Spotted Wing Drosophila: Year 1 in Eastern Washington Elizabeth H. Beers, Doug Walsh, Tim Smith

Spotted Wing Drosophila: Year 1 in Eastern Washington Elizabeth H. Beers, Doug Walsh, Tim Smith Spotted wing drosophila (SWD) was found for the first time in eastern Washington in the summer of 21. This pest was first detected in the continental US in 28 (in California); in 29, further trapping revealed the presence of this pest in the I-5 corridor in Oregon and western Washington, the Columbia Gorge, and a late season find in British Columbia. By January 21, the information on distribution had been widely reported, and eastern Washington growers were alerted to the possibility that this pest might also invade our area. Tempering this threat was information on the biology of this pest, which indicated that its geographic range would be limited by climate. This species was known to be both cold- and heat-sensitive, and thus would only become established in temperate areas (mild winters and summers). Bioclimatic modeling indicated that 1) all of the known occurrences were in the predicted high risk areas (primarily the coastal areas of the Pacific states); and 2) the fruit production area of eastern Washington were classed as marginal or unsuitable for establishment of this pest. Thus, while were on alert for the presence of this pest, we didn t really expect to find it (Fig. 1). Eastern Washington (enlarged) Fig. 1. Climatic suitability for establishment of spotted wing drosophila, M. Damus, 29. All this changed on 28 June, when the first trap sample containing SWD was brought to the Tree Fruit Research and Extension Center in Wenatchee. The sample was from a commercial cherry orchard in the Mattawa area, well north of the high risk area next to the Oregon border. That -1-

find was quickly followed by another one from the Orondo area, even farther north. It was at this point we realized that a comprehensive trapping program was needed in eastern Washington. Traps were deployed in the next two weeks in most of the fruit growing regions of eastern Washington. From the initial 57 traps deployed in late February, the trapping effort increased rapidly through July and early August, with nearly 5 traps being checked per week at the peak. Most of the traps were baited with apple cider vinegar (ACV), but wine-based and yeast-based baits were also tested on a limited scale. Traps were deployed in the known host crops grown in eastern Washington, with the highest numbers of total samples taken from sweet cherry and grape, with some traps also deployed in peach/nectarine, plum/pluot, apricot, blueberry, raspberry/blackberry (cultivated and feral), apple, pear and strawberry. The majority was placed in commercial operations, both conventional and organic; but a few were placed near packing houses and in backyard trees. A total of 6,941 samples were check from March through December 1 of 21, for a total capture of 6,381 adult SWD. Most traps were checked weekly during that period, but a handful were brought in only once to confirm a suspected find. Two WSU entomologists had SWD trapping programs 21, Dr. Doug Walsh of IAREC in Prosser, and myself (TFREC Wenatchee). All of the Walsh traps were collected and counted by WSU employees, while the Beers trapping program was a collaboration with eastern Washington fieldmen. The fieldmen did the trap collection/replacement for the majority of the traps, which were then shipped to (or dropped off at) the TFREC. The trap contents were sorted and counted by WSU personnel, and the traps rinsed and returned to their various programs. This method required three physical traps for each location: one in the orchard, one with the fieldmen, and one being processed at the TFREC. Deli cup trap Contech trap Nalgene bottle Fig. 2. Trap types used to catch SWD, eastern Washington, 21. Three different trap designs were used: 1) the deli cup; 2) the Contech; and 3) a Nalgene bottle (Fig. 2). The deli cup was a home-made trap consisting of a one-quart clear plastic cup with a -2-

snap-cap, with holes punched in the sides for a wire hanger and points of entry for the flies (these points also allowed diffusion of the bait scent). The Nalgene bottle traps were also home-made from 2 ml bottles with a screw cap. The hanger was incorporated into the lid, and holes punched in the upper sides for the point of entry. The Contech trap was the only commercially made trap (Contech, Inc.; www.contech-inc.com). It was also a screw-cap type, but with a much smaller volume (about a 2 ml capacity). The hanger was also attached by punching a hole in the lid, and either inserting a screw eye to attach a wire hanger, or tying a more flexible cord and knotting it on the underside of the lid. The Contech had only two entry holes, connected by a straw with and elongate aperture in the underside. The Nalgene bottle and Contech were relatively rigid and easy to handle; the deli cups were much thinner plastic, and more prone to breakage. The screw caps provided a more secure seal for the container than the snap-cap style lid. The deli cups and Nalgene bottles required a second container to remove the bait in the field and transport it to the lab; with the Contech trap, the lid remained attached to the tree, and the entire trap body was removed and replaced. Because of the ease of handling, the cooperating fieldmen used the Contech trap exclusively; the Beers program traps collected by WSU personnel were a mix of deli and Contech; and all Walsh program traps were the custom-made Nalgene bottle. A limited comparison of the deli cup and Contech traps was made (Fig. 3). Paired traps were set out in the Orondo-Wenatchee area with the one of each trap type placed about 15 feet apart down a tree row. Both were baited with ACV. A total of 14 pairs were deployed in July, and were checked from 12 July through 2 October. The resulting trap catch was compared using a paired t-test of male, female, and total flies (n=187 obs). In all of those categories, the deli cup caught more flies than the Contech trap by 41% (males) 32% (females), similar to the percentage of the total adult numbers (38%). It is not entirely surprising that the deli cup caught more than the Contech given the deli cup s larger size (1, ml vs 2 SWD/trap/week Males Females Total ml) and larger bait load (1 ml vs 4 ml). However, feedback from the employees who handled both types of traps indicated that the Contech was much easier to handle; the smaller size, rigid sides, and screw cap made it much less prone to spills. The traps could be charged with bait in the lab rather than in the field, and the transporting the entire trap meant that the contents didn t have to be poured out in the field. An additional consideration for the Beers program was that the many of the traps were shipped via a local carrier, and the Contech was much better suited to shipping. While the majority of the traps were baited with about 1 inch of ACV in the bottom of the trap, a red wine-based bait, aka Superbait, was also tested. This bait was composed of a mixture of water, red wine, ACV, molasses, and a wetting agent. Contech traps with the two baits were 12 1 8 6 4 2 Deli Contech +41% +32% +38% Fig. 3. SWD trap catch in deli cup vs Contech traps, 21. -3-

deployed in the same block, with 23 replicates checked from 11 July through 24 October (n=93 obs; not all pairs were checked each week). The Superbait bait caught 36% more males, 52% more females, and 43% more total SWD than the ACV traps (Fig. 4). Thus, while the advantage of Superbait was clear in terms of superior trap catch, it was more difficult and expensive use. Multiple components increase the cost and preparation time, and the bait was cloudy and tended SWD/trap/week 25 2 15 1 5 ACV vs SuperBait (max catch=444) ACV SuperBait ns Males Females Total Fig. 4. Apple cider vinegar (ACV) versus Superbait, eastern Washington, 21. b a ns to form a coating of slime around the specimens, which required additional handling time in the lab. After the first catches occurred in June, the populations remained relatively low, with most traps having -3 SWD (Fig. 5). By the first week in August, only about 1% of the samples were positive for SWD, and the pertrap average was.18 SWD/trap (n=286). The first big uptick started August 15, with a first peak of catch about the first of September. The other major change during that period is the percentage of positive traps went from 1 to 6%, another indicator of population expansion. Averages stayed at 5-9 SWD/trap/week during September, then fluctuated between 2-4/trap/week during October and early November. Trap catch was shut down by a cold snap that occurred the nights of 22-24 November (as low as -4 F in Wenatchee), and the majority of the traps were removed from the field. Avg. SWD/trap/week 5 4 3 2 1 % Positive Traps Avg SWD/trap/week Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 5. Seasonal trap catches of SWD in eastern Washington, 21. One interesting case was that of four traps in an isolated cherry orchard near Royal City, WA. Traps were not placed in this orchard until the second week in August, well after the fruit was SWD/trap/week 25 2 15 1 5-4- Trap #1 Trap #2 Trap #3 Trap #4 1 % Positive Traps Jun Jul Aug Sep Oct Nov Dec 2 Fig. 6. Trap catches of SWD in a Royal City cherry orchard (4 traps), 21. 8 6 4

harvested in early July. The traps caught nothing for 1-2 weeks, then a few flies were caught; the last week of September, a 1-fold increase in trap catch occurred, followed by a 28-fold increase the following week (early October) (Fig. 6). The high catches were sustained through October, and reached their highest level in the first week of November, with a record 2,25 flies caught in the easternmost trap (6,539 total for the four traps). There was a gradient in the trap catch from west to east (low to high) that was consistent throughout most of this high catch period. I spent an afternoon with the fieldman searching the environs of this orchard for a source of the SWD, but failed to turn up any likely possibilities. The orchard was fairly isolated (for eastern Washington); there was one cherry orchard a few miles to the west, but the lowest trap catches were on that border. The orchard was surrounded by row crops, sagebrush steppe, and some grassy areas, but visible fruit hosts were lacking. This puzzling example is a reminder that we have a great deal to learn about the ecology of SWD in our area. The information on differences in trap catch among crops (Fig. 7) should be interpreted with caution. The active space of the traps is not known, and until we have a better understanding of this, these are just associations. That said, there do appear to be some interesting trends. The highest average trap catch (all season) was in cherries (17.6/trap/week), with over 3, samples. In stark contrast, the average for traps place in grapes was.74 (1,554 samples). Relatively high averages were found in the other stone fruits: apricot 9.95, peach/nectarine, 8.17; plum/pluot 2.59. There were also higher averages from apple (1.18) and pear (3.33); these are not known to be preharvest hosts, but may have been postharvest hosts. The number of traps in these hosts was very small, and on the same farms where the cherry traps were placed. More surprising was the low catch in blueberry (.71), strawberry (.67) and to a lesser extent, raspberry/blackberry (2.31). These are all known hosts, and considered to be medium to high risk for attack by SWD. Only one SWD was captured in a trap placed near a packinghouse. It should be emphasized that trap catch and risk are by no means the same thing. Strawberry 38 Raspberry/Blackberry Plum/Pluot 1,15 46 Pear 15 Peach/Nectarine 444 Packinghouse Grape Cherry Blueberry Apricot Apple 5 1 15 2 Average SWD/trap (seasonal) n samples total 26 1,554 3,16 513 29 65 Yakima Wenatchee WallaWalla TriCities Tonasket Royal City Rattlesnake Quincy Prosser Othello Orondo Moses Lake Mattawa Chelan/Manson Brewster n samples 14 254 5 1,16 62 82 57 483 2,417 35 1,487 24 643 99 119 Fig. 7. Average SWD trap catches by crop, eastern Washington, 21. 5 2 25 Average SWD/trap (seasonal) Fig. 8. Average SWD trap catches by region, eastern Washington, 21. Regional differences should also be interpreted with caution until we know if they are associated with differences in threat to a crop (Fig. 8). The highest average trap catch was registered in the -5-

Royal City area (26 SWD/trap/week), but as noted previously, much of that was dictated by low numbers of trap sites and the extraordinarily high catches in one orchard. The next highest area on average was Moses Lake, however, this was a single orchard, and cannot be considered representative for the region. Orondo and Wenatchee had a large number Fig. 9. Map of trap locations and seasonal total catch in SWD traps in eastern Washington, 21. White= no catch; blue, 1-1; green, 11-5; yellow, 51-2; orange, 2-5; red, >5. (Images ex Google Earth). -6-

of traps deployed, and the consistently high catches in these areas are likely representative of these regions. Brewster, Chelan/Manson, Tonasket, Prosser and the Tri-Cities all had moderate trap catches, even though the latter two areas trapped very intensively. Yakima and the region below Union Gap (Wapato, Zillah, and Sunnyside) had some of the lowest averages, although these areas were not trapped as intensively. Overall, the seasonal trap catches throughout the region give two clear indications. First, the coverage of the state s fruit growing regions with traps was fairly complete, with traps deployed form the Canadian border to the north to the Oregon border to the south (Fig. 9). The second indication is that most of the negative trap catches were in the lower Yakima Valley, while much of the higher trap catches were north of I-9. A second point that needs emphasis is that we have only one year s data for these regional differences, and we will not know if this trend will persist until we have several more years experience under our belt. Stated otherwise, just because you had low pressure in 21 doesn t mean you ll have low pressure in the coming years. Many of you are aware that a large federal grant was funded in 21 to work on SWD. This grant is lead by Dr. Vaughn Walton of Oregon State University, in cooperation with scientists from the USDA, University of California, California Farm Advisors, and Washington State University. The scope covers berries and tree fruits, with areas of study to include genomics, ecology, phenology, host preferences, monitoring, degree day modeling, biological control, chemical control, resistance, sanitation, economic impact, and outreach. This $5.8 million dollar grant will provide the resources to give producers the basic information they need to control this pest. Because California has had this pest several years at this point, they have had time to develop some chemical control information. Most of the information we have at this point comes from laboratory bioassays or field-lab bioassays, where field-grown trees are sprayed with various pesticides, and leaves or fruit brought in to the laboratory and exposed to lab-reared flies. Dr. Robert van Steenwyk (University of California Berkeley) has conducted an extensive series of bioassays with SWD on treated cherry leaves. His findings indicate there is significant activity in four classes of pesticides (organophosphates, pyrethroids, spinosyns, and neonicotinoids) although there are some differences between products within a class. The organophosphates Malathion and Diazinon appear to be quite toxic to SWD adults. Of the pyretrhoids, Danitol (fenpropathrin) was the most toxic, while Pounce (permethrin), Baythroid, (cyfluthrin) Mustang (zeta-cypermethrin), and Warrior (lambda-cyhalothrin) were similar but less toxic than Danitol. Delegate (spinetoram) and Entrust (spinosad) were both very effective. Of the neonicotinoids, Provado (imidacloprid) was moderately effective, while Assail (acetamiprid) and Actara (thiamethoxam) had little activity. Only one carbamate (carbaryl) was tested, and it was not found to be very effective. The net result is that we have an array of tools to use in our orchards in 211, and can rotate them for resistance management, and time them to stay within preharvest intervals. A replicated field trial by Dr. van Steenwyk also provides some field verification of the lab bioassays. He tested 1, 2, 3, and 4-spray programs, with all sprays having a preharvest Malathion, and adding sprays earlier in the season (Danitol, Mustang, and Diazinon). This test indicated that the single Malathion spray preharvest did not provide control, but all other -7-

programs did. He also concluded that the earliest spray probably added little to overall efficacy, and that 2-3 sprays would provide sufficient control. He also recommended that applications begin when cherries first begin to take on pink color; sprays prior to that did not add protection. However, it should be remembered that SWD overwinters successfully in California s mild winter climate, and they had a peak of spring emergence in early May; eastern Washington will likely have a very different pattern. While many questions still remain to be answered concerning this new invasive pest, we have enough basic knowledge on distribution, population trends, host susceptibility and pesticide efficacy to protect our crops in 211. -8-