Spotted Wing Drosophila (SWD)
The spotted wing drosophila is a small fly that can cause significant damage in berry and tree fruit crops.
Check out the Ministry of Agriculture's SWD Pest Alert page for more information.
Adult flies are brown, 2-3 mm long with red eyes and clear fly-like wings. Male flies have black spots on the end of each wing. Females have no spots but have a saw-like egg laying device (ovipositor) which enables them to cut into fruit and lay eggs inside.
Spotted wing drosophila overwinters as adult flies. In spring, flies become active, mate and lay eggs in ripening fruit. A generation can take 8-21 days, depending on temperature. Up to 4 generations per year are expected in British Columbia.
Numerous crops can be infested with SWD, including blueberry, raspberry, strawberry, blackberry, cherry, peach, and grape. Alternate non-crop hosts can include blackberry, other berries, and seedling cherry.
Unlike most small flies which infest decaying fruit, SWD females lay their eggs inside ripe fruit before harvest. Larvae hatch and begin to feed within the fruit, causing softening and fruit collapse. Contaminated fruit is unmarketable.
Management / Cultural Control:
- Alternate hosts near crop fields should be controlled or mowed to prevent fruiting.
- Remove or bury cull fruit. Keep equipment and processing areas free of old fruit.
- Good field care: decreases humidity in the field with adequate pruning and weed control.
- Be aware of host plants in adjacent fields and encourage neighbours to manage SWD.
- Overripe fruit is more likely to be infested with SWD. Pick early, clean and often.