Spotted Wing Drosophila

Adults are small tan flies with red eyes. Males have a single dark spot near the tip of each wing, giving the pest its name, while females lack the spots but have a large, serrated ovipositor visible under magnification. Larvae are tiny white maggots found inside soft fruit.

Because the flies resemble common vinegar flies, confirmation often relies on the wing spots in males and the ovipositor in females, together with finding maggots in sound rather than rotten fruit. Egg-laying scars and small breathing tubes protruding from the fruit surface are additional signs.

Females lay eggs in ripening fruit, and larvae feed inside before pupating in or near the fruit. The life cycle is very short in warm weather, so populations can build extremely quickly during the fruiting season and produce many overlapping generations, creating intense pressure at harvest time.

The fly can use many cultivated and wild soft-fruited hosts, and wild hosts around fields serve as reservoirs. Its rapid reproduction and wide host use make sustained, well-timed management necessary through the ripening period.

Egg-laying and larval feeding cause fruit to soften, sink, and collapse, and the wounds admit rots and other vinegar flies, accelerating breakdown. Because attack occurs on sound, ripening fruit near harvest, even low infestation can render fruit unmarketable and cause rejection of consignments.

Preferred hosts are soft and stone fruit, including blueberry, cherry, raspberry, strawberry, and blackberry, with grape also affected. Thin-skinned, soft fruit is generally most vulnerable.

Baited traps using fermenting attractants detect adult activity and help time management, and fruit sampling — floating or inspecting fruit for eggs and maggots — assesses infestation directly. Monitoring should intensify as fruit begins to ripen, when the crop becomes susceptible and pressure typically rises.

Management combines sanitation, harvest practices, exclusion, and monitoring within integrated pest management, because the short life cycle and attack on sound fruit leave little margin for error.

• Harvest frequently and completely, and promptly remove or destroy culls and dropped fruit that breed flies
• Cool fruit quickly after harvest to limit larval development in picked fruit
• Use exclusion netting on high-value plantings where practical
• Manage wild and unmanaged host plants around fields where feasible
• Time any treatment using trapping and fruit sampling, and rotate modes of action to slow resistance