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Oviposition preference, larval distribution and impact of the swede midge, Contarinia nasturtii, on growth and yield of canola

Abstract

The swede midge (Contarinia nasturtii) has become a significant economic pest of canola (Brassica napus L.) in Ontario and an emergent pest in the Prairie provinces. Determining yield impacts of swede midge damage and the growth stage(s) at which canola is most vulnerable or attractive to swede midge will contribute to the development of pest management recommendations throughout the growth of the crop. In four experiments, canola plants were exposed to specific densities of adult swede midge and measures of oviposition, damage and yield were collected. There was a significant positive relationship between female density and total oviposition per plant with a very high capacity for larval numbers on canola; up to ~ 4000. Given a choice of four growth stages, approximately 85% of oviposition occurred on seven-leaf and early bud canola. Given no choice, the high total oviposition on 3-leaf and flowering stages suggests that swede midge will oviposit on less favorable canola growth stages, if no others are present. Damage sustained on primary racemes remained relatively constant over time. However, damage ratings on secondary and tertiary racemes decreased over time in the highest treatment densities, suggesting compensation by the plant. All yield measures, except seed weight per pod, significantly decreased with increasing female density on primary and/or secondary racemes. A density of ~ 0.6 females per plant resulted in 10% reductions in the number of pods and seed weight produced on primary racemes. These results support recommendations for insecticide applications at, or just prior to, the early bud stage.

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Acknowledgements

We are grateful for the assistance of H. Renkema, N. Daoust, A. Stinson, G. Davy, R. Simon and H. Zimmer in conducting these trials, and to L. Des Marteaux for use of her canola diagram. This study was supported by the OMAFRA-University of Guelph Sustainable Production Program (Plants), by the Ontario Canola Growers Association and by the Growing Forward 2 Program through the Eastern Canada Oilseeds Development Alliance and the Canola Council of Canada.

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Correspondence to Rebecca H. Hallett.

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Conflict of interest

RHH has received research service contracts and/or in-kind contributions of products from BASF Canada Inc., Bayer CropScience Inc., Dow AgroSciences, E.I. DuPont of Canada and Syngenta Canada Inc. JW has no conflict of interest to declare.

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Communicated by J. Gross.

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Williams, J.L., Hallett, R.H. Oviposition preference, larval distribution and impact of the swede midge, Contarinia nasturtii, on growth and yield of canola. J Pest Sci 91, 551–563 (2018). https://doi.org/10.1007/s10340-017-0940-2

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  • DOI: https://doi.org/10.1007/s10340-017-0940-2

Keywords

  • Diptera
  • Cecidomyiidae
  • Brassica napus
  • Oviposition preference
  • Density-dependent effects
  • Compensatory growth