Attractiveness of oilseed rape cultivars to Brassicogethes aeneus and Ceutorhynchus obstrictus as a potential control strategy

The abundances of two pests, pollen beetle (Brassicogethes aeneus (Fabricius, 1775)) and cabbage seed weevil (Ceutorhynchus obstrictus (Marsham, 1802)), were measured before flowering and in the full bloom of oilseed rape cultivars with different phenologies (two yellow-flowering: DK Exssence (the earliest), DK Sensei (the latest) and one white-flowering in time between yellow-flowering cultivars), and the differences in their abundance in the selected cultivars were determined in plot experiments during 2015–2018. No significant differences in pollen beetle and cabbage seed weevil occurrence were observed between the cultivars in the pre-flowering period, but during flowering, the two yellow-flowering cultivars were more attractive than the white-flowering cultivar for both pests. In the white-flowering cultivar, 57% and 69% reductions in the pollen beetle and cabbage seed weevil populations, respectively, were found relative to the two with yellow flowers. Thus, the use of white-flowering cultivar (less attractive, later flowering) as the main crop and the yellow-flowering cultivar (more attractive, earlier flowering) at field edges, with the width of the one-track line, could serve as a strategy to manage oilseed rape pests during flowering. This control strategy which combines more and less attractive oilseed rape cultivars may contribute to a reduction in the use of pesticides and their negative impact on the environment.

Differences in flight activity of pests on winter and spring oilseed rape

For 6 years the flight activity of pests on winter and spring oilseed rape was studied from spring till harvest, using yellow traps. In all years the flight intensity was higher in winter rape than in spring rape. The dominant insect pests of winter oilseed rape were Ceutorhynchus obstrictus, C. napi, C. pallidactylus, Dasineura brassicae, Meligethes aeneus, Phyllotreta atra and Ph. nigripes; subdominant were Athalia rosae, Brevicoryne brassicae and Psylliodes chrysocephala. In spring rape the dominant species were Brevicoryne brassicae, Ceutorhynchus obstrictus, Dasineura brassicae, Meligethes aeneus, Phyllotreta atra and Ph. nigripes; subdominant were Athalia rosae, Ceutorhynchus napi, C. pallidactylus and Psylliodes chrysocephala. Dasineura brassicae was not evaluated from trap catches. The damage by D. brassicae is higher to pods on axillary branches than on the main inflorescence. The occurrence of pests on spring rape was tied to a unsuitable phenophase of the plants at the time of flight activity and to the suitability of food. Winter rape requires a higher intensity of chemical treatment against pests than spring rape.

The parasitoid communities associated with an invasive canola pest, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), in Ontario and Quebec, Canada

Surveys were conducted to determine the parasitoid communities associated with the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), an important invasive pest of canola in Ontario and Quebec, Canada. More than 18 species of Chalcidoidea (Hymenoptera) were associated with this pest through mass rearings from canola siliques. In southwestern Ontario, the most abundant species were a species of Chlorocytus Graham (23.6%–48.6%), Lyrcus perdubius (Girault) (0%–53%), L. maculatus (Gahan) (2.8%–14.7%), and species of Pteromalus Swederus (0.6%–23.1%) (Pteromalidae). In contrast, the most abundant species in Quebec were Trichomalus lucidus (Walker) (Pteromalidae) (33.3%–56.4%), unidentified Eulophidae (2.1%–39.1%), Mesopolobus gemellus Baur and Muller (Pteromalidae) (1.3%–21.4%), and Necremnus tidius (Walker) (Eulophidae) (11.5%–19.3%). In the Ottawa, Ontario, area, parasitoids were first recovered in 2008, and Trichomalus perfectus (Walker) (Pteromalidae), M. gemellus, and species of Pteromalus were most prevalent. Mesopolobus gemellus and T. perfectus are reported in North America for the first time. Although existing communities appear to provide substantial parasitism (e.g., 6.3%–26.3% in 2006), species composition varies among years and differs from that in other regions in North America. Thus, parasitism levels and parasitoid communities of the cabbage seedpod weevil should be monitored to assess whether these will increase or there is a need to introduce more host-specific species from Europe that could provide greater mortality.

Larval phenologies and parasitoids of two seed-feeding weevils associated with hoary cress and shepherd's purse (Brassicaceae) in Europe

In Europe, Ceutorhynchus turbatus Schultze and Ceutorhynchus typhae (Herbst) (Coleoptera: Curculionidae) feed on seeds from hoary cress and shepherd's purse (Cardaria draba (L.) Desv. and Capsella bursa-pastoris (L.) Medik.); both plants are invasive in North America. In North America, C. turbatus is a candidate for biological control of hoary cress, C. typhae is adventive, and both are sympatric with cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham)), an invasive alien pest of canola (Brassica napus L. and Brassica rapa L., Brassicaceae). We investigated host associations among C. turbatus, C. typhae, and their parasitoids in Europe. Of particular interest was host specificity of Trichomalus perfectus (Walker) and Mesopolobus morys (Walker) (Hymenoptera: Pteromalidae), candidates for biological control of C. obstrictus in North America. We found no evidence that T. perfectus attacks C. turbatus or C. typhae; however, M. morys was the most common parasitoid associated with C. turbatus.