Comparison of Slide Dip and Petri Dish Assays for Measuring Resistance to Permethrin in Amblyseius fallacis (Acari: Phytoseiidae)

Abstract

The relative toxicity of permethrin to gravid female phytoseiid mites, Amblyseius Fallacies (Garman), was compared by slide dip and petri dish techniques, using two populations (P8, GBI) collected from Ontario apple orchards with different histories of pyrethroid use. By the slide dip assay, concentration-mortality regressions for both populations were linear with similar slopes. The LCso value was 5.5 ppm for P8 and 46.6 ppm for GBI. The latter is higher than any recorded in the literature from a commercial orchard. With the petri dish assay, the concentration-mortality regression for population P8 was linear and the LC50 was 2.3 ppm. In contrast, the regression for GBI was nonlinear and typical of a mixed population; 66% were similar to the susceptible P8 population but 33% were a more resistant population. The LC50 of the GBI population was 12.7ppm using the petri dish assay. The GBI, P8, and six other populations of A. fallacis from apple orchards were compared using the petri dish assay at two discriminating concentrations of permethrin to designate susceptible and resistant populations for genetic improvement to permethrin. Mortality at 20 and 80 ppm varied between 53–97% and 73–100%, respectively, for the eight populations and was related to the history of pyrethroid use in the orchards.