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.

Spotted-wing drosophila (Drosophila suzukii (Matsumura) (Diptera: Drosophilidae)) is a pest of tender fruit and berry crops because female flies oviposit in ripening fruit. Frequent insecticide applications are needed for control during fruit ripening, with few noninsecticide options available. The effect of interplanting peppermint (Mentha × piperita Linnaeus (Lamiaceae)) in strawberry (Fragaria × ananassa Duchesne (Rosaceae)) on D. suzukii fruit infestation was investigated because peppermint essential oil deterred D. suzukii from fruit in the laboratory, and interplanted aromatic plants reduced crop pest populations in other field studies. Regardless of whether peppermint was untrimmed or periodically trimmed to reduce shading of strawberries and promote release of volatiles, D. suzukii infestation was consistently lowest in strawberries adjacent to no peppermint. Interplanted peppermint also reduced strawberry yield in the second year of the experiment. Abundance of Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), a strawberry pest, was higher in plots with peppermint, but abundances of Ligyrocoris diffusus (Uhler) (Hemiptera: Rhyparochromidae) and Neortholomus scolopax (Say) (Hemiptera: Lygaeidae), seed feeders but not common strawberry pests, were lower in plots with peppermint. Overall, interplanted peppermint is not recommended for D. suzukii management, but other strategies for using volatile, repellent compounds in the field should be investigated.

Swede midge (Contarinia nasturtii (Kieffer); Diptera: Cecidomyiidae) is a serious invasive pest of Brassica Linnaeus (Brassicaceae) oilseed and vegetable crops in Canada and the United States of America. Pheromone mating disruption is a promising new tactic for managing this difficult pest, but research is needed to determine how pheromone delivery can be optimised. With an understanding of swede midge diel mating patterns, pest managers could limit pheromone release to periods when midges are sexually active. We conducted a series of 24-hour trials to test whether swede midge exhibit diel periodicity of emergence, female calling, and male capture in pheromone traps. We found that females began releasing pheromones almost immediately following emergence within the first five hours after dawn. In the field, we found that males were most active from dawn until late morning, indicating that midges mate primarily during the first five hours of photophase. Low levels of reproductive activity during midday and nighttime hours present opportunities to turn off dispensers and reduce the cost of pheromone inputs in a swede midge mating disruption system.

Larvae of the swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), rely on environmental cues to initiate the diapause programme. This facultative diapause strategy, which provides opportunities for both bet hedging and multivoltinism, likely contributed to the successful colonisation and spread of this invasive pest in North America. Population diapause incidence is variable even under relatively stable conditions (especially at the critical day length), yet the mechanisms influencing the developmental trajectory of individuals under such conditions are unknown. Here we approach the non-environmental (i.e., heritable) controls of this variation by comparing diapause frequencies within and among full-sibling swede midge families reared in one of two stable environments. Under warm, long-day conditions > 99% of swede midges pupated directly, while 86% of swede midges entered diapause under cool, short-day conditions. In the latter condition, most families exhibited mixed developmental trajectories (ranging from 36% to 96% diapause). This developmental variation among siblings indicates that the diapause induction threshold does not follow simple Mendelian inheritance with complete dominance for a particular allele, but may follow incomplete dominance or a more complex heredity. Alternatively, within-family diapause variation may result from maternal bet hedging or factors such as maternal age or larval nutrition.

To determine resistance of Brassicaceae field crops to Contarinia Róndani (Diptera: Cecidomyiidae) midge complex (Contarinia nasturtii Kieffer and Contarinia undescribed species), field trials of two different host assemblages were undertaken near Melfort, Saskatchewan, Canada in 2014 and repeated in 2015. In both years the first midge adults appeared in early July, when most plants were starting to flower, and a second generation occurred in mid-August, past the period of crop susceptibility. In a trial studying 18 lines of six brassicaceous species, the lowest probability of midge injury was found on Camelina sativa (Linnaeus) Crantz lines in both years. No differences were found in the probability of midge injury among any of the 13 Brassica Linnaeus species lines tested, including commercial glyphosate-resistant and glufosinate-resistant Brassica napus Linnaeus canola lines, Ethiopian mustard (Brassica carinata Braun), brown or oriental mustard (Brassica juncea (Linnaeus) Czernajew), or Polish canola (Brassica rapa Linnaeus) lines. Probability of midge injury on Sinapis alba Linnaeus yellow mustard lines reached levels between those on Camelina sativa lines and those on Brassica lines. A second trial examining 14 current commercial glyphosate-resistant Brassica napus canola cultivars found no differences in susceptibility to midge feeding among any cultivars tested. More plants were damaged in 2015 in both studies, and damage reached maximum levels earlier in 2015 than in 2014.

Induction of diapause under laboratory conditions is a valuable tool for the study of dormancy in economic pests such as the swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae). In the present study, diapause in larval swede midge was achieved via manipulation of rearing photoperiod and temperature. Frequency of diapause was assessed by sieve separation of diapause cocoons from pre-sifted peat substrate following emergence of pupating individuals. Mean diapause frequency for swede midge larvae reared under cool conditions with short day length or cool conditions with decreasing day lengths were 45.2% and 19.5%, respectively. Only 1.2% of swede midge reared under warm, long day length conditions entered diapause. A small percentage of larvae neither pupated nor entered diapause and remained in substrate long after other individuals had emerged as adults. This behaviour was more prevalent under cool and short or decreasing day length rearing conditions. Approximately 76% of the larvae used for diapause induction were recovered with the present larval and cocoon retrieval method, and premature (larval and pupal) mortality averaged 18.2%. Although diapause occurred in the present study, conditions resulting in higher diapause frequencies should be investigated and attempts should be made to improve survival and recovery of individuals.

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.

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.