DEVELOPING CULTURAL CONTROL TACTICS FOR SPOTTED WING DROSOPHILA MANAGEMENT IN SMALL FRUITS

• Sponsoring Institution: State Agricultural Experiment Station
• Project Status: TERMINATED
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 1009196
• Project No.: MD-ENTM-8989
• Project Start Date: Jan 19, 2016
• Project End Date: Jun 30, 2017

Project Director
Hamby, KE, A.

Recipient Organization
UNIV OF MARYLAND
(N/A)
COLLEGE PARK,MD 20742

Performing Department
Entomology

Non Technical Summary
Spotted wing drosophila (SWD) is a devastating invasive insect pest of soft-skinned fruits native to eastern Asia. It was first found in the mainland U.S. in 2008. Most large-scale farmers now apply broad-spectrum insecticides weekly when fruit are ripe in an attempt to manage SWD. These insecticides kill a wide variety of organisms, including beneficials such as pollinators. This is not an economically feasible management strategy for small farmers, and has dramatically impacted the sustainability of soft-skinned fruit production. Alternative management strategies are desperately needed. In this proposal we will gather the preliminary field biology data necessary to understand SWD distributions and habitat preferences within crops because effective use of cultural pest management strategies requires a sound understanding of pest biology. We will also evaluate cultural control practices such as canopy management and mulches for their potential as management tactics. Additionally, data obtained from this project will be used to obtain funding for an expanded research project, with the ultimate goal of developing sustainable and effective alternate management strategies that will lower production cost, and increase marketable yields and profits for fruit farmers while maintaining environmental stewardship.

Animal Health Component

0%

Research Effort Categories

Basic

40%

Applied

50%

Developmental

10%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
211	1120	1130	10%
211	1123	1130	10%
216	1129	1130	80%

Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants; 216 - Integrated Pest Management Systems;

Subject Of Investigation
1120 - Blueberry; 1129 - Berries and cane fruits, general/other; 1123 - Raspberry;

Field Of Science
1130 - Entomology and acarology;

Keywords

spotted wing drosophila

small fruit

cultural controls

pruning

mulches

Goals / Objectives
Drosophila suzukii, the spotted wing drosophila (SWD), is unique among Drosophila species, with a saw-like egg laying structure that is able to penetrate the skin of ripe or unripe fruit (Walsh et al. 2011). Since its initial U.S. invasion in 2008, SWD has devastated soft skinned fruit industries, especially blueberries, blackberries, raspberries, and cherries throughout the country. Losses due to SWD can be as high as 100% and have been valued at up to $718 million annually (eFly Working Group). SWD have an incredible reproductive capacity and short development time (Emiljanowicz et al. 2014). This, coupled with their broad host range makes them very difficult to manage at any farm (Walsh et al. 2011). Moreover, small farm operations are often most heavily impacted by SWD and are more likely to report total crop loss (eFly Working Group). Many Maryland fruit and vegetable farmers operate small (less than 200 acres), diversified farms with multiple SWD susceptible crops. In fact, even for a single fruit type these farms often have multiple plantings containing varieties that ripen at different times to lengthen their harvest season. This facilitates SWD population growth on farm and makes SWD management very difficult. Many farms have to apply weekly sprays of broad-spectrum insecticides that are dangerous to beneficial insects, e.g. bees, to achieve control of SWD. Alternative management strategies are desperately needed and effective use of cultural and physical pest management strategies requires a sound understanding of pest biology (Vincent et al. 2003).Environmental manipulation is a key cultural control tactic for managing insect pests (Pimentel 1961, Sprenkel et al. 1979). Recent research has shown that small differences in in-crop microclimate may result in significant differences in suitability for SWD (Tochen et al. 2015). The raspberry microclimate varies substantially within the canopy; in fact, the dense upper canopy can be 4.4°C cooler on warm days and 2.5°C warmer on cool days than ambient temperature (Willmer et al. 1996). In blueberries, pruning can impact the relative humidity within the canopy (Tochen et al. 2015), and variations in temperature and relative humidity significantly impact SWD population dynamics (Tochen et al. 2014, Tochen et al. 2015). Preliminary observations suggest that SWD infestation rates are higher within the center of plants grown on V-trellises compared to outer or upper portions of the canopy (Diepenbrock et al. unpub.). These microclimates likely differ in humidity, which will impact SWD survival and reproduction. Therefore, we will evaluate the ability of canopy management to reduce suitability of in-crop habitat to SWD (Obj.1). Field data (Woltz & Lee unpub.) from artificially infested and bagged fruit clusters (high SWD density situations) demonstrate that a large proportion of SWD drop out of fruit to pupate outside in the soil in Oregon. However, the extent to which this is true in other growing regions and population densities is unknown. Weed mats and mulches can be used in caneberries for weed control, and in blueberry production for weed control and managing soil pH. Mulches impact soil temperature and humidity (Bristow 1988, Cox 2009), and soil mulches impact pupal survival in other soil-pupating pest species (Jamieson and Stevens 2006, Renkema et al. 2012). Little is known about the soil conditions necessary for SWD pupation, the depth at which SWD pupate, or the effect of mulches on SWD pupal survival. We aim to collect data on SWD field biology and evaluate the efficacy of environmental manipulation strategies in canopy (Objective 1) and soil habitats (Objective 2).Objective 1. Evaluate the potential for canopy management practices to reduce suitability of in-crop habitat for SWD(1.1) Measure impact of pruning on microclimate(1.2) Determine impact of pruning on SWD egg laying and larval survivalObjective 2. Evaluate SWD use of the soil-interface and the effect of mulches on habitat favorability(2.1) SWD use of soil for pupation(2.2) Impact of mulch on soil microclimate(2.3) Impact of mulch on SWD

Project Methods
Objective 1.Pruning regimes: Three typical canopy density regimes will be examined in groups of at least three plants with untreated plants between each treated group. Treatments will be arranged in a randomized complete block design and replicated 3 times within a planting (replicated at 2 planting sites). Pruning will be done during the late dormant period before new growth begins. Treatments will include low thinning (vigorous canes 6" apart before growth) and high thinning (12" apart). Subsequent thinning will be performed as necessary to maintain the gradient of canopy density.1.1 Measure impact of pruning on microclimate: Canopy density, humidity, and air penetration will be quantified using HOBO Microstation Data Loggers outfitted with photosynthetic light, wind, and relative humidity sensors that are deployed in the center of the canopy throughout the growing season. Four-channel HOBO data loggers will be used to measure air temperature in the lower, middle, and upper portion of the canopy. Thermocouples secured within fruit and the canopy will measure the ambient microclimate and internal fruit temperature. Thermocouples measuring internal fruit temperatures will be moved to fresh fruit weekly.1.2 Determine impact of pruning on SWD egg laying and larval survival: SWD egg laying and larval survivorship in the field will be determined for each microclimate by exposing fruit in the field to SWD within mesh inclusion bags. This ensures that data can be gathered regardless of the natural SWD population level in 2016. Mesh bags (1 gallon paint strainer bags) will be placed over green clusters of fruit to eliminate possible SWD field infestation of fruit prior to color. This system was successfully used for experiments during the 2015 growing season and is an effective way to contain/exclude SWD in raspberries (Hamby et al. unpub.). At least three bags, each containing a cluster of fruit with at least five berries will be placed within the center and the edge of the canopy at each of the predetermined heights where data loggers are deployed. Once fruit ripen, the clusters five mated female and three male D. suzukii (sourced from our laboratory colony) will be released within the bag for 24 hrs, after which all flies will be removed and the bags replaced. Fruit will be collected after 7 days and held at 22°C in the laboratory until adult fly emergence. Emerged adult flies will be counted to determine survival rates. This experiment will be replicated at least two times during the harvest season.Because the previous experiment did not allow females to choose the locations within the canopy for egg laying, field oviposition and survival rates will also be evaluated. Fruit clusters containing at least 5 fruit will be randomly flagged when green (equivalently ripe across the clusters) at the six locations within the canopy previously mentioned. No bags will be placed on these fruit so that natural SWD will be able to infest these fruit. When fruit reach market ripeness, fruit will be harvested and oviposition rates and survivorship will be evaluated using the same laboratory rearing methods described above. This will be repeated at least 2 times during the later part of harvest season to ensure that a high natural SWD population is present.Objective 2.1 SWD use of soil for pupation: To determine the proportion of SWD pupating in fruit versus the soil across larval densities, season, and fruit types, we will use the two blackberry, red raspberry, and blueberry varieties for comparisons between hosts and seasonal phenology at both sites. Clusters of approximately 3-5 caneberries or 15-20 blueberries will be artificially infested in the field using inclusion bags as described above. Fruit will be bagged with mesh inclusion bags when all fruit in the cluster are still green (different times during the season for each fruit and variety). When fruit reach the stage just before commercial ripeness, laboratory reared mated female SWD will be released within the bags for 24 hours at densities of 2, 5, and 10 females with 2, 3, and 5 males, respectively (each replicated at least 3 times). Fruit clusters will be placed within inclusion bags and a funnel placed underneath them leading to a soil container. The soil within the container will be gathered from the plot margins to ensure a similar soil type and moisture as occurs under the fruit. These containers will be held for 2 weeks before fruit and soil are evaluated to locate pupae.2.2 Impact of mulch on soil microclimate: A study will be conducted using 'Joan J' primocane red raspberries at both sites. A standardized weed mat (landscape fabric), black plastic mulch, nursery purchased bark mulch (bagged hardwood mulch rather than landscape debris), and no mulch control will be evaluated. Mulch treatments will be applied to at least 3 consecutive plants and up to a full row of plants with untreated plants used as buffers between the treatments and each treatment will be replicated at least 2 times at each site. After the canes are pruned down during the dormant season and before canes break dormancy, the black plastic mulch that is currently in use will be removed and the new mulch treatments will be placed along the edges of the cane row. This will allow new canes to grow in a 1ft band in the center of the row while the mulch treatment is applied along the edges. In a commercial planting, the mulch treatments would be applied at planting and cover the entire bed. The mulch treatments would also be more applicable for commercial floricane fruiting varieties where the canes do not get mowed down and the mulches wouldn't interfere with mowing. We are using a primocane fruiting variety because the more extreme pruning allows us to more easily apply the mulch to an established planting. Treatments will be arranged in a RCBD within a planting, with each treatment replicated at least 3 times. The impact of mulches on the microclimate will be measured using four channel HOBO data loggers deployed below the plant canopy over the mulch treatment. Measurements will be conducted at a 4" soil depth, at the soil surface, within a fallen berry at the soil surface, and 4" above the soil surface in canopy. Thermocouples within the fallen berries will be moved every week.2.3 Impact of mulch on SWD: To evaluate late larval and pupal survival for mulch treatments, laboratory reared individuals at known densities will be placed within inclusion cages at three positions: (1) on top of the mulch, (2) at the surface of the soil below the mulch, and (3) one inch directly below the soil surface under the mulch. This will be performed under the center plant for each mulch replicate. Two exposure treatments will be included: fully exposed pupae or pupae inside infested fruit [blueberries will be used because some pupation occurs inside blueberry fruit (Author's observation)]. Cages will be left in the field for two days and then returned to 22°C in the laboratory and held until adult emergence to determine survivorship. Laboratory experiments will be conducted to determine whether the pre-pupal larvae are capable of penetrating the mulches prior to pupation and to determine whether adults are capable of emerging when pupae are buried at various depths in sand and field collected soil under mulch. Field infestation will be measured by sampling 15 fruit at commercial ripeness from random positions in the canopy and 15 fruit from the mulch surface at the center plant of each treatment 2 weeks before harvest concludes. Because the distribution of larvae within a fruit sample is rarely measured, fruit will be held 2-3 days after collection and larvae will be counted for each individual fruit using a sugar solution method (Hamby et al. 2014).

Progress 01/19/16 to 06/30/17

Outputs
Target Audience:Maryland fruit and vegetable farmers, University of Maryland research farm personnel, University of Maryland extension staff and faculty, and scientists working with spotted wing drosophila in the North East were reached through our efforts. Changes/Problems:Significant problems were encountere for sub objective (2.1) SWD use of soil for pupation.Greenhouse and climate controlled chamber studies were attempted for this objective. In the greenhouse, temperatures reached >100°F when laboratory flies were bagged on potted blueberry plants, and the flies died before laying eggs. In the climate controlled chamber, the blueberry plants were killed prior to the end of the manipulative studies. Therefore, we were not able to generate meaningful data for this objective. What opportunities for training and professional development has the project provided?One postdoctoral scholar, Christopher M. Taylor, a research technician, Arielle Arsenault-Benoit, and multiple undergraduate students received one-on-one training in experimental design, blueberry and raspberry horticultural practices, IPM, and spotted wing drosophila biology and management. Christopher Taylor and Arielle Arsenault-Benoit have been provided professional development opportunities and experience in Extension presentations, posters, fact sheets, and blogs to disseminate this work. They have also gained experience in collaborative research and management, and opportunities to attend conferences and network with potential employers. How have the results been disseminated to communities of interest?Other extension specialists and researchers were reached via in-service meetings, through a poster at the national spotted wing working group (WERA-1021: Spotted wing drosophila biology, ecology, and management) meeting, and conference presentations. Demonstrations of research plots and techniques during field days enabled stakeholders to see the experiment in person and provide feedback on future iterations of the work. Presentations at winter meetings and extension publications increased stakeholder knowledge and awareness of work to develop alternative management strategies and the future promise of these specific cultural control tactics. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Spotted wing drosophila (SWD) is a devastating invasive insect pest of soft-skinned fruits native to eastern Asia. It was first found in the mainland U.S. in 2008, and is estimated to cause $718 million of crop losses annually in the U.S. Most large-scale farmers now apply broad-spectrum insecticides weekly when fruit are ripe in an attempt to manage SWD. This is not an economically feasible management strategy for smaller scale farmers, and has dramatically impacted the economic and environmental sustainability of soft skinned fruit production. Alternative management strategies are desperately needed. In this project we collected field biology data to better understand SWD distributions and habitat preferences within crops. This data will facilitate downstream development of cultural pest management strategies, which require a sound understanding of pest biology to implement successfully. We also evaluated potential cultural control practices such as canopy management (pruning) and mulches to gather preliminary data on their efficacy and feasibility for use as management tactics. Both the pruning and mulching experiments we conducted indicate that SWD survivorship and infestation can be impacted by these practices. In particular, cultural practices that increase the duration of hot temperatures (>87°F) negatively impact SWD. Additionally, data obtained from this project was used to obtain funding for an expanded research project, with the ultimate goal of developing sustainable and effective alternate management strategies that will lower production costs, and increase marketable yields and profits for fruit farmers while maintaining environmental stewardship. During this project we directly reached 496 stakeholders in the Mid-Atlantic region through our in-person participation in Extension meetings, field days, and conferences. In addition, we produced multiple handouts and Extension publications that reach extended target audiences. Survey responses (149 respondents) indicate that 78% of stakeholders find the SWD information we present to be beneficial for their operations, and 69% of these respondents would share the information with others. Objective 1. Evaluate the potential for canopy management practices to reduce suitability of in-crop habitat for SWD (1.1) Measure impact of pruning on microclimate The pruning experiment was conducted in summer 2016 using 2 year old Joan-J primocane fall bearing red raspberries at two University of Maryland farms: WMREC, Keedysville, MD and WyeREC, Queenstown, MD. Three pruning treatments 1) no pruning, 2) medium pruning, and 3) high pruning were compared. Pruning was performed in mid July after the raspberry plants finished the majority of their vegetative growth. A Leaf Canopy Analyzer was used to quantify differences in foliage and canopy at the center of the treatment block. Temperature and relative humidity loggers were deployed a in the inner and outer portions of the canopy at approximately the same height, and loggers recorded data every 20 minutes for the 12 week harvest season from August to October. Canopy density varied significantly by treatment at WMREC (Treatment F2,4 = 16.7, P = 0.01) but not WyeREC. Temperature and relative humidity logger data was analyzed as the mean hours of stressful climatic conditions (<70%RH, >87°F) over the course of the twelve week harvest season. At WMREC, the site where canopy density varied significantly, a significant effect of treatment was observed (Treatment F2,48 = 8.09, P =0.001) for temperature but not humidity. At WyeREC, a significant treatment by canopy location interaction was observed (Location*Treatment F2,43 = 4.78, P =0.013). (1.2) Determine impact of pruning on SWD egg laying and larval survival Ten fruit from the interior canopy and exterior canopy were sampled for each treatment replicate every week. At WMREC, the site where pruning treatments significantly impacted the canopy, significantly more larvae were found in the no-pruning treatments compared to the mid and high pruning treatments (Treatment F2,149 = 7.82, P =0.001). At WyeREC, there were not significant differences in larval infestation by treatment or canopy location. These preliminary results indicate that changes in the within-crop habitat can impact SWD infestation, with significant differences in infestation observed at the site where canopy and temperature were impacted by the pruning treatments (WMREC). These experiment demonstrated that with further optimization, pruning could be an effective cultural control tactic to add to SWD IPM programs. Therefore, we have increased our knowledge of how this tactic could be incorporated into SWD management systems and critical aspects of canopy manipulation necessary for success. Objective 2. Evaluate SWD use of the soil-interface and the effect of mulches on habitat favorability (2.2) Impact of mulch on soil microclimate The mulching experiment was conducted in summer 2016 using 2 year old Bluecrop blueberry bushes at the abovementioned farms. All six rows were mulched with woodchips sourced from local landscape trimmings (mixed wood types), and three rows were subsequently covered with a black woven plastic weed mat fabric. Temperature loggers were deployed above the mulch (resting on top) and ~1" below the mulch underneath the center plant of each row and logged temperature at 20 minute intervals. At WMREC, the number of hours above 87°F was not impacted by mulch type and significantly more time >87°F above the mulches than below the mulches (Location F1,21 = 15.92, P =0.0007). However, at WyeREC, both mulch type (Treatment F1,21 = 4.55, P =0.0450) and location above or below the mulch (Location F1,21 = 37.49, P <0.0001) impacted the number of hours >87°F. The black plastic weed mat fabric mulch was >87°F longer than the woodchip mulch and this site exhibited a strong difference above and below the mulch. (2.3) Impact of mulch on SWD Because the location of SWD pupation is poorly understood, we evaluated the impact of mulch on two SWD life stages that may be exposed to ground temperatures: infested fruit (larvae within fallen fruit) and exposed pupae (a proxy for larvae leaving fruit to pupate). To do this, laboratory infested blueberries (between 40-50 eggs) werebagged. Concurrently, early-stage pupae were adhered to cards, enclosed in wire mesh cages, and also bagged. Bags of both types were placed either above or below the mulch treatments at each site and left for one week. In addition, three replicates of each type of bag were held a temperature controlled growth chamber as a control. At WMREC, there were no significant differences in pupal survival by treatment or location and no adults emerged from any infested berry bag deployed in the field. At WyeREC, temperatures varied between mulch treatments and locations and there was a significant treatment*location interaction for pupal survival at this site (Treatment*Location F1,18 = 9.88 P= 0.0056). For development within fruit, field deployed infested fruit exhibited 0% survivorship above the mulch in both treatments. Laboratory controls survived well and field deployed fruit exhibited much lower survival for all experiments. These preliminary results indicate that mulches differentially impact the temperature above and below the mulch surface, and that each site's climate also plays a role. Where cooler temperatures were seen significantly better SWD survival was also observed. Therefore, these experiments indicate that increasing duration of hot temperatures that SWD experiences could reduce SWD populations. Further research is necessary before these cultural control methods can be used successfully in the field; however, mulches show promise as a new management tactic for future SWD IPM programs and we have improved our understanding of important features and potential pitfalls for using mulches to manage SWD.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Hamby, K., B. Butler, M. Lewis, and C. Taylor. 2017. Updates on spotted wing drosophila management for diversified small fruit farms. 62nd New Jersey Agricultural Convention and Trade Show 2017 February 7-9, 2017 (~40 people)
• Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Taylor, C., Butler, B., and Hamby, K.A. 2016. Does canopy manipulation impact yield and SWD infestation levels in the outer versus inner canopies of raspberries? 92nd Cumberland-Shenandoah Fruit Workers Conference. Winchester, VA. (~20 people)
• Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Taylor, C.M., Butler, B.R., and Hamby, K.A. 2016. Mulching practices alter the mulch environment and impact Drosophila suzukii larval and pupal survival. WERA1021 Spotted Wing Drosophila Biology, Ecology, and Management, September 29, 2016 (poster)
• Type: Other Status: Published Year Published: 2017 Citation: Hamby, K., B. Butler, M. Lewis, and C. Taylor. 2017. Updates on spotted wing drosophila management for diversified small fruit farms. 62nd New Jersey Agricultural Convention and Trade Show 2017 Proceedings: February 7-9, 2017 p., 87-89. (Extension Publication)
• Type: Other Status: Published Year Published: 2016 Citation: Taylor, C., Butler, B., and K. Hamby. 2016. If you cant take the heat, stay out of the mulch: How mulching practices affect spotted wing drosophila survival in blueberries. University of Maryland Extension Vegetable and Fruit News: October 21, 2016 7(6): 1-3. (Extension Publication)