Developing an integrated pest management program for a newly introduced pest in Florida blueberries: the spotted wing drosophila, Drosophila suzukii

Developing an integrated pest management program for a newly introduced pest in Florida blueberries: the spotted wing drosophila, Drosophila suzukii

Summary

A survey study conducted in in blueberries 9 Florida counties showed that spotted wing drosophila is present in 8 major blueberry-producing counties. We conducted a trapping study that showed the basic plastic cup trap proved an effective trap for SWD when baited with apple cider vinegar. Bait evaluations in year 2 will help determine the most attractive bait to use in SWD traps. Oviposition no-choice tests show Southern Highbush species appears a more viable than Rabbiteye. Although blue berries are most susceptible to SWD oviposition, we show that green and pink berries are also at risk and recommend setting traps as berries change from green to pink. Pesticide evaluations for SWD suggested that Danitol® at both tested rates were as effective as industry standards.

Objectives/Performance Targets

Obj. 1: To survey SWD in various blueberry growing regions and counties throughout Florida
Obj. 2: To develop an effective monitoring system for SWD
a) To determine the most attractive bait to SWD
b) To determine the most effective trap design for capturing SWD
Obj. 3: To evaluate female SWD oviposition behavior
a) To determine viability of the most grown blueberry species in Florida, Rabbiteye and Southern Highbush, for larval development
b) To determine susceptibility of different berry maturity stages to SWD oviposition
Obj. 4: To identify reduced-risk insecticidal tools to control populations of SWD

Accomplishments/Milestones

The survey study was conducted during year 1 on 15 farms in 9 Florida counties. Traps were made with 0.95 L clear plastic cups with lids with 8 to 10-1/4 inch holes along the sides of the cup. Traps were secured to the middle of blueberry bushes with twist-ties. Each trap was baited with 150 ml of apple cider vinegar (ACV). Each location had between 4 and 7 traps placed along the perimeter of the blueberry field and in the center. Traps were collected weekly for the duration of blueberry season until harvest was completed. Number of weeks at each location varied based on the length of the season. Male and female SWD were identified and counted at the UF Small Fruit and Vegetable IPM Laboratory in Gainesville, Florida.

The average number of SWD per trap was calculated for each county. We found that SWD was present in all counties except for the southernmost county of DeSoto. We believe this is likely a result of the onset of higher temperatures earlier in the season which helped to prevent the outbreak of SWD in the southernmost parts of the state (Fig. 1). We also found a general trend showing more female SWD than males in all counties, with four counties showing significant differences (P ? 0.05, Fig. 2). The results lead us to ask whether the ACV is more attractive to females. We will attempt to answer the above question by testing the attractiveness of different baits in Objective 2 during year two of the study. Based on the results of the trap study, which I will discuss in Objective 2b, we will be changing the standard trap design to a basic cup design with the addition of detergent to the ACV for the survey study next year.

Objective 2a: Bait Study
The bait study will be conducted this year. First we will run lab bioassays using a y-tube olfactometer and then carry out a field study.

Objective 2b: Trap Study
The trapping study was conducted during year one at 2 farm locations. Each experiment had 4 replicates. Five different trap designs were evaluated: 4 modifications of the plastic cup design described above and a standard yellow sticky card control (Fig. 3). Two of the cup treatments had a yellow visual stimulus placed around the rim of the cup, one of which had detergent added to the ACV. The last two cup treatments included one with a small yellow sticky card (7.6 x 7.6 cm) hanging inside and a standard transparent cup. Traps were serviced weekly for 11 weeks during experiment 1 and 5 weeks during experiment 2. Experiment 1 was extended due to low SWD populations. Male and female SWD were identified and counted at the UF Small Fruit and Vegetable IPM Laboratory in Gainesville, Florida.

Both experiments showed similar results of average SWD captured per treatment (Fig. 4). The yellow sticky card (control) was ineffective at capturing SWD. In experiment 1, the cup trap with the yellow sticky card inside captured significantly fewer SWD than the other cup treatments. There were no other differences amongst the cup treatments and all captured significantly greater numbers than the control. Our results suggest that neither the addition of the yellow visual stimulus nor yellow sticky card had an effect on the capture of SWD in the field. The cup modified with the yellow visual stimulus and the detergent seemed to capture higher numbers of SWD although the differences were not significant. Therefore, we will be using the basic cup design with the addition of detergent as the standard trap for the survey study next year.

Both experiments showed similar results of average male and female SWD captured per treatment (Fig. 5). There were generally greater numbers of females in all treatments and significantly more in the unmodified cup trap and the cup trap with the yellow visual stimulus. Again, we ask whether the ACV is more attractive to female SWD.

Objective 3a: Species Viability Study
During year one, we conducted a laboratory no-choice bioassay to look at the viability of two common blueberry species, Southern Highbush and Rabbiteye, for SWD larval development. Two berries were exposed to 10 females for 96 hours (16 replicates). After 14 days, adult emergence was counted daily for 1 week. We found that Southern Highbush appeared to be more viable as a host than Rabbiteye (Fig. 6). We will repeat this experiment in year two. We will also conduct a choice bioassay to determine the susceptibility of each species to SWD oviposition.

Objective 3b: Ripeness Stage Study
We conducted a laboratory choice bioassay to examine the susceptibility of different ripeness stages of Southern Highbush blueberry. Treatments were green, green-pink, pink, pink-blue, and blue. Two branches were placed in each bioassay chamber (28 replicates) and 10 female flies were introduced for 72 hours. Females were observed for 5 minutes daily, ovipositing females counted and berry color noted. Female was considered as ovipositing when the ovipositor was inserted into the skin of the berry. We found that 78 percent of females oviposited on blue berries, 17 percent on green, 5 percent on pink, and none on pink-blue or green pink (Fig. 7). Female SWD was 4.7 times more likely to oviposit on blue than green berries.

The experiment was conducted in two phases between April 9 and 24, 2012. The experimental design was a randomized complete block with 7 treatments and 4 replicates. Treatments consisted of 3 conventional pesticides, Danitol® at 10.333 oz/acre (Dan10.3, Fenpropathrin, Valent Corp., Walnut Creek, CA), Danitol® at 16 oz/acre (Dan16), and Mustang® at 4 oz/acre (Mus4, zeta-cypermethrin, FMC, North Carolina), 3 reduced-risk pesticides, Belay® at 4 oz/acre (Bel4, Clothianidin, Valent Corp., Walnut Creek, CA), Belay® at 6 oz/acre (Bel6), and Delegate® at 6 oz/acre (Del6, Spinetoram, Dow AgroSciences, Indianapolis, IN), and a water treated control (Cont). Mustang Max® and Delegate® treatments were added to provide a comparison of all treatments to industry standards. One day after application (DAA), two branches were selected from blueberry varieties and transported back to the University of Florida, Small Fruit and Vegetable laboratory in Gainesville. One branch from each variety was placed into a bioassay (treatment) chamber for males and the other two branches into a chamber for females.

Adult activity measurements began 24 hours after the flies were introduced into the bioassay containers. Data were taken by picking up the container and gently tapping the sides to elicit an activity response from the flies. Fly activity was measured on a scale of 0 to 3, using methods described in Liburd et al. (2003). A score of 3 indicated unaltered fly activity (fly in its natural state). A score of 2 indicated decreased responsiveness to tapping. A score of 1 indicated responsiveness to tapping and a general inverted, twitching appearance. Fly death was designated a score of 0. Containers were observed for 5 minutes to determine mortality. Data were collected as number of flies in each category (0 through 3). The values were then weighted based on their categorical number and averaged by the number of responding flies in each container (some flies died due to berry drop).

Results indicate that Danitol® at 10.3 and 16 oz per acre are just as effective as industry standards (Mustang Max® and Delegate®) at reducing female SWD activity (Table 1). There were no differences in the SWD activity between the 10 and 16 oz rates per acre. The findings indicate that both rates of Danitol® were more effective at reducing male activity than Mustang® (4 oz per acre) after 1 d and Delegate® (6 oz per acre) after 3 d (Table 2). Belay® at 4 and 6 oz per acre were not effective in suppressing male and female adult activity throughout 14-day study. This study will be repeated in year two with additional reduced-risk pesticides.

• Mean SWD captured per trap in each county
• Mean male and female SWD captured per trap for experiments 1 and 2
• Percent SWD ovipositing on different ripeness stages
• Activity response of female SWD
• Activity response of male SWD
• Mean emerged SWD per berry
• Mean male and female SWD captured per trap in each county
• Trap treatments
• Mean SWD captured per treatment for experiments 1 and 2

Impacts and Contributions/Outcomes

Identifying appropriate traps and baits will allow us and the growers to detect the first appearance of SWD in fields and locate low populations that will guide management action. Moreover, growers will be able to focus their control activities in areas that have high populations of SWD. Our recommendation to blueberry growers is to use the basic cup trap for monitoring for SWD in their fields, based on the results of our trapping study in year one. Our bait research scheduled for year two aims to identify a more attractive and specific bait for capturing SWD in the field. Furthermore, identifying the susceptible stage where berries are more likely to be attacked by the adult fly will allow us to improve timing of reduced-risk pesticides. Previous recommendations were to begin monitoring for SWD as berries became ripe. However, the results of our oviposition study show that monitoring should begin well before that time. We recommend setting traps as berries begin to change from green to pink. Finally, identifying reduced-risk tools that are compatible with beneficial insects will improve control of SWD. The results of our efficacy study show that Danitol® is an effective tool for controlling SWD, even at the lower application rate. Since Danitol® has a preharvest interval (PHI) of 3 days it can be more effectively used at the beginning of the season before peak harvest and leave pesticides with low PHI, such as Malathion, for use during peak harvest. Our continued efficacy research aims to identify additional reduced rick pesticides to add to the growers’ chemical control toolbox.

Collaborators: