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

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

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

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.

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

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.

Damage: Blind head, brown scarring at growing point broccoli

Damage: Leaf puckering Green cabbage

Damage: Leaf puckering broccoli

Damage: Leaf puckering Red cabbage

Damage: Leaf puckering cauliflower

Damage: Multiple shoots, growing points broccoli

Damage: Multiple small heads Red cabbage

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

Damage: Brown corky scarring in head broccoli

Damage: Brown corky scarring in head Green cabbage

Damage: Secondary soft rot

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.

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!

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

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.

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

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

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

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