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Biotype B of the sweetpotato whitefly (SPWF), Bemisia tabaci (Gennadius) (also known as the silverleaf whitefly, B. argentifolii Bellows & Perring), is the key pest of tomatoes in south Florida, primarily as a vector of the begomovirus Tomato yellow leaf curl virus (TYLCV). Insecticides are most often used to manage the SPWF and TYLCV. A resistance monitoring program that was initiated in Florida in 2000 was continued from 2008 to 2010 and included 4 neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran, and acetamiprid), the insect growth regulator buprofezin, the pyrethroid bifenthrin, and the organochlorine endosulfan. Ten field populations in 2008 and 9 each in 2009 and 2010 were established with nymphal infested foliage and were tested for susceptibility using a systemic uptake, cut-leaf petiole bioassay with adults for the neonicotinoids; a leaf-dip bioassay with 2nd instars for buprofezin; and a vial bioassay with adults for bifenthrin and endosulfan. Each field population was exposed to the LC50 and LC95 of a known susceptible laboratory colony for each respective insecticide and mortality was compared with that at the same doses predicted from probit analyses of field populations tested in 2007. T-tests were used to determine the significance of differences between the mean mortality at the LC values of each field collected colony compared to the respective LC values of the laboratory susceptible strain. T-tests were also used to determine the significance of differences between the mean of the predicted mortality at the LC values of field collected populations in 2007 and the means of the LC values of field collected populations in 2008-2010 for each insecticide. Results indicated that, based on mortality averaged over all populations evaluated, all of the neonicotinoids indicated decreases in average susceptibility in 2008 and 2009 compared with the 2007 values, although the differences were less for dinotefuran and acetamiprid. The lowest average of mortality at both the LC50 and LC95 in 2008 and 2009 occurred for imidacloprid and thiamethoxam. These neonicotinoids had been in use longer than either of the other two. Mortality values for bifenthrin suggested an overall increase in field susceptibility in 2008 and 2009 while values for endosulfan suggested no change. There were no data predicted for buprofezin in 2007, but the 2008 average mortalities at the LC50 and LC95 were 0.438 and 0.802, respectively, indicating that field susceptibility was at an acceptable level. In 2010 the average susceptibility to the neonicotinoids appeared to have increased compared with previous years; however, the field populations tended to be evaluated after they had been reared in the laboratory without exposure to insecticides for more generations than in previous years. Despite this, average susceptibility to endosulfan appeared to decrease. The results showed the utility of using predicted LC50 and LC95 values, over the use of full dose range, for monitoring changes in susceptibility in field populations thru time. The data presented here provide important information aid to growers and producers in making decisions on insecticide usage. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]