Diagnostic Dose Assays for the Detection and Monitoring of Resistance in Adults From Listronotus maculicollis (Coleoptera: Curculionidae) Populations.

The annual bluegrass weevil, Listronotus maculicollis (Kirby) (Coleoptera: Curculionidae), is the most difficult to control insect pest on golf courses in eastern North America. Insecticide resistance, particularly to pyrethroids, is a serious and expanding issue in its management. Optimal diagnostic tools for resistance detection are crucial for efficient resistance monitoring and mitigation. Developed vial and Petri dish assays clearly separated different resistance levels among weevil populations. With the pyrethroid bifenthrin, susceptible, moderately resistant (resistance ratios, RR50s 12.2-95.7), and highly resistant (RR50s 258.2-1760.9) populations were distinguished. With the organophosphate chlorpyrifos, susceptible, tolerant (RR50s 2.4-6.7), and resistant (RR50s 8.8-120.7) populations were distinguished. In validation assays, several bifenthrin and chlorpyrifos concentrations were needed to separate resistance levels in Petri dish (bifenthrin: 112.2 and 336.3 or 3,362.5 mg AI/m2; chlorpyrifos: 3.4 and 33.6 mg AI/m2) and vial (bifenthrin: 112.1 or 1,120.8 mg AI/m2; chlorpyrifos: 2.2 and 11.2 mg AI/m2) assays. The Petri dish assay with formulated bifenthrin and chlorpyrifos was the best option for L. maculicollis resistance detection and monitoring. It demonstrated sufficient discriminating power, accurately reflected resistance levels, and was easier to conduct. A single diagnostic concentration sufficed to separate susceptible and resistant populations. To determine different resistance or tolerance levels, two to three concentrations were necessary.