Whitefly Resistance Management: Time and Space Refugia in Cross-Commodity Systems of Arizona and California

Insecticides are central for control of whiteflies (Bemisia argentifolii = B. tabaci MEAM1); however, this pest has frequently evolved resistances. Chemical controls are available for whiteflies in Arizona and California’s cross-commodity agricultural communities. To curtail chemical resistances in whiteflies, resistance management programs are a necessary component of an Integrated Pest Management (IPM) plan. Diversifying practices and not over relying on available chemistries allows us to actively manage refugia. Available section-level application records of whitefly control chemistries from 2013-2017 were used in developing insights into local and regional usage patterns and the availability of temporal and spatial refuges to whitefly populations. Populations collected from cotton were tested for susceptibility to seven chemistries: acetamiprid, imidacloprid, buprofezin, cyantraniliprole, fenpropathrin, pyriproxyfen, and spiromesifen. Temporal and spatial refugia for six whitefly modes of action (MoA) were calculated over a region-wide and community level associated with collected populations. Mortality data were compared with pesticide usage patterns over five look-back periods preceding the date of collection. We produced validated partition models that predicted whitefly susceptibilities based on the availability of spatial or temporal refugia in ca. 23 sq km communities for each mode of action. In our analyses there were variations in model performance with some performing relatively well, while others did not. Further refinement may be needed to optimize look-back periods for better model performance. Insights gained should support development of practical decision tools that could be used by growers to better partition chemistry through space and time in their local communities