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Bug of the Month June 2019


Canola Flower Midge

Canola flower midge

By Boyd A. Mori, PhD
Research Scientist Agriculture and Agri-Food Canada
Saskatoon Research and Development Centre

Word Alert
Botany noun, plural: racemes
A flower cluster with the separate flowers attached by short equal stalks at equal distances along a central stem. The flowers at the base of the central stem develop first.

Bottle-shaped galled flowers along the raceme

Canola growers need to watch for a new pest this season. Researchers recently identified a new insect species feeding on canola throughout the Prairie Provinces. The new species, called the canola flower midge, Contarinia brassicola, appears similar to the swede midge, Contarinia nasturtii, commonly found in Ontario. The adult is a small, delicate fly, 2-5 mm in size (Picture 1). The females lay eggs on the developing canola buds. Upon hatching the larvae feed within the developing flower creating a “bottle”-shaped gall which prevents the flower from opening (Picture 2). This is the only damage symptom associated with the midge.

Surveys conducted by Agriculture and Agri-Food Canada, Alberta Agriculture and Forestry, and Canola Council staff identified damage throughout central Alberta, Saskatchewan and Manitoba. It has not been positively identified in Alberta south of Red Deer. Finding damage is often difficult, and producers are recommended to scout their fields in mid- to late-July after the majority of the crop has flowered. When scouting, you should observe 10 racemes from 10 locations along the field edge. Examine each raceme for unopened flowers in between elongating pods, these flowers can be opened and examined for small, yellowish-white larvae (Picture 3).

Larvae in opened flower gall

If larvae are not present, damage may be present as small, black feeding scars on the pistil of the flower. Two parasitoid wasps have been identified attacking the canola flower midge and most likely play a role in regulating midge populations.

Damage appears very low, often only a single damaged flower in 100 racemes, across the range of the canola flower midge. Research is underway to determine the midges full impact.