Spotted wing drosophila
Spotted wing drosophila (SWD), is an invasive vinegar fly native to Southeast Asia. This invasive fly is very similar in size and appearance to the common fruit fly. It was first discovered in the continental United States in California in 2008. SWD quickly spread throughout the Pacific Northwest and Canada, and was found in Florida in 2009. At least 45 states have now reported SWD, with Michigan and Wisconsin first reporting the insect in 2010. Breeding populations and fruit infestations in Wisconsin were reported in 2012 and were most severe in fall-bearing raspberries. This can be an economically devastating insect for fruit growers.
Fly emergence this year began in western Wisconsin around June 21.
The female SWD has a serrated ovipositor that allows her to cut into healthy fruit to lay eggs. Larvae feed within healthy fruit tissue causing tissue collapse within a few days; consequently crop loss can be severe. SWD adults are small, 1/16 to 1/8 inch long with red eyes and a light brown thorax and abdomen. SWD eggs are tiny and white, and larvae are cream-colored, wormlike, legless, and up to 1/8 inch long.
SWD prefers thin-skinned, soft-fleshed fruit and is primarily a pest of berry crops, including blackberries, raspberries, strawberries, blueberries, and currants. Grapes and tree fruits are also hosts for SWD, as are non-edible fruiting plants such as snowberry, pokeweed, dogwood, honeysuckle, bittersweet nightshade, as well as buckthorn.
SWD prefers moderate temperatures and can complete a generation in as little as eight to nine days. SWD adults live for about two weeks and females can lay more than 300 eggs during this time. Females lay from one to three eggs per fruit and several females can lay eggs in a single fruit. Eggs hatch in as little as one to three days. Larvae can complete feeding within just a few days and can pupate in the damaged fruit or in the top layers of leaf litter around infested plants. Because of their short generation time, large SWD populations can build up, especially if the insect is left uncontrolled.
The first and most important step in SWD management is to determine whether SWD is present. Use trapping of adult flies for early SWD detection and to monitor trends in adult populations
To control SWD, remove alternative hosts such as wild blackberries, wild raspberries, wild plums, and wild grapes, which can serve as a reservoir for SWD. When growing fruit crops that are preferred hosts for SWD, be sure to harvest fruit promptly, and remove and destroy overripe or infested fruit to help minimize the buildup of SWD.
Exclusion netting with a fine mesh or row covers can be used prior to fruit ripening to keep SWD away from fruit. Use traps to monitor for the presence of SWD adults. As needed, use broad-spectrum insecticides for control. Products containing carbamates, organophos-phates, pyrethroids and spinosyns are available for use in conventional production.
Spinosad and pyrethrum are available for use in organic production. Spray thoroughly in the plant canopy to kill adults before they are able to lay eggs in the fruit. Because you are applying insecticides to an edible crop, be especially aware of any preharvest interval (PHI) restrictions of the product that you select.
A recently developed guide available at https:www.canr.msu.edu/ipm/uploads/files/SWD/SWDOrganicBerryCrops.PDF provides a list of insecticide and non-chemical approaches to protect berry crops against SWD.