What is Swede Midge? | St. Lawrence University Sustainability Program

What is Swede Midge?

Monday, October 30, 2017

From a distanced eye, the row of storage kohlrabi looked sturdy and formidable, they were the biggest I had ever seen Yet, on closer inspection, some of these giants were hallow and damaged. It was obvious they had been in a fight, and lost: but to what? That was where I learned the term ‘Swede Midge’ and what inspired me to dedicate my first blog post to learning more about it.

Swede Midge, initially, I misperceived it to be a disease, but it is actually an invasive insect. Regarding its biology, the fly is very small (1.5-2 mm) and brown. Their lifespan is only up to five days, but in that time an adult female can lay 100 eggs. What is especially unfortunate is that the eggs are laid on the growing point of plants. Specifically, the swede midge flies infest crops of the brassicas family, such as broccoli, cauliflower, or in the case I encountered, kohlrabi. After the eggs are laid, it takes a few days for them to hatch into larvae which is where the majority of the damage to the host plant occurs. To consume the plant matter, the larvae produce a secretion that breaks down and liquefies its cell wall which causes the formation of leaf and flower galls, misshapen growing points, and other deformations. After 7-12 days, the larvae complete their development and drop into the soil to pupate and emerge weeks later as adults to restart their life cycle. Native to Europe and southwestern Asia; how did it get to small, rural Canton, New York? Well, it was first discovered in Canada and from their introduced in New York in the mid-2000s. Its distribution is somewhat limited then to New England, but also uniquely in Minnesota as well. The midge is able to fly for short distances, but it appears to spread easier through the soil. It is also able to go into dormancy during winter and in periods of drought. This suggests that since it is here now it will be here for good.

In reflection, this post was rather concerning (I keep scratching my head from thinking of bugs) but also informative of the realities that our garden ecosystem faces. In the future, I would like to compliment this piece by researching management strategies and possible ways to limit the amount of swede midge that is hurting the brassica crops like that fallen kolhrabi.

Resources used in the composition of this piece: