An ecological and genetic assessment of Colorado potato beetle insecticide resistance risk on Wisconsin organic potato farms

Commodities

Practices

This project, titled an ecological and genetic assessment of Colorado potato beetle (CPB) insecticide resistance risk on WI organic potato farms, investigates how insecticide resistance develops in CPB (Leptinotarsa decemlineata) populations across agricultural systems that are ecologically connected. Organic producers, with significantly fewer pest control options, are concerned that they will be adversely impacted by the emergence of insecticide resistance from nearby conventional production. This is a real concern, as CPB has been shown to evolve cross-resistance to insecticides, including organic insecticides. The study focuses on quantifying resistance to two commonly used insecticides-spinosad, approved for use in organic production, and imidacloprid, a neonicotinoid widely used in conventional systems-and identifying the ecological and genetic factors that drive resistance patterns. The proposed research explores four key questions: 1) What is the level of CPB resistance to spinosad and imidacloprid in organically and conventionally managed fields?, 2) Is there evidence of cross-resistance between these compounds in populations from organic fields?, 3) How does proximity to conventional production and potato intensity in surrounding landscapes relate to resistance levels on organically managed farms?, and 4) What gene expression patterns and networks are associated with CPB responses to spinosad and imidacloprid?

Building on previously collected data, CPB populations will be collected from organic and conventional farms across Wisconsin and tested for resistance to spinosad and imidacloprid. Insecticide bioassays will measure resistance levels, and a subset of larvae will be used for RNA-sequencing to identify genetic signatures associated with resistance. Landscape data will be used to evaluate how nearby potato production and proximity to conventional fields influence resistance patterns. Grower-focused surveys, and meetings will ensure results are shared directly with farmers, along with practical management recommendations. By integrating three years of bioassay (phenotypic) data, gene expression analysis, and farmer input, this project will support practical, sustainable approaches to CPB control across Wisconsin's potato industry.

This project will produce clear learning and action outcomes for organic potato farmers in Wisconsin, particularly those who have used spinosad over multiple years and whose fields vary in proximity to conventional production. Learning outcomes will include increased farmer understanding of how CPB resistance develops under repeated insecticide exposure and how landscape factors (number of years potatoes have been grown nearby or the distance to conventional fields) may influence resistance risk. Farmers will also become familiar with simplified summaries of probit regression results (LD50), evidence of cross-resistance to imidacloprid, and field-specific genetic data associated with resistance pathways.

Action outcomes may include changes in insecticide rotation practices, increased use of non-chemical control strategies, or improved attention to field layout and planting schedules. Participating growers may also report greater interest in collaborating with neighboring farms, regardless of management practices on addressing shared resistance pressures.

Furthermore, this project aims to support farmer confidence in managing CPB by providing data that is both specific to their fields and relevant to the broader region. By producing actionable resistance profiles, this project supports practical decision-making that strengthens long-term CPB control in Wisconsin's potato systems.