Sublethal effects of Bacillus thuringiensis on the reproductive performance of Plutella xylostella populations

The objective of this study was investigating the effects of Bacillus thuringiensis on reproductive performance of Plutella xylostella. Ten isolates were used at 3 × 10⁸ spores/mL, and the products Btt090^®, Dipel^®, Agree^®, and Xentari^® were used at the recommended doses. Suspensions of bacteria were used on kale leaf discs, and the control used was water and 0.05% Tween^® 20. The discs were offered to second instar larvae of 4 populations; a total of 100 larvae per treatment. Sex ratio, longevity, fecundity, incubation period, and egg viability of P. xylostella were evaluated. A higher sex ratio was observed in the PJ (0.5) and PA (0.6) populations with isolates 20.7L and T08.024. In PC population, the lowest sex ratio value (0.1) was observed with T08.024 treatment. Longevity decreased in the PX population (6.8 days) when T08.024 was used. Fecundity was significantly different among populations, and the PC and PX populations were negatively affected by treatment with Btt090^® (13.6 eggs/female) and T08.024 (12.5 eggs/female). Among the products/isolates tested on the same population, T08.024 and E28 caused lower fecundity in the PX (12.5 eggs/female) and PJ (14.0 eggs/female) populations, respectively. Incubation period and egg viability showed no significant difference among populations and products/isolates. The isolated T08.024 negatively affected PX and PC populations in a greater intensity than other isolates/products. Effects of the products/isolates on populations of P. xylostella were different. Therefore, the population and region of occurrence of the pest must be considered before using a control strategy.