The canola flower midge, Contarinia brassicola, is a recently discovered insect pest of canola widespread across the Prairies. Damage results when larvae feed on developing flower buds which prevents the flowers from opening and forming pods. The population density of canola flower midge is difficult to evaluate as densities are variable across the species range and damage is discreet and can be easily overlooked except under outbreak conditions.

Previous work identified the female-produced canola flower midge pheromone and optimized the pheromone blend and dose to create a potent male attractant. This project refined the pheromone trapping system and evaluated the relationship between adult midges captured in pheromone-baited traps and damage in the field. It also explored weather conditions that might influence populations, and the midges’ ability to infest canola at different growth stages and alternative hosts.

Field studies were carried out in commercial canola production fields in central Alberta in 2021 and 2022. Experiments took place over the growing season. In the lab, emergence of midge were monitored to determine if males and females emerge in equal numbers and their lifespan.  Of note, 2021 was an extreme drought and many fields had poor yields.

An optimized trapping system consisting of pheromone-baited Jackson trap, deployed 50 cm above the soil surface along the crop edge, was identified as the optimal combination of trap type and position to effectively monitor the canola flower midge. Two daily peaks in male midge activity were observed that could be used to increase the precision of monitoring strategies or potential treatment applications. Over the two years of this study (2021-2022), the number of male midges captured on pheromone-baited traps was not predictive of damage in the field and average air temperature and weekly cumulative rainfall, at the scale measured in this study, did not have an impact on the number of midges captured in either year. Midge larvae were identified from pods in commercial canola fields and experiments also confirmed canola flower midge larvae can develop in pods, but no alternative host plants were identified. Although short-lived, the midge emergence is prolonged over the summer when canola plants are susceptible to infestations, and we urge continued monitoring and vigilance for this species as its full pest potential is yet to be determined.

This project developed a reliable, pheromone-trapping system to monitor Contarinia brassicola (canola flower midge). Midge damage is more prevalent at the field edges compared to the interior, and larvae can occasionally be found in pods later in the season