(2nd Place) Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) tolerance to Spirotetramat in south Florida tomato fields

One of the most destructive invasive pests worldwide is the sweetpotato whitefly, Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae). The Florida specialty crop market, worth billions of dollars, suffers major losses because of MEAM1 injury. Spirotetramat is frequently used by Florida specialty crop growers to control MEAM1 nymphs. A previous study based on maximum dose bioassays has indicated that MEAM1 populations in Florida may be developing tolerance to spirotetramat. The long-term efficacy of this active ingredient depends on the continued monitoring of MEAM1 population tolerance and the development of baseline susceptibility data. Fourteen populations of MEAM1 collected in south Florida were tested for tolerance to spirotetramat through nymphal serial dilution bioassays. The field populations responses were compared with a susceptible MEAM1 laboratory colony. LC50s and resistance ratios (RR) were quantified to determine tolerance levels. Our findings suggested variable MEAM1 tolerance to spirotetramat across south Florida. Among the populations tested, 12.5% remained relatively susceptible (2.94 – 4.11 RR) to spirotetramat. Low to moderate tolerance was found in 56% of the populations (15.98 – 58.09 RR). Over thirty percent of the populations tested were highly or extremely tolerant (126.16 – 794.88 RR). Overall, the variable efficacy of spirotetramat in some field populations suggests that tolerance to this insecticide might be developing in certain regions of south Florida. These results will be useful for improving recommendations for spirotetramat use in areas with moderate to extremely high tolerance.