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Spotted Wing Drosophila

Background

Spotted winged drosophila ( Drosophila suzukii) is one of the most recent additions to the list of the invasive species. It does not discriminate against any fruits, vegetables, and/or ornamentals that have soft skin, presenting an easy target for gravid females to deposit their eggs. Among its favorites are peaches, nectarines, plums, cherries, strawberries, grapes, blueberries, raspberries, blackberries, cranberries, currents, gooseberries, tomatoes, saskatoons, mulberries and elderberries.

It is native to Southeast Asia and is a common pest in Japan, China, Russia, Korea, India, Myanmar and Thailand. In the U.S., it was first discovered in Hawaii in early 1980 and has been established there since 1986. California reported its first SWD encounter in 2008. Since then, SWD has been rapidly expanding its distribution range. It can be found up and down the east coast from Florida to Maine. It was first identified in West Virginia in 2011.

Description

The adult flies are only 2 to 3 mm long, have a yellow-brown body color and very big, red eyes. The males have a dark spot at the edge of each forewing and two dark bands on the forelegs. Females do not have these markings; they have very distinctive, serrated specialized organ for depositing eggs, which is capable of slitting through the undamaged fruit skin.

Damage

Damaged fruit becomes soft, appears bruised, collapses on itself and often there is ooze associated with the punctures that facilitate fungal development. Fruit with maggots become unusable, unsellable and the crop is ruined.

Spotted Wing Drosophila – Control Measures

Monitoring for SWD is highly encouraged. Regular checking for the SWD presence in the garden and in the orchard is part of pest management. The apple cider vinegar method is used to monitor for adult fly presence. There is a simple way to construct the traps. All that is needed is a clear plastic container or a sturdy cup 16 to 32 ounces with a removable lid. Drill several small holes (3/16 of an inch) near the rim of the container, leaving 1 to 2 inch area undrilled to facilitate changing bait. Use a wire to construct a handle so that the container can easily be placed on a branch or cane. Pour about an inch of apple cider vinegar into the container as bait. During the season, check traps once or twice every week.

Detecting larval presence in fruit can be done by using the salt extraction method because larvae are very sensitive to salt exposure. Fruit suspected of having maggots inside should be placed in the water-salt solution (1 tablespoon of salt into 1 cup of warm water) in a shallow white container. Larvae will exit the fruit as they try to escape the salt. Very small white larvae will be at the top of the solution before they die and sink to the bottom.

Getting rid of SWD is an unattainable goal. Once detected in the area, every effort to manage it should be put forth.

Sanitation is very important. All ripe and overripe fruit needs to be picked and removed. Research in Oregon suggests that collected fruit can be disposed by being placed in plastic bags and left outside and exposed to the sun for about a week. The high temperature induced by the sun will “cook” the larvae. The other effective method is solarization, which is very similar to the bagging method. The difference is finding an area with full exposure to the sun, placing the fruit directly on the ground and covering it with 2 mm plastic that is pulled tightly over the pile without leaving any air pockets to ensure a good seal. Plastic sheet edges need to be covered by the soil so the plastic does not get picked up and removed by the wind. High temperatures under the plastic will kill all the larvae.

When it comes to gardens and landscapes, there is a potential for biological control. The idea is to have a companion planting that would provide habitat for beneficial insects, like lacewings, and parasitic wasps that would aid in control of SWD.

For the organic production systems, chemical control is rather limited and includes Entrust 80 WP (spinosad) and Pyganic 1.4EC (pyrethrum). There are more options for commercial producers. A complete list can be found through Michigan State University: http://www.ipm.msu.edu/invasive_species/spotted_wing_drosophila.

Spotted Wing Drosophila – Life Cycle

The life span of the adult SWD is approximately two weeks. During that time, a single female can deposit more than 100 eggs in a day or several hundred eggs during her lifetime. There are two to three eggs in each fruit.

Each egg has two “breathing tubes” that stick out of the fruit and look like two, fine hairs. Eggs hatch rapidly and after feeding within the fruit for five to seven days, the larvae are ready to pupate. The pupa is brown and about 3 mm long, resembling a grain of rice. It has two horn-like breathing tubes sticking out of the fruit until the adult flies emerge four to five days after pupation.

The activity and survival of the SWD is highly dependent on weather conditions, mainly temperature. Temperatures above 85 degrees are known to cause males to become sterile. Cold temperatures are a limiting factor as well, though SWD populations are found in cold regions of Japan. Optimal development occurs at temperatures between 65 and 70 degrees, resulting in only 12 days for each generation.


Authors: Mira Danilovich, WVU Extension Service Consumer Horticulture Specialist and
Daniel Frank, WVU Extension Service Entomology Specialist
Last Reviewed: May 23, 2017