial lures, each placed on outside-edge grapevines and weekly applications of carbaryl on the plants holding lures, while the grower standard received neither. The A&K treatment experienced similar numbers of P. japonica adults and proportions of leaf injury compared to the grower standard. The use of A&K reduced by 96% the crop area treated with insecticides compared to the grower standard. The area treated by A&K was at the edge of the vineyards where more leaf injury occurred regardless of treatment. Attract-and-kill is a targeted approach that was effective at managing P. japonica and reducing chemical inputs on a small scale. It has potential to be scaled up and refined to provide growers with a new management strategy.
The expected learning outcomes for this project are as follows: 1) researchers and grape growers will learn how A&K compares to current grower standard practices for JB management; 2) researchers and grape growers will learn how A&K impacts bee abundance and diversity compared to current grower standard practices. The expected action outcomes of this project are as follows: 1) grape growers will start implementing A&K in their vineyard as a management strategy for JB; 2) using A&K, grape growers will experience JB management results comparable to that of current management practices, while decreasing the negative effects of pesticide applications.
Research
Study Sites and Sampling Periods
This study occurred over two years at three commercial vineyards, all located in south-central Wisconsin. Each vineyard grew various wine-grape cultivars and maintained their own crop and pest management practices during the span of this study. Sampling occurred from July 26 to August 27, 2021 and July 5 to August 26, 2022, before grape harvest to not interfere with harvest and because management of P. japonica ceases at harvest.
Experimental design
This study consisted of a paired randomized block design with four blocks in each year, with two vineyards each receiving one block and the largest vineyard receiving two blocks. Each block consisted of two 0.2-hectare triangular plots of grape vines at the edge of vineyards, so that two edges were border rows, and plots were separated by a minimum of 150m within each block. Plots were randomly assigned to the two treatments 1) A&K, and 2) grower standard practices. In the A&K plots, the perimeter A&K row on two field edges received 13 point-source grape vines spaced 8m apart (Fig. 1). Each point-source vine received a P. japonica dual commercial lure (Trécé, Adair, OK) hung from an inner branch of the vine, 1.2m above the ground. Point-source vines were sprayed every 7-11 days depending on weather and vineyard activities, with a 44.1% Carbaryl insecticide (Sevin XLR PLUS, Tessenderlo Kerley Inc, Phoenix, AZ) at a rate of 2.3 l/hec. The insecticide was applied using a backpack sprayer (Dewalt, Baltimore, MD), and the A&K plots received no additional pesticide applications throughout the seasons. Grower standard plots were of the same dimensions as the A&K plots but received no P. japonica lures and insecticide sprays were applied at the discretion of vineyard managers as no actual economic threshold exists for P. japonica in vineyards. Pesticide application records were collected from each vineyard manager both years, with Carbaryl (44.1%), Zeta-cypermethrin (9.15%), and Fenpropathrin (30.9%) being applied during the sampling periods. A 10m wide buffer flanked the triangular plots inside the vineyard to reduce insecticide applications in the rest of the vineyard from impacting the A&K treatments.
Sampling of adult P. japonica
To compare the number of adult P. japonica present in A&K and grower standard plots, we recorded the number of adult beetles present on vines in each treatment. Each plot was split into three sampling rows, edge row, 2nd row, and inner row (Fig 1) to determine where beetles were most abundant within plots, and to compare between treatments. Three transects were conducted along the three sampling rows, with transects varying slightly in size to span the entire sampling rows. All adult P. japonica present on every vine in each row and on both sides of the vines were hand-collected, placed in sample bags, and frozen until they were counted in a laboratory. Sampling occurred weekly between the hours of 9:00 and 17:00 when there was low precipitation and wind.
Sampling of adult feeding injury
To compare injury to grape foliage between A&K and grower standard plots, we recorded the proportion leaf injury on vines in each treatment each week. In each treatment, 4 or 8 vines in each of the three sampling rows were randomly selected and surveyed, with the edge and 2nd row getting 4 vines on each edge of the plot. Vines were split into 4 sections, left and right of the trunk on either side of the plant. Each week, different vines and sections along each sampling row were randomly selected, as to not repeat a vine section in a given year. Leaves injured by P. japonica have a characteristic skeletonization pattern, and leaves having at least 10% of the leaf skeletonized were considered injured (Boucher and Pfeiffer 1989). Percent leaf damage was assessed by counting the number of injured leaves out of 40 leaves (Henden and Guédot, 2022). The leaves counted were on the closest shoot to the center of the vine, starting from the distal end. If 40 leaves were not present, the closest adjacent shoot was sampled as well to make up to 40 leaves (Henden and Guédot, 2022).
Mortality of P. japonica and bees at point-source stations
To compare adult P. japonica and non-target bee mortality at point source stations due to the attraction of the dual lures to bees, below each point-source vine we placed a 1m x 0.5m tarp wrapped around the grape trunk and stapled down to the ground to collect all killed insects that fell to the ground. Edges of the tarp were folded inward, to keep the insects from coming off due to weather and scavengers. Killed P. japonica were removed by hand from each tarp station weekly and hand-counted. Additionally, we counted the number of bees found on the A&K and grower standard tarp stations weekly and identified them to the furthest taxonomic level possible based on our ability.
Results
Popillia japonica adult abundance
The model that included treatment, year, and sampling location as predictors for the number of P. japonica adults per plant showed no significant difference between the A&K and the grower standard treatments (F2,288.66 = 1.65; P = 0.19; Fig. 2). Year had no effect on the number of P. japonica adults per plant (F1,8.45 = 0.04; P = 0.83) and there was a marginal difference in the number of adult beetles between sampling locations (F1,288.58 = 2.51; P = 0.08; Fig. 3). Pairwise comparisons, combining treatments, show no difference between edge row and inner row (P = 0.138; Bonferroni: P=0.413), a marginal difference between edge row and 2nd row (P =0.022; Bonferroni: P=0.066), and no significance between 2nd row and inner row (P = 0.418; Bonferroni: P=1.000).
Feeding injury
The model that included treatment, year, and sampling location as predictors of P. japonica feeding injury showed no significant difference between the A&K and the grower standard treatments (F1,4.21 = 1.31; P = 0.31; Fig. 4). Sampling year was marginally significant with a trend towards more injury in 2021 compared to 2022 (F1,7.92 = 4.40; P = 0.06). The sampling location had a significant effect on the proportion leaf damage (F2,274.92 = 22.61; P =8.11e-10; Fig. 5). Pairwise comparisons, combining treatments, show a significant difference between edge row and inner row (P = 0.013; Bonferroni: P= 0.039) and between edge row and 2nd row (P =2.6e-05; Bonferroni: P=7.9e-05), and no significant difference between 2nd row and inner row, (P = 0.077; Bonferroni: P=0.232) with the edge row having the most leaf injury.
Popillia japonica adult and bee mortality at A&K stations
The A&K stations had significantly more dead P. japonica (Mean ± SEM: 12,984 ± 1,601) beetles per station over 2 years compared to the grower standard (884 ± 86; t51=4.91; P= 9.784e-06). A total of 52,070 dead P. japonica were found in the A&K compared to 3,537 in the grower standard across the two sampling years. There were large differences between weeks, with a range of 674-9,870 beetles per week in the A&K and 0-821 per week in the grower standard. There were also large differences between vineyard, with one vineyard receiving 54.19% of the total dead P. japonica in the A&K.
Between the two sampling years, we collected a total of 17 dead bees in the A&K stations from 10 taxonomic groups, compared to 4 dead bees in the grower standard from four taxonomic groups. The A&K stations recorded Augochlora sp. (2), Andrena sp. (2), Apis mellifera (5), Bombus affinis (1), B. impatiens (3), B. pensylvanicus (1), Halicutus sp. (1), Lasioglossum spp. (2), and Triepeolus simplex (1). Grower standard stations recorded Augochlora sp. (1), A. mellifera (1), B. griseocollis (1) and Lasioglossum sp. (1).
Discussion
Our results show that A&K can be used to manage P. japonica in commercial vineyards as A&K resulted in equivalent numbers of P. japonica adults per plant and equivalent proportion of leaf injury on grapevines compared to the grower standard, which involved the broadcast application of 1-4 insecticide sprays targeted at P. japonica per season. The A&K stations at the edge rows recorded a 93% higher adult mortality compared to the grower standard stations and the edge row of vines had a higher proportion of leaf injury compared to the second and inner rows. Overall, the A&K reduced by 96% the area sprayed with insecticides compared to the grower standard.
Management of P. japonica in commercial crops relies primarily on insecticide applications. Our results suggest that A&K provided similar levels of P. japonica management compared to the current chemical grower standard. With the environmental and public pressure and governmental regulations to reduce pesticide applications on food crops, the emphasis is increasingly placed on alternative strategies to manage pests. Recently, studies are investigating behavioral strategies such as A&K and reported A&K to be successful at reducing pest insect numbers in different agroecosystems (Hafsi et al. 2016; Morrison et al. 2019), reducing crop injury (Hafsi et al. 2016; Chow et al. 2019; Morrison et al. 2019), and reducing egg production (Chow et al. 2019). Yet, A&K provided a lower level of control of onion maggot, Delia antiqua than the chemical grower standard (Willett et al. 2020). Here, the A&K led to equivalent number of beetles than the chemical grower standard known to be effective at reducing beetle numbers, while reducing by 96% the crop area sprayed with insecticides. The scale at which the A&K was applied and the fact that single plants were sprayed in the A&K treatment likely limited the impact the A&K had on beetle abundance. Future studies should investigate scaling up the area where the A&K is applied, spraying entire border rows in assessing the impact of A&K in different cropping systems.
Mass trapping implemented in elderberry and blueberry collected over 10 million beetles with little leaf damage to plants (Piñero and Dudenhoeffer 2018) and led to a 98% reduction in adult numbers compared to the previous year when implemented on isolated populations (Wawrzynski and Ascerno 1998). However, neither of these studies compared their results to background populations or considered yearly fluctuations in adult abundance and thus evaluating the impact of mass trapping in crop protection remains to be addressed. Further, mass trapping requires the setup of potentially large numbers of traps and regular servicing, which can be costly for growers and comes with the potential for trap spillover and saturation, which could lead to plant injury in the vicinity of the traps. On the other hand, the A&K point-source stations implemented here required low setup and maintenance input, as they only involve the hanging of P. japonica lures once per season and up to five insecticide applications to select plants on vineyard edges. Overall, while both mass trapping and A&K offer potential benefits and drawbacks for P. japonica management, growers should consider factors such as cost, effectiveness, and potential risks when deciding which method to use.
The implementation of A&K resulted in similar levels of leaf damage when compared to the grower standard. These results contrast with other studies in which A&K was shown to reduce fruit damage from C. capitata (Hafsi et al. 2016), D. suzukii (Klick et al. 2019), and H. halys (Morrison et al. 2019) compared to the grower standard. It is possible that the small-scale application of the A&K stations (13-point sources over 0.2 hec) in our study limited the impact on leaf injury. Future research should implement A&K at a larger scale, to entire perimeters of grape blocks to assess the feasibility and impact of defoliation to grape plants.
Vineyard edge rows saw more leaf damage, but not more beetles, than other sampling locations, supporting previous studies showing that P. japonica tend to aggregate at the edge of fields (Sara et al. 2013; Henden and Guédot 2022). The P. japonica lures are very attractive to adults and likely attracted beetles from around and within the vineyards (Henden 2020) as the beetles are capable of traveling long distances (Fleming 1972, Allsopp 1996). The increase in leaf injury in the edge row was not associated with more adults, indicating that the killing agent of the A&K, i.e., carbaryl, was effective at rapidly killing beetles attracted to the lures (Potter and Held 2002, Vitullo and Sadof 2007). The implementation of A&K on the outermost row of plants likely intercepted P. japonica entering vineyards as the A&K stations resulted in 94% more dead beetles than the grower standard stations. Insecticidal sprays targeted at perimeter edge rows can reduce pest species numbers within entire fields for species known to move into crops from the surrounding landscape, such as the plum curculio, Conotrachelus nenuphar (Johnson et al. 2002), H. halys (Morrison et al. 2019, Suckling et al. 2019) and P. japonica (Henden and Guédot, 2022, Sara et al, 2013), and focusing management strategies to these areas may result in reducing large fieldwide applications of insecticides.
The P. japonica attractants used in the A&K have been reported to kill thousands of bees caught in P. japonica baited traps (Hamilton et al. 1970, Sipolski et al 2019). Over the course of two summers, 21 bees were found dead under point-source stations, with 81% being recovered at the A&K stations. The application of broad-spectrum insecticides for the management of pests, such as P. japonica, can have detrimental effect on beneficial insects, including bees (Brittain and Potts 2011). Here, the A&K plots reduced the area treated with insecticides by 96% when compared to the grower standard, which consisted of 2-5 vineyard-wide applications of broad-spectrum insecticides, such as carbaryl and zeta-cypermethrin. The broadcasting of broad-spectrum insecticides at a vineyard-wide level likely results in high bee mortality (Shaw 1941), compared to the few bees being killed at A&K point-source stations, suggesting that A&K may be a better option for the conservation of bees compared to the grower standard in vineyards.
Overall, A&K offers a new management strategy for P. japonica in vineyards, comparable to the current grower standard, that lessens the chemical inputs, labor, and management costs to growers. Reducing the area sprayed with insecticide reduces the physical amount of insecticide needed to be purchased by growers, but also the time needed to be spent on application and the equipment needed for vineyard-wide sprays. The implementation of A&K in the outermost row is supported by our findings, and future studies are needed to scale this approach to entire fields, optimize the number of point-sources needed, the spacing between point-sources, and the best layout within a field to allow adequate implementation by stakeholders.
Educational & Outreach Activities
Participation Summary:
I did a 10-minute student presentation at the regional Entomology Society of America meeting in Vancouver, BC.
I did a 45-minute talk at the Wisconsin Fresh Fruit and Vegetable Conference in Wisconsin Dells, WI.
I did a 45-minute exit seminar at the University of Wisconsin- Madison.
Project Outcomes
The Japanese beetle is a major pest for many agricultural crops. Attract-and-kill is an alternative management strategy that provides the same level of management as current chemical control standards. Attract-and-kill for Japanese beetle lowers the area needed to treated by insecticides and the amount of insecticides needed, thereby reducing management efforts and economic expenditures by growers during the growing season.
Chemical applications are difficult to target to an individual species. When growers apply pesticides for JB, they are killing more than just this pest. Other insects, including declining pollinator species, may be negatively impacted. Attract-and-kill offers an alternative to these harmful vineyard-wide pesticide applications. This strategy potentially gives growers the opportunity to reduce non-target effects on pollinators, especially if they grow crops that require pollination, which could lead to higher rates of pollination and increased crop yield.
We learned how willing growers are to learn about and implement new pest management strategies that significantly differ from the grower standard. Knowing this information will help us and encourage us to develop more IPM strategies in the future.
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