Sublethal effects of Bacillus thuringiensis on Plutella xylostella populations

The objective of this study was to investigate the sublethal effects of Bacillus thuringiensis on 4 populations of Plutella xylostella. Ten isolates of B. thuringiensis were used at 3 × 10⁸ spores/mL, and the products Btt090^®, Dipel^®, Agree^®, and Xentari^® were used at recommended doses. Suspensions of B. thuringiensis were used on kale leaf discs, and the control was water and 0.05% Tween 20^®. 100 second instar larvae of 4 populations were used per treatment. Larval viability, pupal viability, and larval period were evaluated. The only isolate that showed a significant difference among the populations was 20.7L; lower larval viability was observed in PJ (46%) population and higher larval viability in PA (78%) and PC (86%) populations. Agree^®, Dipel^®, Xentari^®, 49.19A, E47 and HD1 caused 100% mortality in all populations. 20.7L and T08.024 increased larval period in PA (8.80 and 8.73 days, respectively) and PJ (8.83 and 9.33 days, respectively), E7 induced a longer larval period in PA (8.76 days). T08.024 lengthened larval period in PJ (9.33 days) and 153.30A, 20.7L and Btt090^® in PC (7.91, 7.96, and 8.26 days, respectively). 20.7L and T08.024 affected pupal viability in PX (60.2%) and PC (19.4%), respectively. E28 decreased pupal viability in PX (38.3%), and T08.024 reduced pupal viability in PJ (46.1%) and PC (19.4%). Generally, 20.7L affected all populations, and T08.024 affected PA, PC, and PJ. This showed that these isolates were effective in management of different populations of P. xylostella.