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.