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Ontario Grain Farmer Magazine

Surveying the population structure and resistance to pesticides in soybean two-spotted spider mite populations

Principal Investigator: Vojislava Grbic

Research Institution: Western University

Timeline: June 2021 – June 2026  

Objectives:

  • To develop and validate a diagnostic tool for detection of two-spotted spider mite (TSSM) pesticide resistance.
  • To test the susceptibility of TSSM populations collected from soybean fields to registered pesticides; in particular, to identify the frequency of dimethoate resistance in soybean mite populations that will determine the need for additional pesticide registration for mite control on soybean (already anticipated due to climate change).
  • To integrate project deliverables into GFO’s Pest Manager App and the Field Crop Protection Guide, OMAFRA Publication 812.
  • To develop recommendations for sustainable TSSM pest and resistance management to Ontario soybean growers based on evidence of pesticide susceptibility in the surveyed populations.

Impacts:

  • Farmers: Determination of the frequency of dimethoate resistance in soybean mite populations will inform farmers of the adequacy of this pesticide for mite control on soybean. If the resistance is frequent and widely distributed, there may be a need to register new pesticide(s) for mite control on soybean. The study will provide a list of pesticides to which mite populations are susceptible. The effective and pro-active pesticide resistance management for TSSM will contribute to the farmers’ ability to economically and efficiently control TSSM populations. This will result in increased crop security and greater revenues, as well as decreased overall costs of pesticides.
  • Integrated Pest Management (IPM) specialists: Identification of effective pesticides against TSSM populations and the ability to identify TSSM pesticide resistance will help to rule out application error, help growers make correct decisions regarding dimethoate use and increase the efficiency of IPM against this pest.
  • Environment: Efficient TSSM pest control will reduce unnecessary or multiple applications of pesticides that no longer effectively work, allowing farmers to use pesticides more economically and resulting in reduced environmental footprint of crop production.
  • Chemical industry: Efficient monitoring of TSSM pesticide resistance will increase pesticide efficacy, extending their utility and marketability, supporting greater revenues for companies and pesticide availability for farmers.

Scientific Summary:

The two-spotted spider mite (TSSM), Tetranychus urticae, is a global pest that feeds on more than 150 crops including soybean. In Ontario, it is an established pest on soybean. Integrated pest management (IPM) for TSSM involves monitoring the population and applying insecticides when thresholds are reached. TSSM pest pressure is especially high in dry years. With climate change, the TSSM pest pressure is expected to increase, predicting the need for the effective pesticide control of TSSM. Dimethoate (Lagon® or Cygon®), an organophosphate pesticide, is currently the only active ingredient registered for mite control on soybean. However, our pilot analysis identified mite resistance to dimethoate in all field TSSM populations tested, which correlates with dimethoate inefficiency reported by farmers. If alternative pesticides are to be registered for mite control, it is not clear which pesticides are expected to be effective, due to the multi-resistance status of most mite populations.

Surveying the pesticide resistance status of TSSM populations across soybean production areas in Ontario will inform the pesticide registration processes. It will determine the current state of efficacy of dimethoate for mite control and will identify the most effective alternative pesticide(s) that can be registered for TSSM control on soybean. In addition, soybean fields dominate the agricultural landscape in Ontario and represent the major reservoir of TSSM populations. Soybean fields surround more localized greenhouse and horticultural production where mites and their pesticide resistance are one of the major problems hindering production process. It is currently unclear where the founder populations infesting greenhouses and horticultural crops come from, and if they already carry resistance alleles. Additionally, if they do, what is the pattern of their pesticide resistance. Investigating the relatedness of TSSM populations from different production systems will identify potential mite migratory paths and will enable development of measures to eliminate or decrease mite spread.

External Funding Partners:

This work was supported by Mitacs through Mitacs Accelerate.