Tag: Drosophila suzukii.

Week 8: Spotted Wing Drosophila

Spotted wing drosophila, Drosophila suzukii, is an invasive species that is now found in all 10 Canadian provinces. It was first confirmed to be present in British Columbia in 2009, Alberta in 2010, Manitoba in 2013, and Saskatchewan in 2019. It is still not as widespread in the prairie provinces as in other parts of Canada but is, unfortunately, becoming more common in the prairie region.

Spotted wing drosophila is a significant economic pest of fruits and berries. Unlike other fruit flies that are attracted to ripe or spoiling fruits and vegetables, spotted wing drosophila is capable of laying eggs in fresh, healthy fruits. It is a generalist and is known to feed on fruits in at least 19 plant families.

Adult spotted wing drosophila flies on a raspberry. Photographed by Hannah Burrack, North Carolina State University, Bugwood.org.

Adult spotted wing drosophila are small flies with light brown or dark yellow bodies. There are darker coloured bands on the abdomen and the eyes are dark red. Male flies have grey spots on their wingtips; the wings of female flies do not have spots.

Spotted wing drosophila larva inside a raspberry. Photographed by Hannah Burrack, North Carolina State University, Bugwood.org.

After mating, female flies use their saw-like ovipositor to slice into fresh fruit and then deposit 1-3 eggs into the fruit. Larve develop feeding inside the fruit, causing the fruit to spoil from the inside. It is often difficult to distinguish infested fruit from healthy fruit until after the fruit has been picked and cut open.

Spotted wing drosophila larva inside a blueberry. Photographed by Frank A.  Hale, University of Tennessee, Bugwood.org.

Managing spotted wing drosophila is challenging. Optimal methods for management of spotted wing drosophila in Canada, including biological control, are still being developed and tested. When picking fruit like raspberries and cherries on the prairies where spotted wing drosophila might be present, it is important to quickly clean and store the fruit in the fridge. Cold temperatures help to prevent eggs from hatching and will slow down larval development and feeding activity, helping to preserve infested fruit.

More spotted wing drosophila information (and pictures) is available from the CFIA, Manitoba Agriculture, Government of British Columbia, and the University of Minnesota Extension.

Spotted Wing Drosophila

With the 2022 growing season well underway, we decided to feature an insect that is becoming a growing problem on the Canadian Prairies: Spotted Wing Drosophila (SWD), Drosophila suzukii.

This invasive insect is thought to have originated in southeast Asia. The first record of SWD is from Japan in 1916. SWD is now established in small and stone fruit production areas throughout North America. SWD has been reported in British Columbia since 2009, and was first reported in Alberta in 2010. Occurrence in Alberta, and low levels in southern Manitoba in 2019 suggested that SK infestations were likely imminent. Monitoring for this pest conducted by the Saskatchewan Ministry of Agriculture began in 2019. Populations were detected throughout the province that year, spurring continued monitoring. Data from 2021 and 2022 indicate continued widespread distribution throughout the province. Early season detection of significant numbers suggests overwintering populations on the prairies.

SWD is an economic pest of many soft fruits, including raspberries, strawberries, cherries, blueberries and plums. Saskatoon berry has been documented as a host. Haskap is also considered to be susceptible but may escape major damage, as SWD populations typically do not increase until after harvest. However, Ontario haskap growers have seen economic losses when a mild winter is coupled with factors that lead to delayed ripening. SWD adults are 3-4 mm, yellow-brown with red eyes. Males have a conspicuous spot on the leading edge of each wing (Figure 1).

Figure 1. Spotted Wing Drosophila, male. Photo Credit: Encyclopedia of Life; Martin Cooper; University of Nebraska-Lincoln Dept. of Entomology

Females lack the spots but have a characteristic large, serrated ovipositor (Figure 2).

Figure 2. Spotted Wing Drosophila, female. Photo Credit: Encyclopedia of Life; Martin Cooper, University of Nebraska-Lincoln Dept. of Entomology

SWD overwinter as adults. These become active in the spring, mate and seek egg-laying sites. Female SWD lay as many as 16 eggs per day for up to two months. An average of 384 eggs are produced by each female. With their serrated ovipositor, female SWD deposit eggs under the skin of healthy, ripening fruit. Oviposition sites look like pin-holes in the skin (Figure 3). These can also serve as avenues of entry to pathogens like brown rot and botrytis.

Figure 3: SWD-damaged cherry showing oviposition scars. Photo Credit: Martin Hauser, California Department of Food and Agriculture

Several larvae can occur per fruit (Figure 4). Larval feeding causes fruit to become prematurely soft and unmarketable. Larvae mature in 3-13 days and pupate most commonly in the fruit. The pupal stage lasts another 3-15 days. Multiple generations per year are common.

Figure 4. SWD larva inside raspberry. Photo: Bugwood.org, Hannah Burrack

Although SWD adults can be moved around by winds, movement of contaminated plant material is the major route for initial dispersal. Current management includes culling and destruction of soft fruit and the application of insecticides to limit populations. There are several products registered to control SWD. These can be found here: http://pr-rp.hc-sc.gc.ca/ls-re/index-eng.php. Use the search term ‘spotted wing drosophila’. Product updates occur periodically so check this site regularly.