In 1996, damage symptoms typical of the swede midge, Contarinia nasturtii (Keiffer), were observed on broccoli, Brassica oleracea L. var. italica (Brassicaceae), crops east of Toronto, Ontario. Early attempts to identify an associated insect larva were unsuccessful, and damage symptoms became mistakenly attributed to nutrient deficiencies (T Clarke, personal communication). Between 1996 and 1999, damaged plants were seen by growers regularly, and resulted in up to 85% loss of marketable yield (T Clarke, personal communication). In June 2000, we initiated investigations at two sites 12 km apart to determine the causal organism of this damage. Both sites were located at farms where cole crops are primarily -gown and from where the first damage reports originated.

A new species, Contarinia brassicola Sinclair (Diptera: Cecidomyiidae), which induces flower galls on canola (Brassica napus Linnaeus and Brassica rapa Linnaeus (Brassicaceae)), is described from Saskatchewan and Alberta, Canada. Larvae develop in the flowers of canola, which causes swelling and prevents opening, pod formation, and seed set. Mature larvae exit the galls, fall to the soil, and form cocoons. Depending on conditions, larvae will either pupate and eclose in the same calendar year or enter facultative diapause and emerge the following year. At least two generations of C. brassicola occur each year. Adults emerge from overwintering cocoons in the spring and lay eggs on developing canola flower buds. The galls produced by C. brassicola were previously attributed to the swede midge, Contarinia nasturtii (Kieffer) in Saskatchewan; here, we compare and list several characters to differentiate the two species.

In 2002, two types of light traps were compared against sticky yellow cards for efficiency and selectivity in capturing adult swede midge Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae). Incandescent light traps were more efficient at capturing swede midge than were sticky traps. Incandescent light traps were more selective than blacklight traps and required less time for processing of samples and identification of captured midges. Emergence (2003 and 2004) and pheromone (2004) traps were used to assess swede midge population dynamics. Captures from emergence traps indicate up to five overlapping emergence events for swede midge each year. Emergence traps captured swede midge earlier in the season than pheromone traps, but pheromone-trap captures continued later in the season than those in emergence traps. Pheromone traps are small and portable, easy to maintain, and capture significantly more swede midge than emergence traps.

BACKGROUND: Pheromone-mediated mating disruption, which uses large amounts of synthetic female pheromones to interrupt insect reproductive behavior, has been successful for managing important agricultural pests. While multiple mechanisms have been discovered explaining how synthetic pheromone treatments prevent males from finding females, it is less clear how unnaturally large doses of synthetic sex pheromone impact the behavior of female insects, particularly nonlepidopteran females. In some species, 'autodetecting' females possess pheromone receptors and respond to ambient pheromones by altering their mating behavior. Here, we test whether exposure to stereospecific and racemic synthetic pheromones influences calling and subsequent propensity to mate in female swede midge (Contarinia nasturtii Kieffer; Diptera: Cecidomyiidae), a pest of Brassica crops. RESULTS: In both laboratory and field settings, females exposed to stereospecific and racemic three-component pheromone blends called significantly more frequently and for longer durations than midges in control treatments. In the field, midges were twice as likely to call in pheromone-treated plots versus nontreated plots. Additionally, pheromone pre-exposure reduced subsequent mating: while 68% of female midges mated following control conditions, only 42% and 35% of females preexposed to stereospecific and racemic three-component blends mated, respectively. CONCLUSION: While more frequent calling within pheromone-treated backgrounds may increase the likelihood that females are detected by males, a reduction in female propensity to mate would increase the efficacy of a pheromone-mediated mating disruption system. Our work presents the first known investigation of autodetection behavior in Cecidomyiidae. Additional research is necessary to understand the implications of female autodetection for swede midge management.

Swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), causes severe economic losses in Brassica Linnaeus (Brassicaceae) crops in its invasive range in North America. Larvae feed within the meristem of their host plants, causing deformed heads, stems, and leaves. Pheromone-mediated mating disruption is particularly promising for swede midge management in high-value vegetable crops because its use is allowed in organic production. However, a major challenge to developing economically viable mating disruption is that the stereospecific three-component swede midge pheromone is costly to synthesise. In broccoli (Brassica oleracea Linnaeus var. italica) field plots, we tested whether stereospecific, lower-cost racemic, and single-component pheromone blends resulted in trap shutdown and reduced crop damage compared to nontreated controls. We found a significant reduction in males caught in three-component stereospecific and racemic pheromone–treated plots but not in the single-component treatments. Although marketable broccoli yields were not higher overall in the pheromone-treated plots compared with those in the controls, yields were significantly higher in the three-component stereospecific treatment in year 2. Therefore, the three-component stereospecific blend shows promise as a pheromone blend for swede midge mating disruption. However, due to high cost and levels of crop damage across all treatments, additional research is necessary to optimise swede midge mating disruption.