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Beginner

Scientific Name: Drosophila suzukii

Identification

• SWD attacks thin-skinned fruit such as raspberry, blackberry, blueberry, strawberry, cherry, plum, peach, nectarine, and sometimes grape.
• Adults are small (2-3 mm), red-eyed fly with a pale yellow or brown abdomen marked by dark brown unbroken bands or stripes.
• Males have a distinct black spot towards the tip of each wing (spots not visible in newly emerged males).
• Females lack spots on the wings, but have a saw-like ovipositor which is used to cut into fruit for egg-laying.
• Larvae are tiny (up to 6 mm), white, cylindrical and generally featureless maggots that can be found feeding in fruit.
• Pupae are 3 mm in length, brown, and have two stalks with small finger-like projections on one end.
• Infested fruit over ripens, becoming soft and walls collapse.
• Watch for juice in the cup of the fruit and staining on the receptacle as the fruit is harvested. 

Often Confused With 
Common vinegar fly adult
Common vinegar fly larvae
Sap beetle larvae and raspberry fruitworm larvae

Period of Activity
In Ontario, first flies are trapped in mid-June in early locations. By mid-late July, adults are active in most fruit producing regions. Numbers increase exponentially throughout August and September. The preferred temperature for SWD is between 20 and 25°C, and their activity is reduced when temperatures exceed 30°C or fall below 10°C. There are 3-9 generations of SWD each season and all stages are present throughout the summer and fall.   

When populations are high, SWD adults can be observed resting on fruit and foliage in early morning. Adults are most active in early morning and in the evening and less active in hottest, driest parts of the day.
Raspberry and blackberry fruit are susceptible to SWD when fruit begins to turn colour, although it is most susceptible as it ripens and matures.  

Scouting Notes 
Use baited traps to detect SWD adults early in the season. Traps can be used as an early warning of fly activity, but by the time the first flies are caught in traps, infestation of fruit may have already begun.

Use commercially available traps or construct traps out of plastic containers with lids. Perforate the containers with small holes (aprox 3 mm ) to allow entry of SWD flies and prevent trapping of larger species. Bait traps with a commercially available bait or with apple cider vinegar and a drop of unscented soap. The soap will break the surface tension of the apple cider vinegar, which acts as both a bait and a drowning solution. Check traps regularly and replace bait weekly or per manufacturer’s instructions.  

Place traps in spring, when temperature is consistently over 10°C, and/or when fruit starts to form, at least one month prior to fruit ripening. Once fruit begins to ripen, flies are less likely to be attracted to traps. Place traps in sheltered areas near field edges or in hedgerows, particularly if wild hosts are present. Do not place traps in full sun.

The number of  SWD flies  in traps increases dramatically as summer progresses. Collecting, sorting and identifying SWD in the drowning solution is tedious and time consuming. 

Monitoring fruit for larvae is a more efficient way to monitor for SWD as the season progresses.  Collect ripe, marketable fruit from the edge of the field near woods and bush, and from the lower sheltered parts of the plant canopy to increase the chances of finding SWD. 

Use the salt water test to check for larvae in fruit. Dissolve 1 part salt in 16 parts water. Place a sample of fruit (approx. 100 ripe, healthy-looking fruit) in a shallow dish or tray. Pour salt water over the fruit until fruit is completely covered. Mash fruit lightly with a potato masher. In 10- 15 minutes, larvae will float to the surface of the solution. Look for small, white larvae, tapered at both ends, and 1-4 mm in length. Tally the number of larvae and divide by the number of fruit in the sample to get an average number of larvae per fruit.

Other methods have been used to assess SWD larvae in fruit. These methods are less accurate than the salt water test but can be used to detect SWD and track population trends from week to week.

• Pick 25-50 marketable fruit from the field and place the fruit in a small zip-lock bag. Seal the bag tightly and lay it flat in a warm spot such as the car. SWD larvae will crawl out of the fruit

Threshold
No thresholds established. 

 

Advanced

Scientific Name: Drosophila suzukii

Identification

• SWD attacks thin-skinned fruit such as raspberry, blackberry, blueberry, strawberry, cherry, plum, peach, nectarine, and sometimes grape.
• The adult SWD is a small (2-3 mm), red-eyed vinegar fly with a pale yellow or brown abdomen marked by dark brown unbroken bands or stripes.
• Males have a distinct black spot towards the tip of each wing (spots not visible in newly emerged males).
• Females lack spots on the wings, but have a saw-like ovipositor which is used to cut into fruit for egg-laying.
• Eggs small, white and oblong-shaped, inserted into the fruit with two thread-like breathing tubes extending from the tip of the egg to just above the fruit surface.  
• Larvae are tiny (up to 6 mm), white, cylindrical, tapering to pointed ends and generally featureless maggots that can be found feeding in fruit.
• Pupae are 3 mm in length, brown, and have two stalks with small finger-like projections on one end.
• Infested fruit becomes soft and walls collapse.
• Infested fruit is indicated by juice in the cup of the fruit and staining on the receptacle as the fruit is harvested. 

Often Confused With 

Common vinegar fly adult
Common vinegar flies, (also called fruit flies, or drosophila flies) are similar in size and shape to spotted wing drosphila.  Bands of colour on the body of the common vinegar fly may be broken, while bands on SWD are continuous from side to side. Unlike SWD, common vinegar fly males do not have spots on wings and females do not have a large serrated ovipositor.

Common vinegar fly larvae
It is difficult to distinguish these larvae from SWD. Both appear as small white featureless larvae in fruit. They must be reared to adult to distinguish which species of vinegar fly is present.  However, vinegar fly larvae are found only in injured or overripe fruit, while SWD larvae can be found in fruit that appears to undamaged and mature but not overripe.

Sap beetle larvae and raspberry fruitworm larvae
Beetle larvae are occasionally found in raspberry fruit. All beetle larvae have a distinct brown head capsule and 3 pairs of legs. SWD larvae, as well as vinegar fly larvae, are legless, with black mouth hooks but without a distinct head capsule.

Period of Activity
In Ontario, SWD activity is typically detected in spring, when first flies are trapped in mid-June in early locations. By mid-late July, adults are active in most fruit producing regions. Numbers increase exponentially throughout August and September. The preferred temperature for SWD is between 20 and 25°C, and their activity is reduced when temperatures exceed 30°C or fall below 10°C. There are 3-9 generations of SWD each season and all stages are present throughout the summer and fall.   
When populations are high, SWD adults can be observed resting on fruit and foliage in early morning. Adults are most active in early morning and evening and less active in hottest, driest parts of the day.
Raspberry and blackberry fruits are susceptible to SWD as they begin to turn colour but most damage occurs when fruits are ripening or mature.

Biology
SWD have a life cycle containing an egg stage, 3 larval instars, a pupal and an adult stage. Eggs, larvae, and pupae are present inside the fruit. Full development from egg to adult can take between 8 and 25 days depending on temperature.

SWD overwinters as a specialized (darker) adult morph that has greater cold tolerance than the summer form. They overwinter in sheltered locations and beneath debris in woods and hedgerows.  Overwintered flies emerge in spring and feed on nectar from early flowering weeds and crops. Overwintering adults may live for more than 200 days, but the longevity of the summer form is considerably less.

SWD female flies lay eggs in the ripening fruits of a wide range of host plants, including many wild, uncultivated species. Each female may produce 100–400 eggs, laying approximately 20 per day (depending on host availability and environmental conditions).

Larvae hatch and feed in the fruit, liquefying the fruit tissue and rendering it unmarketable. Disease pathogens can also enter through the egg-laying holes, causing further deterioration of the fruit. 
Mature larvae pupate in the fruit or drop to the ground where they pupate in debris near the soil surface. 

Wild hosts play an important role in the biology of SWD.  Plants that can support build-up of SWD populations include honeysuckle, brambles, mulberry, pin cherry, elderberry, dogwood, pokeweed, buckthorn, yew and purple flowering raspberry. There can be multiple overlapping generations each year.

SWD move back to woods and wild, vegetated, sheltered areas in the autumn as fruit crops are harvested.

Scouting Notes 
Use baited traps to detect SWD adults early in the season. Trapping is most useful when done in conjunction with a regional monitoring program. Traps can be used as an early warning of fly activity, but by the time the first flies are caught in traps, infestation of fruit may have already begun.

Use commercially available traps or construct traps out of plastic containers with lids. Perforate the containers with small holes (aprox 3 mm ) to allow entry of SWD flies and prevent trapping of larger species. Bait traps with a commercially available bait or with apple cider vinegar and a drop of unscented soap. The soap will break the surface tension of the apple cider vinegar, which acts as both a bait and a drowning solution. Check traps regularly and replace bait weekly or per manufacturer’s instructions.  

Place traps in spring, when temperature is consistently over 10°C, and/or when fruit starts to form, at least one month prior to fruit ripening. Once fruit begins to ripen, flies are less likely to be attracted to traps. Place traps in sheltered areas near field edges or in hedgerows, particularly if wild hosts are present.

The number of SWD flies in traps increases dramatically as summer progresses. Collecting, sorting and identifying SWD in the drowning solution is tedious and time consuming.

Monitoring fruit for larvae is a more efficient way to monitor for SWD as the season progresses.  Collect ripe, marketable fruit to assess SWD. Collect fruit from the edge of the field near woods and bush, and from the lower sheltered parts of the plant canopy to increase the chances of finding SWD. 

Use the salt water test to check for larvae in fruit. Dissolve 1 part salt in 16 parts water. Place a sample of fruit (approx. 100 ripe, healthy-looking fruit) in a shallow dish or tray. Pour salt water over the fruit until fruit is completely covered. Mash fruit lightly with a potato masher. In 10- 15 minutes, larvae will float to the surface of the solution. Look for small, white larvae, tapered at both ends, and 1-4 mm in length. Tally the number of larvae and divide by the number of fruit in the sample to get an average number of larvae per fruit.

Other methods have been used to assess SWD larvae in fruit. These methods are less accurate than the salt water test but can be used to detect SWD and track population trends form week to week.

• Pick 25-50 marketable fruit from the field and place the fruit in a small zip-lock bag. Seal the bag tightly and lay it flat in a warm spot such as the car. SWD larvae will crawl out of the fruit.
• Or place 25-50 fruit in a single layer in a small dish in the freezer.  As the temperature drops, larvae will exit the fruit. 

Threshold
No thresholds established. 

Management Notes
SWD management requires multiple approaches, including crop management, harvest management and the use of insecticides. Ripening fruit is susceptible if SWD flies are present in the area.  

• Prune and trellis raspberry plants to facilitate harvest and good spray coverage.
• Control weeds in the row to encourage air movement through the canopy and to reduce sheltered, humid areas which favour SWD.
• Harvest fruit early, thoroughly and often. All mature fruit should be harvested every day or every other day.
• Store unmarketable fruit in sealed containers where it can ferment for 3 days before disposal. 
• Apply insecticides weekly when flies are present and fruit is ripening, especially during periods of high SWD pressure.
• For fall-bearing raspberries, strip ripening fruit off the lower parts of the plant until there is enough fruit to harvest every 2 days. Begin a regular insecticide program as primocane fruits begin to ripen. Do not let SWD build up on the small crop that develops early at the base of the plant.
• Consider exclusion netting as an option in smaller blocks of high value fruit.
• See OMAFRA Publication 360: Fruit Crop Protection Guide (Chapter 3: Berry Crops) for a list of registered insecticides and watch OMAFRA information sources for temporary emergency use registrations.
• See ontario.ca/spottedwing for updated information on wild hosts, monitoring, management and annual trends.