Investigating the host plant range of <i>Contarinia nasturtii</i> (Diptera: Cecidomyiidae), reveals novel hosts and lack of host plant resistance within a <i>Brassica napus</i> diversity panel

Swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), is an invasive pest of canola (Brassica napus Linnaeus, Brassica juncea Linnaeus, Brassica rapa Linnaeus) and other Brassicaceae crops that causes significant damage in eastern North America. Contarinia nasturtii has the potential to invade the Canadian Prairies, which represents North America's largest canola growing region. This study examined host plant range, female oviposition preference, and larval development of C. nasturtii on selected weed, cultivated, and model Brassicaceae species. We also examined potential host plant resistance using a diverse panel of B. napus lines and developed a novel measure of larval performance using the proportion of third instar larvae as a proxy for larval development. All tested weed species, except Descurainia sophia Linnaeus, supported C. nasturtii development and 5 new host plants (Lepidium densiflorum Schrad., Neslia paniculata (Linnaeus) Desv., Diplotaxis muralis (Linnaeus) DC., Camelina sativa (Linnaeus) Crantz, and Erysimum cheiranthoides Linnaeus) were identified. Notably, we provide the first evidence that Arabidopsis thaliana Linnaeus can be a host for C. nasturtii, establishing a novel model system for gall midge-plant interaction studies. Evaluation of B. napus lines found slight variation in oviposition but no strong resistance, suggesting the need to investigate resistance sources outside of B. napus. These findings expand our knowledge on the host range of C. nasturtii, introduce A. thaliana as a tractable experimental model system, and underscore the need for investigation of host plant resistance and the development of integrated pest management strategies for C. nasturtii to mitigate threats to North American canola production.