A novel association between the grass pest Argentine stem weevil (Coleoptera: Curculionidae) and peas

Argentine stem weevil (Listronotus bonariensis), has been confirmed as infesting spring sown pea seedlings drilled in October 2016 on a Canterbury farm. Infestations occurred across two paddocks with 7-10% of the seedling estimated to be attacked in the worst affected areas. Symptoms included wilting and yellowing of new growth. Visual inspection of infested plants found entry and exit points, mining of the stem and a single larva per seedling. DNA amplification of the 5’ COI gene region of four larvae collected from individual plants provided a 100% match to L. bonariensis. The peas had been direct drilled into a nil-endophyte ryegrass (Lolium spp.) stand that had been treated with herbicide to kill the vegetation but not treated with insecticide. Listronotus bonariensis eggs were also found on one of the plants collected from the paddock on 18 November 2016. This is a new host plant record for L. bonariensis, and while considered a specific pest of grasses, adults will feed on seedling brassicas.