By: Jackie Carroll
If you have a problem with withering and browning fruit, the culprit may be the spotted winged drosophila. Find the information you need on spotted winged drosophila control in this article.
What is Spotted Winged Drosophila?
Native to Japan, spotted winged drosophila was first discovered on the U.S. mainland in 2008 when it infested berry crops in California. From there it quickly spread across the country. It is now a serious problem in areas as far away as Florida and New England. The more you know about these destructive pests, the better you will be able to deal with them.
Known scientifically as Drosophila suzukii, the spotted winged drosophila is a tiny fruit fly that ruins orchard crops. It has distinctive red eyes, and the males have black spots on the wings, but since they are only one-eighth to one-sixteenth of an inch long, you may not get a good look at them.
Break open damaged fruit to look for the maggots. They are white, cylindrical and a little more than one-eighth of an inch long when fully mature. You may find several inside a single fruit because the same fruit is often stung more than once.
Spotted Winged Drosophila Life Cycle and Control
The female flies puncture or “sting” fruit, depositing one to three eggs with each puncture. The eggs hatch to become maggots which feed inside the fruit. They complete the entire life cycle from egg to adult in as little as eight days.
You may be able to see the speck where the female fly stung the fruit, but most of the damage comes from the maggots’ feeding activity. The fruit develops sunken spots, and the flesh turns brown. Once the fruit is damaged, other types of fruit flies invade the crop.
Treating fruit for spotted winged drosophila pests is difficult because once you discover that you have a problem, the maggots are already inside the fruit. At this point, sprays are ineffective. Preventing spotted winged drosophila from reaching the fruit is the most effective method of control.
Keep the area clean by picking up fallen fruit and sealing it in sturdy plastic bags for disposal. Pick damaged or stung fruit and dispose of it in the same way. This may help reduce damage to late-ripening and unaffected fruit. It also helps protect next year’s crop. Keep the insects away from small trees and berry crops by covering them with fine netting.
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Drosophila suzukii, commonly called the spotted wing drosophila or SWD, is a fruit fly. D. suzukii, originally from southeast Asia, is becoming a major pest species in America and Europe, because it infests fruit early during the ripening stage, in contrast with other Drosophila species that infest only rotting fruit. 
Native to southeast Asia, D. suzukii was first described in 1931 by Matsumura, it was observed in Japan as early as 1916 by T. Kanzawa. 
D. suzukii is a fruit crop pest and is a serious economic threat to soft summer fruit i.e., cherries, blueberries, raspberries, blackberries, peaches, nectarines, apricots, grapes, and others.  Research investigating the specific threat D. suzukii poses to these fruit is ongoing. 
Unlike other vinegar flies that occur in California, spotted-wing drosophila is a significant pest that attacks healthy fruit prior to harvest. As fruit integrity is compromised by oviposition and larval feeding, common vinegar flies (i.e., Drosophila melanogaster) may also oviposit in the damaged fruit. Damage can also provide entry for infection by secondary fungal and bacterial pathogens, but this is not always the case. Often damage is not seen until the fruit is at the market fruit is soft and has a reduced shelf-life.
Oviposition creates a small depression ("sting") on the fruit surface. Many larvae are possible within a single fruit because females can lay more than one egg in each fruit and multiple females will oviposit on the same fruit. Maggots develop and feed inside the fruit, causing the flesh to turn brown and soft. When infested fruit are gently squeezed, fluid exudes out of the hole in the fruit surface where the egg was laid.
What is the Difference Between SWD and Regular Fruit Flies?
The difference between the SWD and regular fruit flies, besides the tell-tale black spot on the male fly’s wings, is that while everyday fruit flies generally lay eggs in overripe or damaged fruit, Spotted Wing Drosophila have a more aggressive approach. They lay their eggs in the flesh of underripe fruit, making it hard to beat the bugs to the harvest. The eggs hatch, and those nasty little raspberry worms are soon to follow.
These pests are actually relatively new here, and are becoming a HUGE pain to berry growers across the US. Not only do they effect raspberries, but blackberries, blueberries, cherries and strawberries as well.
How to Manage Pests
Spotted wing drosophila—Drosophila suzukii
Larvae of the spotted wing drosophila (SWD, Drosophilidae) feed in cherries throughout the state and in blueberries and occasionally caneberries and strawberries mostly in coastal areas.
The legless, whitish larvae at maturity, and the cylindrical, brown to yellow pupae, are about 1/8 inch long. Adults are flies about 1/10 inch long with red eyes and a brown thorax. The female's egg laying creates a small puncture in a depression on the fruit surface.
Male D. suzukii can be distinguished from most other Drosophila spp. by the dark spot near the tip of each of their two wings. Other similar-looking Drosophila spp. vinegar flies, or common fruit flies, mostly feed in fermenting, injured, or overripe fruit.
Larvae of true fruit flies (Tephritidae) also feed in the pulp of fruits and certain other crops. Pest tephritid flies in California include apple maggot (Rhagoletis pomonella), olive fruit fly (Bactrocera oleae), and walnut husk fly (Rhagoletis completa). Adult tephritids and mature larvae (pale maggots) are about 1/4 inch long, considerably larger than the spotted wing drosophila and other vinegar flies.
Exotic tephritids such as the Mediterranean, Mexican, and Oriental fruit flies are periodically introduced and have apparently been eradicated. Take any tephritid flies or maggots you find in fruit to the county agricultural commissioner or your local UC ANR Cooperative Extension office for identification unless you are confident the species found is already known to be established in California.
Spotted wing drosophila adult females lay eggs in fruit just as it begins to develop its mature color. One to several larvae feed in each fruit, causing it to soften and become decayed. After maturing, the larvae partially or completely exit the fruit to pupate. There may be up to 10 generations per year.
Spotted wing drosophila attacks healthy ripening fruit and damaged or split fruit. The female's ovipositor creates a small puncture in a depression on the fruit surface. Maggots feeding inside the fruit cause the flesh to turn brown and soft. Fruit may decay from secondary fungal and bacterial pathogens and drop.
Traps help detect the presence of spotted wing drosophila. If trapping identifies that SWD is present, or you had this problem last year, insecticide can be applied.
Removing and destroying infested fruit and fruit on the ground may help to reduce infestation of later-maturing varieties. Fine netting ≤0.98 mm mesh (e.g., made for no-seeums) placed over hosts before fruit begins to color or ripen may help to reduce infestation if it is well secured to exclude the flies.
Spotted wing drosophila can be controlled by applications of spinosad, if the sprays are well timed. Monitor fruit and make the first application when fruit begin to change to their mature color. Because some varieties ripen early, others late, and more than one variety may be grown together, the total number of applications depends on what varieties are grown and temperature.
In cherries, make the first application as fruit turns from yellowish to pink (about 2 to 3 weeks before harvest). Spray each variety at least a second time 7 to 10 days later, the shorter interval if temperatures have been warm and longer when it's been cool.
In blueberries, apply an insecticide when the first berries begin to turn from green to pink. Make a second application prior to harvest. Treatments may be warranted at 7- to 14-day intervals until harvest is over.
Adult male spotted wing drosophila
Egg-laying puncture in a depression
Larva exiting a damaged cherry
Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California
What Is Spotted Winged Drosophila - Preventing Spotted Winged Drosophila In Gardens - garden
Spotted Wing Drosophila (SWD) is not a new pest – they were first seen in the continental U.S. in 2008 and have since spread from the west coast to the east coast. SWD is drawn to fruits and berries where they will then infest the produce. These flies tend to prefer softer-skinned fruits like raspberries or peaches. Noticeable damage occurs when the fruit’s skin has been split or damaged in some way. SWD love digging into fruit that is ripe or overripe.
There is hope for preventing SWD infestations though, thanks to insect netting and an experimental co-owner of a berry farm in New York, Dale Ila Riggs. In the fall of 2011, Riggs began to notice the arrival of these pests and her farm, The Berry Patch, was infested within a year. However, she was determined not to be beaten by this pesky insect, so she began years of extensive trials to determine how best to protect her crop.
From 2013 to 2017, Riggs tried everything from spraying with pesticides to using three different types of insect netting. After years of experimenting and analyzing the results of different crop treatment methods, she has determined that 80-gram insect netting is the most efficient way to keep her berries from being ravished by the SWD population. Riggs was able to achieve a 0% infestation rate with the use of her netting by 2016 as opposed to the 60% infestation rate with a sprayed, treated control in 2014.
The Berry Patch co-owner was so impressed with the results she found that she decided to invest in netting for her entire crop. “[The netting] does more than protect from SWD,” Riggs explained. “You have to look at it as an investment.”
Acadian Industrial Textiles offers insect netting for the exclusion of pests, such as SWD. Use our insect netting at the first sighting of adult flies to prevent further damage or infestation. Knowing when to cover your crop is key. If you cover the produce too early, you can prevent pollinating insects from getting to your flowering plants. If you cover the produce too late, you will trap the adults under the netting, possibly making the infestation worse. This means you’ll need to monitor your produce carefully to get the timing right.
Knowing when to cover your produce can be tricky, but with proper monitoring, management, and use of the right insect netting, you can beat Spotted Wing Drosophila and keep your produce fresh and healthy.
For more in-depth information on Spotted Wing Drosophila, read the full article from Oregon State University.
For more about Dale Ila Riggs’ experimental trials with Spotted Wind Drosophila treatments, read the full article from Growing Produce.
The section below contains highly relevant resources for this species, organized by source. Or, to display all related content view all resources for Spotted Wing Drosophila.
Washington State Recreation and Conservation Office. Washington Invasive Species Council.
North Central Integrated Pest Management Center.
Florida Department of Agriculture and Consumer Services. Division of Plant Industry.
Utah State University Extension Utah Plant Pest Diagnostic Laboratory.
Michigan State University. Integrated Pest Management Program.
The Spotted Wing Drosophila (SWD) is a vinegar fly of East Asian origin that can cause damage to many fruit crops. This small insect has been in Hawaii since the 1980s, was detected in California in 2008, spread through the West Coast in 2009, and was detected in Florida, Utah, the Carolinas, Wisconsin and Michigan for the first time in 2010. This website will be the central location for dissemination of information about this insect. Check back for updates. This team is also helping to coordinate research projects to understand how best to protect fruit from infestation by this new pest.