Gao, Y. G., Extension Specialist and Associate Professor, South Centers, The Ohio State University
Slaughter, M.R., Research Assistant, South Centers, The Ohio State University
Scurlock, D.M., Retired Viticulture Outreach Specialist, The Ohio State University
Worley, C.T., Director and Associate Professor, South Centers, The Ohio State University

ABSTRACT

A comprehensive monitoring study of the spotted wing drosophila (SWD) was initiated at a research and extension center near Piketon, Ohio, where blackberries, blueberries, raspberries, wine grapes and a woodlot of mixed trees and shrubs are present. The PHEROCON© SWD traps with Trece lures and without Trece lures were used in this study. Overall, the PHEROCON© SWD traps with Trece lures were more effective in catching SWDs than those without Trece lures on most trapping dates. Our trap counts suggested that raspberry was the most attractive crop to SWDs among the fruit crops we monitored. However, more than 100 SWDs were caught per trap in the woodlot. Blackberries, blueberries and wine grapes were not as attractive to SWDs as raspberries. Our results on blackberries may have been skewed by the limited amount of fruits on blackberry bushes due to winter injuries. Management of SWDs in the woodlot near the fruit plantings may be a big challenge since insecticides are not labeled for use on the trees and shrubs in the woodland. Growers need to more closely monitor the fruit crops near wooded areas for early detection. They may also need to make insecticide sprays to those fruit plants closer to the woodlot than those that are farther away. SWD trapping and monitoring, though time consuming, may be a good way for extension agents and educators to help growers more effectively manage this new invasive pest.

INTRODUCTION

The spotted wing drosophila (SWD) is a small vinegar fly that has the potential to damage many different fruit crop species (Isaacs et al., 2010). Annual SWD-attributed crop loss estimate in the U.S. is $1,276,992,028 (Burrack, 2015). Economic host crops of the SWD include blackberry, blueberry, cherry, grape, raspberry, strawberry and tomato. 

SWD is a new invasive pest in the United States and was first discovered in several western states in 2008. SWD was first detected east of the Rocky Mountains in Florida, Michigan and the Carolinas in 2010 (Isaacs, et. al., 2010). SWD was first discovered in one Ohio county in 2011, then detected in 11 counties in 2012, and in 37 counties in 2013 (Jasinski and Welty, 2014). Despite the quick spread of the SWD in Ohio, it was still unclear where SWD overwintered and which economic crops are its preferred hosts where multiple fruit crop species are present.

A SWD trapping study was conducted at a research and extension center in Ohio in 2014 using traps baited only with apple cider vinegar and a drop of unscented dish soap (Gao et al., 2015). SWDs were first caught in a blackberry planting, raspberry planting and a woodlot on August 14, 2014. In the wine grape vineyard, the first SWD was caught in grape cultivars “Hibernal” and “Noriet” on September 11, 2011. More SWDs were found in plantings of the four grape cultivars at the research and extension center on September 25 and October 3. Few SWDs were found in plantings of all four grape cultivars on October 23. Additional SWD were trapped near all four cultivars on October 30 where larger numbers of SWDs were found in “Vidal”. Our results were not conclusive enough to show if the darker fruited grape cultivars, such as “Noriet” and “Chambourcin”, were more attractive to SWD (Gao et al., 2015). 

An “improved” PHEROCON^© SWD trap with a Trece lure was introduced in late 2014. Several researchers have conducted SWD monitoring studies with this trap and achieved mixed results (Conklin, 2016). A comprehensive SWD monitoring was conducted in 2015 to determine if the PHEROCON^© trap with Trece lure is more effective that those without Trece lure. Our second objective of this study was to determine which crop SWD would attack first where multiple fruit species, such as blackberries, blueberries, grapes, raspberries, and a woodlot of mixed trees and shrubs are present. Our third objective was to determine which crop(s) were most attractive to SWDs in a site where mixed fruit crops and the woody trees and shrubs are present.

 

MATERIALS AND METHODS

SWD Traps and Lures

The SWD traps used in this study were the 2014 version of the commercial PHEROCON^© SWD trapes (Trécé Inc., Adair, OK, USA). The drowning solution used was apple cider vinegar (ACV) as suggested by the manufacturer’s instructions (Trécé Inc., 2014). Approximately 210 milliliters or one inch depth of ACV was poured to those traps (Figure 1). One drop of unscented dish soap was also added to the drowning solutions. The lures used were Trece “High Specificity Lures” (Trécé Inc., 2014).

Figure 1. Hannah Overly hangs a PHEROCON^© SWD trap with “High Specificity Trece Lures” (Trécé Inc., Adair, OK, USA) in our research and demonstration vineyard. Photo by Ryan Slaughter, The Ohio State University.

 

Trap Types and Number of Traps

• In the blackberry plot, two PHEROCON^© SWD traps, one with Trece “High Specificity Lure,” situated over an apple cider vinegar drowning solution, and one without a lure, were set out. Trapping duration was from May 28 to September 3.   
• In the field raspberry plot and in the high tunnel raspberry plots, two PHEROCON^© SWD traps, one with Trece “High Specificity Lure,” situated over an apple cider vinegar drowning solution, and one without a lure, were set out. Trapping duration was from May 28 to October 15. 
• In the blueberry plot, four PHEROCON^© SWD traps, two with Trece “High Specificity Lure,” situated over an apple cider vinegar drowning solution, and two without lures, were set out. Trapping duration was from May 28 to August 7.
• In the woodlot, four PHEROCON^© SWD traps, two with Trece “High Specificity Lure,” situated over an apple cider vinegar drowning solution, and two without lures, were set out. A set of two traps with and without lure was placed on the east and west side. Trapping duration was from May 28 to October 15.
• In the wine grape plot, only one PHEROCON^© SWD trap with Trece “High Specificity Lure” was set out to give us an early warning for possible insecticide sprays. Trapping duration was from July 31 to October 15.

 

Trap Monitoring and Maintenance Schedule

All of the traps were monitored on the weekly basis. The drowning solutions were replaced weekly while the lures were replaced once a month. All of the drowning solutions were replaced and poured into separate glass jars for subsequent SWD identification and counts.

Replication and Randomization

Completely randomized replications were not used in this study since this trapping study was mainly used to determine when the first SWD sprays were needed. Since action thresholds have not been established for SWD, a conservative approach would be one SWD fly capture on a farm triggering insecticide application of fields, if berries are at a susceptible stage (Isaacs el al., 2012). Hence, there was not much difference between one fly catch and multiple catches. Finally, the SWD monitoring was a very time consuming and costly process, so the number of traps was limited. 

 

RESULTS

In 2015 SWDs were first caught in the field raspberry plot and the woodlot on July 9 (Table 1). SWDs were then caught in our blueberry plot and the wine grape vineyard on August 7. The first SWD was caught in our blackberry plot on August 13. More SWDs were trapped when we used PHEROCON^© SWD traps with a Trece lure than without a Trece lure on most trapping dates. It is interesting to note that 121 SWDs were trapped in one SWD trap in our raspberry plot on October 15 in a PHEROCON^© SWD trap without Trece lure (Table 1). In the woodlot, the total SWD counts in all traps were 107 on September 10 and 221 on September 24, respectively (Table 1). Raspberry was shown to be most susceptible crop to SWD attack. Blackberry is second while blueberry and grapes may be a close third in our study in 2015.     

 

Table 1. Total Number and Dates of SWDs Trapped at OSU South Centers in Piketon, Ohio in 2015.

Trap Location	# Of Traps Per Location	Trapping Dates	Fruit Harvest Dates In 2015	Date of First Catch	Total # of SWDs in the First Catch in All Traps in Each Plot	Total # of SWDs in the Last Week of Trapping	Highest # Recorded In One Trap (Date Trapped)
Blackberry (Field)	2	May 28 - Sep. 3	July 21 – Aug. 20	Aug. 13	3/2	38/2	31 (Sep. 3)
Raspberry (Outside & High Tunnel)	4	May 28 - Oct. 15	July 31 – Sep. 15	Jul. 9	2/4	344/4	121 (Oct. 15)
Vineyard (Wine Grapes)	1	Jul. 31 – Oct. 15	Sep. 28 – Oct. 8	Aug. 7	21/1	1/1	21 (Aug. 7)
Woodlot	4	May 28 – Oct. 15	N/A	Jul. 9	1/4	213/4	221 (Sep. 14)
Blueberry	4	May 28 - Aug. 7	Jun. 23 - Jul. 14	Aug. 7	23/4	23/4	23 (Aug. 7)

 

SWDs were first caught with PHEROCON^© SWD traps with Trece lure on July 9 in the field raspberry plot (Table 2). This was almost a month earlier than the PHEROCON© SWD traps without Trece lure (Table 2). In the high tunnel, first SWDs were caught with PHEROCON^© SWD traps with Trece lure on July 16, which is only a week earlier than the first trapping date with PHEROCON^© SWD traps without Trece lure. Overall, more SWDs were trapped in the Trece lure baited traps than the non-Trece lure baited traps (Table 2) in both field raspberries and high tunnel raspberries. There were several exceptions in August, September and October.

 

Table 2. Total Number and Dates of SWDs Trapped With and Without Trece Lures in high tunnel and field raspberries at OSU South Centers in Piketon, Ohio in 2015. Weekly trap monitoring began 5/28 and the first SWDs were found on 7/9.

Trapping Dates	High Tunnel Raspberry		Field Raspberry
	Trap with Trece Lure	Trap without Trece Lure	Trap with Trece Lure	Trap without Trece Lure
7/9/2015	0	0	2	0
7/16/2015	4	0	0	0
7/23/2015	26	2	12	0
7/30/2015	45	2	13	0
8/7/2015	12	17	42	3
8/13/2015	60	16	0	1
8/20/2015	62	6	9	4
8/27/2015	22	0	17	2
9/3/2015	16	12	46	4
9/10/2015	63	59	6	36
9/24/2015	60	99	32	26
10/1/2015	23	8	12	22
10/15/2015	59	75	89	121
Grand Total	452	296	280	219

 

SWDs were caught in both PHEROCON^© SWD traps with and without Trece lures on the east side of the woodlot on July 16 (Table 3). No early detection was achieved with PHEROCON^© SWD traps with Trece lure on the east side (Table 2). More SWDs were caught among 8 out of 12 trapping dates with PHEROCON^© SWD traps with Trece lures on the east side of the wooded plot. On the west side of the wooded plot, one SWD was caught on July 9 in the PHEROCON^© SWD traps with Trece lure. This catch is about two weeks earlier than the PHEROCON^© SWD traps without Trece lure. More SWDs were trapped in PHEROCON© SWD traps with Trece lure during 12 out of 13 weeks of SWD trapping. Overall, more SWDs were caught on the west side of the wooded plot in comparison to the east side. 

 

Table 3. Total Numbers and Dates of SWDs Trapped with PHEROCON^© SWD traps with and without Trece Lures on the East and the West Side of the Wooded Plot at OSU South Centers in Piketon, Ohio in 2015. Weekly trap monitoring began 5/28 and the first SWDs were found on 7/9.

Trapping Dates	PHEROCON© SWD Traps With Trece Lure on the East Side of the Woodlot	PHEROCON© SWD Traps Without Trece Lure on the East Side of the Woodlot	PHEROCON© SWD Traps With Trece Lure on the West Side of the Woodlot	PHEROCON© SWD Traps Without Trece Lure on the West Side of the Woodlot
7/9/2015	0	0	1	0
7/16/2015	2	1	3	0
7/23/2015	5	1	3	1
7/30/2015	1	1	6	0
8/7/2015	5	10	41	4
8/13/2015	8	19	2	3
8/20/2015	6	0	6	0
8/27/2015	9	4	82	0
9/3/2015	8	4	36	7
9/10/2015	107	18	62	34
9/24/2015	17	37	221	29
10/1/2015	25	7	33	20
10/15/2015	90	19	89	15
Grand Total	283	121	585	113

 

In the open field blackberry plot, SWDs were first caught in PHEROCON^© SWD traps with Trece lure (Table 4). This is one week earlier than the first SWD catch in PHEROCON^© SWD traps without Trece lures (Table 4). Thirty eight SWDs were caught in the PHEROCON^© SWD traps with Trece lures in comparison to 9 in those PHEROCON^© SWD traps without Trece lures (Table 4). It should be noted that there was only a limited amount of fruit in our blackberry plot due to the cold injuries to the floricanes in 2015. 

 

Table 4. Total Numbers and Dates of SWDs Trapped With and Without Trece Lures in the Blackberry Plot at OSU South Centers in Piketon, Ohio in 2015.

Date	PHEROCON© SWD Traps with Trece Lure	PHEROCON© SWD Traps without Trece Lure
8/13/2015	3	0
8/20/2015	3	1
8/27/2015	1	1
9/3/2015	31	7
Grand Total	38	9

 

Very few SWDs were caught in the blueberry plot even though there were abundant blueberry fruits in 2015. Traps with and without lures, placed on the east and west side of the blueberry plot were monitored weekly starting June 4. SWDs were only caught in one PHEROCON^© SWD trap with Trece lure on the west side of the blueberry planting on August 27, 2015 (23 SWDs). No SWDs were caught in other traps throughout the trapping dates in all other traps.

 

CONCLUSIONS

• Raspberries in both the open field and the high tunnel were most attractive to SWDs at our research center based on the early SWD catches and greater total numbers of catches in 2015. 
• The first SWD catch was also recorded at the woodlot in 2015 and suggests that some fruits on woody trees and shrubs may serve as good hosts of SWDs. 
• Blackberries were quite attractive to SWDs even though very limited amount of fruits were present in 2015.
• Blueberries were not as attractive to SWDs as raspberries even though fruit load on our blueberry bushes was quite high.
• PHEROCON^© SWD traps with Trece lures were generally more effective in detecting and trapping SWDs than those PHEROCON^© SWD traps without Trece lures on most trapping dates.
• Placement of the traps may be important. At this site, the west side of the row and plots seems to be the more effective side than the east side in terms of catching SWDs. 
• Monitoring of SWDs in nearby (probably within 500 feet) woodlots should be a major part of the overall SWD management program in fruit crops.   

 

DISCUSSION

There is currently no recommended threshold for SWD; one fly is used to guide spray applications (Isaacs el al., 2012). Since early detection of the first fly catch is very important for the management of SWDs, this study suggests that the PHEROCON^© SWD traps with Trece lures is an improvement over those PHEROCON^© SWD without Trece lures. It is worth noting that this trend did not hold true on all of our trapping dates. We do not know if this inconsistency is due to the limitation of the lack of replication or the diminishing effect of the Trece lure after being placed in the field for three to four weeks. Other SWD traps have been shown to be more effective than PHEROCON© SWD traps (Conklin, 2016). Furthermore, we wonder if changing the Trece lures after one month was the best practice, since Trece lures are supposed to last 4-6 weeks. Trece lures may not be effective one month after they have been placed in the field. A replicated study of all available SWD traps on a larger scale could address these questions, if sufficient funding were available. 

Labeled insecticides and control strategies are available in the 2017 Midwest Fruit Pest Management Guide (Bordelon et al., 2017). In general, soft fruited crops, such as blackberries and raspberries, are quite attractive to SWDs (Conklin, 2016; University of Minnesota, 2016). Our results also showed that raspberries are highly attractive to SWDs.

It is likely that significant numbers of SWDs overwinter in the woodlot. Our results showed significant SWD catches in the woodlot of mixed plant species. A statewide trapping study in Minnesota showed large numbers of SWD catches in the woodlots with mixed host plant species (University of Minnesota, 2016). The woodlot used in our study is approximately 450 feet away from the blackberry planting. Since insecticides are not labeled for trees and shrubs in the woodlot, our recommendation is that fruit growers may need to place SWD traps on the edges of the woods for early detection. Fruit crops closer to the woodlot may need to be sprayed first and more regularly. Removing wild host plants, such as wild grape, pokeberry, honeysuckle, nightshade, dogwood, spicebush, autumn olive, raspberry, and blackberry, near crop fields has been suggested as a potential strategy (Isaacs et al., 2014). It has also been mentioned that the presence of honeysuckle near crop fields was a predictor of more activity from SWD (Isaacs et al., 2014).

SWDs will continue to be a major challenge to fruit growers in many states. Since this was a one-year study, extension professionals and growers are encouraged to work with their state entomologists to obtain the most up-to-date information on SWD. The actual impact of SWD has been measured through a nationwide grower survey (for more information: https://survey.ncsu.edu/swd/). Extension agents and educators can learn how to properly trap and identify SWDs so that they can help growers manage this serious pest more effectively and build a stronger clientele base in their own perspective region.

 

LITERATURE CITED

Bordelon, B., Beckerman, J., Ward Gautier, N , and Strang, J. (2017). Midwest Fruit Pest Management Guide.  Retrieved on March 3, 2017 from https://ag.purdue.edu/hla/hort/pages/sfg_sprayguide.aspx

Burrack, H. (2015). SWD Impacts 2014. North Carolina State University. Retrieved on March 3, 2017 from https://swd.ces.ncsu.edu/swd-impacts-2014/

Conklin, M. (2016).  Lure Test Results for SWD Traps. Retrieved on May, 17, 2017 from https://blogs.cornell.edu/swd1/2016/05/03/lure-test-results-for-swd-traps/

Gao, Y.G., Slaughter, M.R., Daniels, M.C., and Bergefurd, B.R. (2015). A Spotted Wing Drosophila Trapping Study in the Small Fruit and Grapes Plots and a Woodlot at Piketon, Ohio. [Abstract]. HortScience. 9 ed. Vol. 50. Alexandria: American Society for Horticultural Science. (Sep 2015): S341. Retrieved on March 1, 2017 from http://hortsci.ashspublications.org/content/50/9/suppl/DC1

Isaacs, R., Hahn, N. ,Tritten, B., and Garcia C. (2010). Spotted Wing Drosophila - A new invasive pest of Michigan fruit crops. MSU Extension Bulletin E-3140. Retrieved from http://www.ipm.msu.edu/uploads/files/SWD/E-3140.pdf

Isaacs, R., Tritten, B., Van Timmeren, S., Wise, J., Garcia-Salazar, C., and Longstroth, M. (2012). Spotted Wing Drosophila Management Recommendations for Michigan Raspberry and Blackberry Growers. Retrieved from MSU IPM’s website: http://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdf

Isaacs, R., Wise, J., Garcia-Salazar, C., and Longstroth, M. (2014). SWD Management Recommendations for Michigan Blueberry. Retrieved on May 17, 2017 from  http://www.ipm.msu.edu/uploads/files/SWD/SWDManagementforMichiganBlueberries_-June212014.pdf  

Jasinski, J. and Welty, C. (2014). Establishing a Rapid Reaction Monitoring Team for Invasive Species. The Ohio State University IPM Program. Retrieved on March 1, 2017 from https://u.osu.edu/pestmanagement/files/2014/12/SWD-and-BMSB-2013-Ohio-report-ytdzrh.pdf  

Trécé Inc. (2014). PHEROCON SWD Trap Assembly Instructions. Retrieved on May 17, 2017 from http://www.trece.com/PDF/Pherocon_SWD_trap.pdf

Trécé Inc. (2017). The NEW & IMPROVED Monitoring System for Spotted Wing Drosophila, Drosophila suzukii.  Retrieved on May 17, 2017 from http://www.trece.com/PDF/Pherocon_SWD_flyer.pdf   

University of Minnesota. (2016).  2016 SWD Trapping Network. Retrieved on May 17, 2017 from https://www.fruitedge.umn.edu/swdtrap

 

ACKNOWLEDGEMENTS

We would like to thank our former student interns, Michael Daniels, Dannah Diedrick, and Hannah Overly, for their assistance with this project. Our sincere appreciation also goes to the Ohio Grape Industries Program and the Ohio Department of Agriculture for their financial support.

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