Spotted wing drosophila

Spotted wing drosophila (Drosophila suzukii) is a small fruit fly in the family of Drosophilidae.

Adults

• Adults are about 2–3mm long with a wingspan of 6–8mm. Males are typically smaller than females.
• Males have a dark spot on the distal margin of each wing; females do not.
• Females have a dark brown to black ovipositor with sawtooth edges that they use to puncture the skin of fruit for laying eggs.
• Males and females have distinct big red eyes.

Eggs

• Eggs are oval and white, about 0.4–0.6mm long and 0.2mm wide.

Larvae

• Larvae are a typical maggot shape with a white body and black mouthpart.
• Larvae have 3 instar stages and grow up to 6mm long and 1mm wide.

Pupae

• Pupae are spindle-shaped, reddish brown, about 2–3mm long and 1–1.5mm wide.
• Pupae have 2 small finger-like projections on one end that they use for breathing.

Plant stage and plant parts affected

• SWD attacks fruiting plants and harvested fruit including healthy ripening fruit, overripe fruit and damaged fruit.

Plant damage

• Females penetrate the skin of soft-skinned fruit when laying eggs, leaving scars on the surface.
• Most damage is caused by the larvae feeding on the pulp inside the fruit. The infested fruit becomes wrinkled, forms craters and eventually collapses around the feeding site.
• The wounded fruit is susceptible to secondary microbe infection, which leads to rot and decay.

SWD is similar in size and shape to many vinegar fly species. However, most vinegar flies are saprophagous—they feed on only overripe and fallen fruit or other decaying plant matter. SWD feeds on these but also attacks fresh and healthy ripening fruit, often before harvest.

SWD is widely distributed in temperate and subtropical Asia, its presumed native range.

It has spread extensively to continental America and Europe, and has a limited distribution in Africa and the Middle East.

SWD has a broad host range but prefers soft-skinned fruit including:

• cherries
• blueberries
• raspberries
• blackberries
• strawberries
• grapes
• common figs
• stone fruit
• Asian pears.

• Adult females lay their eggs in the fruit. Egg-laying can last for 10–65 days with up to 21 eggs laid per day.
• Within 3 days, the eggs hatch into larvae (maggots). They feed inside the fruit, causing the fruit skin to collapse and the fruit to turn soft and begin to rot.
• After 3 larval stages (5–13 days), the larvae pupate mostly in the fruit but sometimes in the soil.
• Depending on a range of factors, including temperature, it takes 3–15 days for adult flies to emerge.
• The life span of adults can be as short as 8–14 days or as long as 3–9 weeks at optimal conditions.
• SWD spend winter as adults. Their activities are suppressed by cold temperatures, and they become active again in spring.
• The number of generations per year ranges from 3 to 13 depending on climatic conditions.

SWD poses a significant threat to Australian fruit industries. It can damage a wide range of fruit crops at pre-harvest and post-harvest stages.

SWD infestation could reduce crop yield and impact marketability. In the United States, SWD infestation has led to crop losses of 20–50%, plus costs to manage the pest.

If SWD was introduced to Australia, the impact across various industries could be substantial. Industries facing potential threats include:

• berries, valued at about $1.03 billion
• stone fruit, valued at about $338.9 million
• table grapes, valued at about $722.2 million (Source: Hort Innovation—Australian Horticulture Statistics Handbook 2021/22 (PDF, 9MB)).

Also, there would be a significant economic impact on Australia's wine industry, which:

• is world's fifth-largest producer of wine grapes
• produces 1.75 million tonnes of grapes annually
• produces 1.2 billion litres of wine annually (Source: Wine Australia).

SWD are not strong flyers but they can fly short distances when searching for suitable host plants and microclimates.

The rapid global spread of SWD is most likely through human-assisted transport of infested fruit.

• Regularly inspect fruit crops, particularly any soft-skinned fruit that had no previous problems with fruit fly at ripening stage but are now infested with maggots and fruit flies that are 2–3mm long.
• Monitor non-commercial hosts for SWD.

Check these resources to help protect your farm from plant pests and diseases:

• Protecting your farm
• Cherry growers' biosecurity manual (PDF, 4.3MB)
• Orchard biosecurity manual for the summerfruit industry (PDF, 3.1MB)
• Vineyard biosecurity manual (PDF, 2.9MB)
• Farm biosecurity.

SWD is a national priority plant pest. If you think you have found SWD, you must take all reasonable and practical steps under your control to minimise any associated risks. This is your general biosecurity obligation (GBO).

Report suspected SWD:

• online
• by calling Biosecurity Queensland on 13 25 23
• by calling the Exotic Plant Pest Hotline on 1800 084 881.

If you plan to import fresh fruit, check the Australian Government's conditions for importing plants and plant products.