This thesis is an investigation of several aspects of diapause in the swede midge, Contarinia nasturtii (Kieffer). After developing methodology for induction and quantification of diapause entry in the laboratory, heritability of diapause entry was assessed for sibling larvae reared under diapause-inducing conditions. The diapause-quantification technique was efficient, but diapause frequencies were highly variable across studies employing similar diapause-inducing conditions. The diapause entry trait may be weakly heritable. A field study was conducted on diapause entry and emergence patterns. Diapause frequency was inversely correlated with photoperiod and absolute maximum air temperature. Photoperiod did not influence emergence timing. Two emergence phenotypes were observed before mid-July and a third minor emergence phenotype may exist in mid-to-late August. Approximately one third of emergence in the field was attributed to larvae in diapause for two or more years. Avenues of future research on diapause regulation in both the laboratory and field are discussed. / Natural Science and Engineering Research Council (CGS-M), Ontario Ministry of Agriculture, Food, and Rural Affairs (University of Guelph Sustainable Production Program)

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In Quebec, the swede midge (Contarinia nasturtii), a newly invasive pest, was found for the first time in 2003. During a two year study (2004-2005) I studied the seasonal development of the swede midge, the presence of natural enemies and tested entomopathogenic nematodes for its control. Results showed that the overwintering generation of the swede midge emerged during the second half of June. Based on adult captures and abundance of larvae in the field, there were three to four overlapping generations. Late transplants were more heavily attacked by the swede midge and broccoli and cauliflower were the most susceptible crops. No parasitoids were found in the experimental sites during either year of the study and two polyphagous coccinellid predators (Harmonia axyridis and Coccinella septempunctata) were field-collected for further evaluation under laboratory conditions. Although these two coccinellid species fed on swede midge larvae in plastic containers, further experiments demonstrated that H. axyridis was not able to prey on swede midge larvae on infested broccoli plants. The susceptibility of swede midge larvae to three species of entomopathogenic nematodes (Steinernema feltiae, S. carpocapsae, and Heterorhabditis bacteriophora) was also evaluated in laboratory assays. Heterorhabditis bacteriophora was the only species that caused significant mortality to swede midge larvae and, at a concentration of 1000 IJs/larva, caused 90-100% mortality in loam, sandy loam, clay and muck soil. This is the first study describing the seasonal development of the swede midge in Quebec. In addition, the potential use of entomopathogenic nematodes as biological control agents against the swede midge is demonstrated.

Monoculture agriculture has developed as a result of the Western agricultural growth model, which emphasizes reduced on-farm labor and maximum yield. As a result soil health, which is reliant on a diversity of soil-dwelling organisms, is compromised, pest problems are intensified, and biodiversity is lost when vast land areas are devoted to simplified vegetation schemes. There has been a tremendous rise in interest in alternative cropping schemes. The traditional practice of intercropping has received renewed interest as the emphasis on agricultural growth shifts from a purely development-based model to one of conservation and enhanced biodiversity. Although intercropping has shown promising results in controlling specialist herbivorous insects, how intercropping works is not known. Theories that explain the underlying mechanism of intercropping success include chemical repellency and physical masking. We tested these two theories by creating a simulated intercropping system in mesocosm cages in a laboratory environment. We tested twenty intercrops that varied in their vegetation type, size, and phylogenetic distance for their ability to repel an insect pest that recently invaded into North America, the swede midge (Contarinia nasturtii), from its host plant, Brassica oleracea. We found that different non-host plant treatments significantly influenced larval abundance, which indicates that C. nasturtii responded to some aspect of the varying plant combinations. We found that phylogenetic distance did not influence larval densities. Additionally, non-host plant height and leaf area of non-host plants did not influence larval densities. We found that vegetation type significantly affected larval densities. Brassica oleracea planted in combination with groundcover non-host plants had the fewest number of larvae, followed by B. oleracea planted in combination with vegetables. The highest number of larvae was found on B. oleracea plants planted in combination with herb non-host plants. Our research did not support a chemical repellency or visual masking theory of intercrop success.