Abstract
One of the most destructive invasive pests worldwide is the whitefly, Bemisia tabaci MEAM1. The Florida vegetable crop market, worth millions of dollars annually, suffers major losses because of whitefly injury. Spirotetramat is frequently used by Florida vegetable crop growers to control whitefly nymphs. A previous study based on maximum dose bioassays indicated that MEAM1 populations in Florida may be developing resistance to spirotetramat. Thus, the long-term efficacy of this active ingredient depends on the development of baseline susceptibility data and the continued monitoring of MEAM1 populations' susceptibility. In the present study, 16 populations of whiteflies collected in south Florida were tested for resistance to spirotetramat through serial dilution bioassays designed to test whitefly nymphs. The field populations’ responses were compared with a susceptible MEAM1 laboratory colony. Median lethal concentrations (LC50) and resistance ratios (RRs) were quantified to determine MEAM1 resistance levels. Among the populations tested, 12.5% remained relatively susceptible (3–4 RR) to spirotetramat. Low to moderate resistance was found in 56% of the populations (16–58 RR). Over 30% of the populations tested were highly or extremely resistant (126–795 RR). Overall, the variable susceptibility of spirotetramat in some field populations indicates that resistance to this insecticide has developed in certain regions of south Florida. This is the first report of spirotetramat resistance in the United States. These results will directly refine management recommendations for spirotetramat use in areas where MEAM1 populations exhibit resistance.