A pest that has targeted strawberries and other soft fruits in Manitoba could be headed west.
The spotted wing drosophila, which is thought to have come from southeast Asia, has been spotted in Manitoba in small numbers. SWD’s presence in Alberta and British Columbia suggests Saskatchewan may be the bug’s next home.
SWD is an economic pest of soft fruits including raspberry, strawberry, cherry, blueberry, haskap and plum. Saskatoon berry has also been documented as a host.
Adult SWD have yellow-brown bodies that are three to four millimetres long, and have red eyes. Males have a conspicuous spot on the leading edge of each wing. Females lack the spots but have a large, serrated ovipositor.
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, averaging 384 eggs each. The females deposit the eggs under the skin of healthy, ripening fruit. Oviposition sites look like pinholes in the skin.
These sites can be entry points for pathogens like brown rot and botrytis. Several larvae can occur per fruit. Larval feeding causes fruit to become prematurely soft and unmarketable. Larvae mature in three to 13 days and pupate most commonly in the fruit. The pupal stage lasts another three to 15 days. Multiple generations per year are common.
Although SWD adults can be moved around by winds, movement of contaminated plant material is the major route for dispersal. Current management includes culling and destruction of soft fruit and the application of insecticides to established populations.