Investigating diapause and emergence phenotypes in the invasive species, Contarinia nasturtii

The swede midge (Contarinia nasturtii (Kieffer)) (Diptera: Cecidomyiidae) is an invasive pest of cruciferous crops in North America with high potential for economic impact. A new predictive model, MidgEmerge, was developed using DYMEX modelling software and used to investigate emergence phenotypes and diapause induction conditions in the swede midge. The MidgEmerge model indicates that diapause induction may be triggered by photoperiods £ 13.5 hrs during the larval stage. Observed spring emergence patterns of adults in southern Ontario, Canada, cannot be explained without the presence of multiple emergence phenotypes. MidgEmerge indicates that there are two emergence phenotypes of the swede midge, each completing four generations per year in southern Ontario. A fifth generation of each may become possible with climate change. Manipulation of various parameters indicates that the emergence phenotypes differ in diapause intensity rather than having different response thresholds to environmental parameters. The presence of multiple emergence phenotypes may act as a form of bet-hedging, allowing the population to prevail despite some emergence during adverse periods, and thus may contribute to the success of the swede midge as an invasive insect. MidgEmerge has the potential to be an important predictive tool to inform and direct integrated pest management practices targeted against swede midge in North America.