Identification: Spotted Wing Drosophila in Ontario
Table of Contents
The SWD adults and larvae are very similar in appearance to the common vinegar fly normally associated with over-ripe, decaying or damaged fruit. They are not closely related to the much larger fruit fly maggots found in fruit, such as the apple maggot, the blueberry larvae, and the cherry fruit fly.
Adult SWD are small (2-3 mm), with red eyes and short stubby antennae. The abdomen is a pale yellow or brown and marked by dark brown complete unbroken bands or horizontal stripes.
- Males have a distinct black spot towards the tip of each wing and short, stubby antennae. The front feet have dark combs on the first and second segment, with 3 to 6 "teeth" each (Figure 1).
- Females are slightly larger than males and lack spots on wings. Females have, a saw-like ovipositor, with a serrated edge that is darker than the rest of the ovipositor (Figure 2 & 3).
Figure 1: Adult male SWD are small (2-3 mm) light yellow or brown flies. Wings have a single spot close to the tip, and centered around the first wing vein. The antennae are short and stubby. The front feet have dark combs on the first and second segments.
Figure 2: Wings of females lack spots. As with males, the dark bands at the edge of each abdominal segment are unbroken when viewed from above. Note the egg is still attached. Photo credit: E. Beers, Washington State University.
Figure 3; Females have a well-developed saw-like ovipositor. The serrated edge is much darker than the rest of the ovipositor. Note the egg that is still attached. Photo credit: E. Beers, Washington State University.
SWD eggs are laid under the skin of ripening fruit. They are translucent white, elongate, and about 0.6 mm long X 0.18 mm wide. Each egg has a pair of thread-like "breathing tubes" that protrude from the oviposition puncture and are visible on the fruit surface (Figure 4).
Figure 4: The egg's thread-like breathing tubes protrude from the oviposition puncture and are often visible on the fruit surface. Photo Credit: Dr. Ward Strong, FLNRO, Kalamalka Forestry Centre, Vernon
Larvae are found inside the fruit. SWD larvae pass through three instars, each instar becoming progressively larger. Third instar larvae are up to 4mm in length, white, cylindrical, and tapered at both ends. There is no head capsule. With magnification, dark mouth hooks at the front end and a pair of tan caudal spiracles at the rear end are visible (Figure 5). A single fruit may be infested with multiple larvae. After maturing, the larvae partially or completely exit the fruit to pupate. Larvae must be reared to adults for positive identification.
Figure 5: Larvae are up to 4 mm at maturity, have no distinct head capsule, and are tapered at both ends. Photo credit: D. Muller, OMAFRA
SWD pupae are cylindrical brown, and approx. 3 mm in length (Figure 6). Pupae have, two stalks with small finger-like projections on one end which sometimes protrude from infested fruit (Figure 7).
Figure 6: Pupae: 3 mm long, brown,
Photo credit: T. Wallace, OMAFRA
Figure 7: SWD pupae protrude from
fruit before adults emerge.
Photo credit: R. DeJong, OMAFRA
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