1. Swede Midge Introduction, Damage and Biology
Cornell Cooperative Extension
Swede Midge Introduction, Damage and Biology
Christy Hoepting
Cornell Cooperative Extension
Vegetable Program

2. Swede Midge Serious insect pest of cruciferous plants:
vegetables (i.e. broccoli, cauliflower, Brussels sprouts, cabbage, collards, swede/turnip, Asian vegetables (i.e. bok choy, etc.)
canola
weeds (i.e. shepherd’s purse, wild mustard)
Ornamental crucifers
Common and endemic in Europe:
Known since late 1800s
Major pest in Belgium, Germany, Switzerland, Netherlands, France, Poland and Slovania

3. Swede Midge in North America
2000: first identification in Ontario, Canada (Hallett & Heal)
Symptoms observed at least since 1996, but erroneously attributed to a molybdenum deficiency
Economic losses occur in Canada and in parts of New York State:
up to 85% losses
Especially in organic and small-scale operations

4. Swede Midge: Adult Adult female Adult male
Swede midge is a tiny fly, less than 2 mm in size, which is difficult to distinguish from other midges except by a specialist.

5. Swede midge: eggs Length: 0.3 mm Width: 0.08 mm
Swede midge females lay their eggs deep in the heart of cruciferous plants. They like the youngest actively growing tissue. Eggs are initially transparent becoming creamy yellow as they near maturity, and microscopic and cannot be seen with the naked eye.
Deep in the youngest actively growing vegetative tissue

6. Swede midge: larvae 0.3 to 3-4 mm
Eggs hatch into larvae, which are 3-4 mm in size at maturity. They are clear when they first hatch and become more creamy white or yellow. As they near maturity, they have the capability to curl up and flip or jump off of the plant to the ground. Swede midge larvae feed gregariously (in groups), during feeding, larvae produce a secretion that breaks down plant tissue, creating a moist environment. The secretion is toxic to the plant and results in swollen tissue, abnormal growth and brown scarring that ultimately can result in reduced yield and unmarketable produce.

7. Damage: Blind head, brown scarring at growing point
broccoli

8. Damage: Leaf puckering
Green cabbage

9. Damage: Leaf puckering
broccoli

10. Damage: Leaf puckering
Red cabbage

11. Damage: Leaf puckering
cauliflower

12. Damage: Multiple shoots, growing points
broccoli

13. Damage: Multiple small heads
Red cabbage

14. Damage: Brown corky scarring in head
Brown corky scarring is not limited to the growing points and leaf petioles, but can also cause damage in the heads of cauliflower…
cauliflower

15. Damage: Brown corky scarring in head
broccoli

16. Damage: Brown corky scarring in head
Green cabbage

17. Damage: Secondary soft rot

18. Swede midge larvae in an infested growing tip
Peel back leaves of suspect growing tip and look for larvae. SM larvae break down plant tissue creating a very moist environment – you will see the moisture in an infected tip compared to a healthy one.

19. Damage: Swollen Flower Buds
Another place to look for swede midge larvae is in swollen floret in broccoli for example. Peel them open and you might find swede midge larvae!

20. Damage: Swollen Florets
Another place to find swede midge larvae are in swollen florets in broccoli for example. Peel them open and you might find SM larvae.
broccoli

21. Swede midge damage in canola
Canola is another host for swede midge. Affect on yield depend on the stage of canola when it becomes infested.

22. Swede midge damage on weeds
Field pennycress
Example of weed infested with swede midge, see the swollen leaf petioles.

23. Swede Midge Damage Severity
Increases…
as number of larvae per plant increases
the earlier in development that the plant is infested
later in the season as the population builds
in sheltered areas near hedgerows, buildings, treelines
Swede midge are considered weak flyers and are easily blown into sheltered areas, where high winds do not interfere with finding mating partners and females finding suitable hosts to lay eggs.
Crucifers are susceptible to swede midge all season long

24. Swede Midge Life Cycle Eggs ~0.3 mm Soil Mating 1-5 days 3 days
Transparent to creamy white
2-50 eggs/cluster
100 eggs /female
Soil
Mating
1-5 days
3 days
moisture
drought
Adults ~1.5 to 2 mm
4-5 over-lapping generations
Larvae ~0.3 to 3-4 mm
Transparent on first hatch to yellow
when mature, feed gregariously at plant growing tip
21-44 days
per generation
Emerge
mid-May
7-21 days
7-14 days
Adults emerge in the spring in mid-May, give or take a week or so, depending on the weather conditions. Optimum conditions fro emergence, according to laboratory studies conducted by Shelton and Chen at Cornell, are 25 to 75% soil moisture with extremely dry or saturated conditions not being favorable for emergence. Swede midge mate within the same day they emerge and then the females lay 2-50 eggs per cluster up to 100 eggs per female in her short 1-4 day lifespan. After 3 days, larvae hatch and feed. During drought conditions, they have the capability to drop to the soil and remain dormant until optimum conditions (rainfall or irrigation) resume. They are very resilient to survive adverse weather conditions. After 7-21 days, larvae drop to the soil to pupate. The majority pupate within the top 1-2 cm (very shallow). Within 7-14 days, they emerge as adults. In New York and Ontario, there are 4-5 overlapping generations per season. The overwintering generation spins a cocoon, which can survive in the soil for more than 1 year. This is why swede midge can be very persistent once introduced to an area.
Pupae ~2-4 mm
most within top 2 cm of soil,
Optimum 25-75% soil moisture
for emergence
Overwintering
Cocoons
Survive in soil > 1 year
May-June
July
July-August
August
Sept - Oct
Pre-pupae

25. 2006 Swede Midge Trap Activity – Ontario, Canada
This chart illustrates swede midge trap catches of males in Ontario, Canada at three locations. Notice that the population tends to build with each generation as the season progresses. Also, note that peak flights occur at different times at different sites. Swede midge activity is very site specific. Note, there are always some SM present at all times.
J. Allen, M. Paibomesai and H. Fraser, 2006