Land & Environment

USU Extension Researchers Spot New Pest in Utah

Utah State University Cooperative Extension researchers recently discovered the Spotted Wing Drosophila (SWD) in a raspberry and blackberry field in Davis County. The invasive insect is native to Asia and is different from common Drosophila vinegar flies in that, in addition to laying eggs in ripe, over-ripe and spoiled fruits, the females can also lay eggs in under-ripe fruit still maturing on the plant.
 
According to Diane Alston, Utah State University Cooperative Extension entomologist, SWD attacks a broad range of fruits including tree fruits, berry fruits and vegetable fruits. Any soft-skinned fruit may be susceptible to SWD.
 
“We don’t know yet if SWD will over winter in northern Utah, but we suspect that it could in southern Utah based on its temperature tolerance,” she said. “We also don’t know if it will spread quickly and become common in Utah’s fruit-producing regions or if it will be a minor pest. We suspect that it was introduced to Utah in contaminated produce shipped from another state where it occurs.”
 
Because this pest is widespread in the western and southeastern United States, it is considered non-actionable, meaning no import or export restrictions or quarantines will be implemented, Alston said. SWD can be easily controlled using standard insecticides and by expanding the spray program to pre-and post-ripe fruit stages. However, control is not recommended unless SWD is caught in monitoring traps, fruit injury is detected or high-value crops need protection. Inexpensive vinegar fly traps can be used for effective SWD monitoring. Clear plastic cup traps and liquid baits can be homemade, and commercial traps are available. Information on baits and control can be found at the Cooperative Extension website.
 
“The damaging stages of SWD are larvae, called maggots, and adult flies,” she said. “Larvae feed inside fruit causing abscesses, and secondary fungal and pest infection may occur. The adults cause superficial scarring by sawing into the fruit to lay eggs. They prefer to feed on damaged or fermenting fruit.”
 
Alston said the typical vinegar fly is 0.1 inch long with red eyes, a pale brown body and featherlike antennae. Male SWD flies have one dark spot per wing, but females don’t have spotted wings. The eggs are small, white and are inserted into the fruit. More than 350 eggs may be laid by a single female.
 
If suspect SWD are found, Alston recommends sending the specimen(s) to the Utah Plant Pest Diagnostic Lab (435-797-2435) for identification. Information on SWD and other posts is available online.
 
Writer: Julene Reese, 435-797-0810
Contact: Diane Alston, 435-797-2516

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