Dongara weevil investigation update
The first season of the Dongara weevil surveillance program has concluded. This program is part of a 2 year Grains Research and Development Corporation (GRDC) and Department of Primary Industries and Regional Development (DPIRD) co-funded project. The project’s goal is to gain an understanding of the Dongara weevil’s host and environmental preferences to aid in the development of effective management strategies in the Geraldton port zone.
Researchers from DPIRD and the Mingenew Irwin Group set up pitfall traps at 20 sites in the Dongara and Mingenew areas to monitor for the presence of the weevil.
The team found that Dongara weevils were present in the soil in some paddocks prior to crop seeding, and the weevils remained throughout the season regardless of crop type. There was extensive damage reported on canola seedlings at crop emergence when weevils were present. Weevils did not appear to damage wheat, barley, or field pea crops. Some paddocks with weevil populations had implemented cereal rotations for several years prior to sowing canola.
Growers and researchers have only found weevils on soils with a high clay percentage, including self-mulching cracking clay, calcareous loamy earth, and grey-non-cracking clay. At all survey sites, crops experienced moisture stress for most of the season, due to low rainfall in 2023. The impact of rainfall on Dongara weevil populations is currently unknown. Researchers did not find weevil larvae this season, however, it is likely that they develop on crop roots.
Description and biology
Dongara weevils are tiny, approximately 3 to 5 mm long, dark brown to black in appearance and without prominent markings. They are smaller and darker than other weevils that commonly damage canola. Dongara weevils feed at night and are elusive during the day. During the day adult weevils cluster at the base of seedlings or under clods or in deep cracks in the soil. They have also been sighted sheltering at the base of wild radish and turnip weeds in some paddocks.
Dongara weevils have survived typical rates of insecticides used for common pests of canola. Research Scientist Dusty Severtson (DPIRD) suggested that weevils are using avoidance behaviour to evade synthetic pyrethroid and organophosphate foliar sprays. Preliminary laboratory tolerance testing has shown chlorpyrifos to be effective on weevils, bifenthrin to be somewhat effective, and fipronil and alphacypermethrin to have low efficacy.
Molecular analysis has shown that the Dongara weevil forms a separate species to all other pest weevils currently known worldwide. Weevil taxonomy specialists have suggested that only about a third of all weevils are known and named.
If you are unsure of the type of weevil you have found in your crop use the PestFacts WA Reporter app to request an identification by our entomologists.
Seeking volunteers for 2024 surveillance
If any growers in the Dongara and Mingenew region are interested in providing locations for the 2024 pitfall trap surveillance program, please contact DPIRD Research Scientist Christiaan Valentine on +61 (0)8 9699 2197. Pitfall trapping involves placing ten 500 mL containers into the soil near the paddock edge during the cropping season. At each site, DPIRD researchers will collect soil samples for a comprehensive soil analysis.
To read about earlier Dongara weevil activity this season, refer to the 2023 PestFacts WA Issue 8 article The unknown “Dongara” weevil has been attacking canola.
For more information contact Research scientist Christiaan Valentine, Northam on +61 (0)8 9690 2197.
Article author: Bec Severtson (DPIRD Northam).