Discovery of Spotted- wing Drosophila in the United States

Spotted wing drosophila (Drosophila suzukii (Matsumura), Diptera: Drosophilidae) is an invasive pest recently introduced into Florida that could affect berry production including strawberry, blueberry, blackberry, raspberry and other thin-skinned fruit. In August 2009, spotted wing drosophila was discovered in the northeast corner of Hillsborough County, after having been known in California since 2008 and in Washington since earlier in 2009. As of June 2011 it had spread to several other states and 26 Florida counties. The highest numbers in Florida have been found in Hillsborough, Dade, Palm Beach, and Broward counties.

Biology of Spotted-wing Drosophila

This fly, originating in the Orient, resembles the common Drosophila spp. flies that accumulate on over-ripe bananas, flats of strawberries left without refrigeration, old fallen citrus, discarded watermelon rinds, and other fruit beginning to decompose. Both flies are small (1/8 inch or 2-3 mm), have prominent red eyes and, indeed, are closely related. However, wing tips of male spotted wing drosophila incorporate a dark spot that is lacking in our common drosophilids (Figure 1). Spotted wing drosophila males and females also have dark bands on their abdomen.

SWD2

Figure 1.   Male spotted wing drosophila. 

Credit: G. Arakelian, Los Angeles County Apricultural Commissioner/Weights & Measures Department

Female spotted wing drosophila possess serrations on their egg laying organ that can cut soft surfaces of sound fruit to lay eggs inside. Common drosophilid flies lack this modification and are limited to laying eggs in soft over-ripe or rotting fruit. Spotted wing drosophila eggs that hatch inside fruit become white maggots that can soften and ruin fruit in the field or can accompany harvested fruit undiscovered until the fruit are in consumers’ hands. Currently, there are no restrictions on fruit from infested farms.

Drosophilids are often called the pomace, vinegar, or fruit flies, but "fruit flies" in this case is confusing since that common name applies to larger flies, the Tephritidae, often prolematic and reported in the news media. Tephritids include banded winged flies such as Mediterranean fruit fly, blueberry maggot fly, Caribbean fruit fly, Oriental fruit fly, Mexican fruit fly, and others. Drosophilid flies are not closely related to tephritid flies and management of the two groups can be different. For instance, rare outbreaks of Mediterranean fruit flies in Florida are managed in part with mass releases of sterilized male Mediterranean fruit flies. This technique has not been developed for drosophilids and is impractical to consider in most cases.

Monitoring and Management

Drosophilids are often called the pomace, vinegar, or fruit flies, but "fruit flies" in this case is confusing since that common name applies to larger flies, the Tephritidae, often prolematic and reported in the news media. Tephritids include banded winged flies such as Mediterranean fruit fly, blueberry maggot fly, Caribbean fruit fly, Oriental fruit fly, Mexican fruit fly, and others. Drosophilid flies are not closely related to tephritid flies and management of the two groups can be different. For instance, rare outbreaks of Mediterranean fruit flies in Florida are managed in part with mass releases of sterilized male Mediterranean fruit flies. This technique has not been developed for drosophilids and is impractical to consider in most cases.

Spotted wing drosophila can survive in Florida's climate and, given the swift colonization of California and spread through Florida, berry growers should be prepared to encounter this fly. The degree of interference to production is clearly unknown, however, management plans are surfacing. Below are tactics that can be applied as conditions warrant. Presently, there are no action thresholds established. Presence of spotted wing drosophila on a farm can be ascertained by sweep-netting and by observing adult flies attracted to strategically-placed clear plastic cups baited with apple cider vinegar (Figure 2). These cups/traps can be hung in strawberry field margins about chest height, protected from the direct rays of the sun, the disturbance by tractor operations, and the disturbance by overhead sprinkler operations. Similarly, in blueberries and cane berries plastic cups can be hung on the south side of the plants away from the morning sun and ~ 1 foot (30 cm) below the top of the bush.

SWD

Figure 2.   Plastic cup baited with apple cider vinegar for monitoring Drosophila suzukii. For best results traps should be placed in shaded areas.
Credit: O.E. Liburd, Department of Entomology and Nematology, University of Florida, Gainesville, FL.. 

Management practices immediately available in Florida for spotted wing drosophila are those used to manage our common drosophilids. The most important progress in managing the new pest will be achieved by implementing cultural practices that deny spotted wing drosophila its breeding sites and kill immature stages inside cull fruit. This can be accomplished in the field by removing marketable berries quickly, before they are infested, and by properly disposing of unmarketable fruit and the immature insects they harbor. Any fruit not to be sold should be collected and buried or sent to municipal disposal sites. It is important to bury fruit at least 1 foot (30 cm) deep, in the case of Florida's sandy soils, to ensure that the insects do not emerge from the soil. If buried too shallow, the fly larvae will crawl to the soil surface, develop to adults, and damage fruit.

Additionally, applications of appropriate insecticides should be made as spotted wing drosophila appears. Insecticides that are useful in controlling adults and approved for various berry crops are listed in Table 1. There are no insecticides available for egg or larva control inside fruit. It is unknown how long pesticide residues could be effective to kill spotted wing drosophila flies under our various cultural conditions, so recurring applications of pesticides at close intervals may be required under heavy pressure, for populations of mixed life stages, or when flies regularly move from outside sources into fruiting fields. When these conditions are absent, applications could be held to one lifecycle or longer, probably 10 days to 2 weeks or longer during much of Florida's fruit production period.

Production by vigilant and responsive berry growers in Florida probably will not be reduced by this new pest, as long as the present management tools remain effective and available and growers cooperate to manage spotted wing drosophila throughout the area. New management tactics must be developed, though, to assure long-term control and to reduce the negative impacts associated with the use of insecticides.

Table 1. 

Insecticides available in Florida that may be useful as sprays for management of Drosophila spp. flies on berry crops.

Active Ingredient
Trade Name
REI1
PHI2
Mode of Action Code3
Blueberry
Blackberry
Strawberry
Raspberry
Bifenthrin
Brigade
12 hours
0 days
3A
X
X
X
X
Fenpropathrin
Danitol
24 hours
24 hours
3A
X
X
X
X
Malathion
Malathion
12 hours
1-3 days
1B
X
X
X
X
Naled
Dibrom
48 hours
1 day
1B
 
 
X
 
Spinetoram
Radiant
4 hours
1 day
5
 
 
X
 
Delegate
4 hours
3 days
5
X
X
 
X
Spinosad
SpinTor
hours
1-3 days
5
X
X
X
X
Entrust
4 hours
1-3 days
5
X
X
X
X
Zeta-Cypermethrin
Mustang Max
12 hours
1 day
3A
X
X
 
X
1Re-entry interval that must elapse between application of the indicated insecticide and entry of any persons into the treated area.
2Pre-harvest interval that must elapse between the application of indicated insecticide and harvest of the crop. PHI varies depending on the berry crop where the product is used. ALWAYS follow label instructions.
3For management of spotted wing drosophila (SWD) resistance to insecticides, growers should use products from one mode of action group during the period of one SWD lifecycle then rotate to another mode of action for a similar period.

New research of Small Fruit and Vegetable IPM laboratory

New article was written by Dr. Liburd and Graduate student Lindsy Iglesias.

Spotted Wing Drosophila: Pest Management Recommendations for Florida Blueberries

An article published by Southern SARE( Sustainable Agricultural Research &Education) highlighting research done by current MS student, Lindsy Iglesias, and Dr. Liburd:

University of Florida exploring IPM Techniques to Control the Spotted Wing Drosophila

Dr. Liburd was invited to discuss blueberry pest management including the management of Spotted wing Drosophila with Dr. Ron Cave.

 

Lindsy Iglesias took 1st place at the annual American Entomological Society meeting for her presentation on "Monitoring, trapping, and behavioral studies of the spotted wing drosophila, Drosophila suzukii (Matsumura), a new pest threatening Florida blueberries" in the MS student competition.

Lindsy Iglesias took 1st place at the annual Florida Entomological Society meeting for her presentation on" Drosophila suzukii Matsumura, a potentially devastating pest in Florida blueberries: Survey and trapping studies" in the MS student competition.

 

     

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