Baseline Susceptibility of Bemisia tabaci, Biotype B (Hemiptera: Aleyrodidae) to Chlorantraniliprole in Southern Florida

Chlorantraniliprole 200 mg ai L⁻¹ (Rynaxypyr® 200 SC) is the first xylem systemic insecticide in the new chemistry class, anthranilic diamides. A laboratory systemic bioassay using cut stems of cotton seedlings was developed to quantify the baseline susceptibility of the sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B, to chlorantraniliprole. Bioassays were conducted for a susceptible laboratory colony and for 11 field populations collected in 2008 and 2009 in Southern Florida. Baseline data of the susceptible colony (targeting first instar nymphs with initial exposure at the egg stage) for chlorantraniliprole in 2008 and 2009, revealed a pooled LC₅₀ and slope values of 0.033 mg ai L⁻¹ and 1.186, correspondingly. With the implementation of the stabilization period in the bioassay method in 2009, the susceptible colony generated LC₅₀ and slope values of 0.182 mg ai L⁻¹ and 0.972, respectively. LC₅₀ and slope values of field collected populations (targeting nymphs as above) ranged from 0.016 to 0.046 mg ai L⁻¹ and 0.889 to 1.595, respectively, in 2008 and 2009. Resistance ratio values at 50% mortality (RR₅₀) on nymphs of field colonies ranged from 0.496 to 1.377. LC₅₀ and slope values of the last 3 field collected populations of 2009, using the stabilization period, ranged from 0.117 to 0.251 mg ai L⁻¹ and 0.885 to 1.395, respectively, and RR₅₀ values ranging from 0.645 to 1.381. The overlapping of the fiducial limits of the LC₅₀ values, the low RR₅₀ values, and no significant differences in the slopes of the probit lines between the laboratory and field colonies, indicate that B. tabaci populations collected in Florida in 2008 and 2009 were highly susceptible to chlorantraniliprole. This anthranilic diamide insecticide is a promising tool in integrated pest management programs for B. tabaci, particularly where field populations have developed resistance to other insecticide groups. The baseline information developed in the present study confirmed the susceptibility of field populations in Florida and represents the basis for future susceptibility monitoring programs to help ensure the continued viability of chlorantraniliprole for B. tabaci management.