Swede Midge Introduction, Damage and BiologyCornell Cooperative ExtensionChristy HoeptingCornell Cooperative Extension Vegetable Program
Swede MidgeSerious insect pest of cruciferous plants:vegetables (i.e. broccoli, cauliflower, Brussels sprouts, cabbage, collards, swede/turnip, Asian vegetables (i.e. bok choy, etc.)canolaweeds (i.e. shepherds purse, wild mustard)Ornamental crucifersCommon and endemic in Europe:Known since late 1800sMajor pest in Belgium, Germany, Switzerland, Netherlands, France, Poland and Slovania
Swede Midge in North America2000: 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% lossesEspecially in organic and small-scale operations
Swede Midge: Adult Adult femaleAdult male
Length: 0.3 mmWidth: 0.08 mmSwede midge: eggsDeep in the youngest actively growing vegetative tissue
Swede midge: larvae0.3 to 3-4 mm
Damage: Blind head, brown scarring at growing pointbroccoli
Damage: Leaf puckeringGreen cabbage
Damage: Leaf puckeringbroccoli
Damage: Leaf puckeringRed cabbage
Damage: Leaf puckeringcauliflower
Damage: Multiple shoots, growing pointsbroccoli
Damage: Multiple small headsRed cabbage
Damage: Brown corky scarring in headcauliflower
Damage: Brown corky scarring in headbroccoli
Damage: Brown corky scarring in headGreen cabbage
Damage: Secondary soft rot
Swede midge larvae in an infested growing tip
Damage: Swollen Flower Buds
Damage: Swollen Floretsbroccoli
Swede midge damage in canola
Field pennycressSwede midge damage on weeds
Swede Midge Damage SeverityIncreasesas number of larvae per plant increasesthe earlier in development that the plant is infestedlater in the season as the population buildsin sheltered areas near hedgerows, buildings, treelinesCrucifers are susceptible to swede midge all season long
Swede Midge Life CycleEggs ~0.3 mmTransparent to creamy white2-50 eggs/cluster100 eggs /femaleLarvae ~0.3 to 3-4 mmTransparent on first hatch to yellowwhen mature, feed gregariously at plant growing tipPupae ~2-4 mmmost within top 2 cm of soil,Optimum 25-75% soil moisture for emergencePre-pupaeAdults ~1.5 to 2 mm 4-5 over-lapping generationsOverwintering CocoonsSurvive in soil > 1 yearMating1-5 daysSoil3 daysdroughtmoistureMay-JuneJulyJuly-AugustAugustSept - OctEmergemid-May7-21 days7-14 days21-44 daysper generation
J. Allen, M. Paibomesai and H. Fraser, 20062006 Swede Midge Trap Activity Ontario, Canada
Chart2
211945
85113
600
1023.1111111111
00139
8029
34116
27422
8039
040
3226
26093
1960234
922333
109364
47774
40342
493320
315341.250
303230
803010
1997721
43520
5020
8300
230
Wellington Cty
Hamilton/Wentworth Cty
Simcoe Cty
Total # SM Captured on 3 Traps
Sheet1
Sheet1
211945
85113
600
1023.1111111111
00139
8029
34116
27422
8039
040
3226
26093
1960234
922333
109364
47774
40342
493320
315341.250
303230
803010
1997721
43520
5020
8300
230
Wellington Cty
Hamilton/Wentworth Cty
Simcoe Cty
Total # SM Captured on 3 Traps
Sheet2
Sheet3
***Swede midge is a tiny fly, less than 2 mm in size, which is difficult to distinguish from other midges except by a specialist.*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.*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.********Brown corky scarring is not limited to the growing points and leaf petioles, but can also cause damage in the heads of cauliflower****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.*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!*Another place to find swede midge larvae are in swollen florets in broccoli for example. Peel them open and you might find SM larvae.*Canola is another host for swede midge. Affect on yield depend on the stage of canola when it becomes infested.*Example of weed infested with swede midge, see the swollen leaf petioles.*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.*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. *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.