MORTALITY OF APPLE LEAFROLLER EXPOSED TO DIFFERENT Bacillus thuringiensis SUBSPECIES IN ARTIFICIAL DIET, IN THREE ASSESSMENT PERIODS

ABSTRACT Bioinsecticides based on Bacillus thuringiensis are the entomopathogen most marketed worldwide. The aim of this study was to evaluate the bioactivity of kurstaki, aizawai subspecies and kurstaki x aizawai hybrid on B. salubricola larvae fed on artificial diet in different assessment periods. Mortality was assessed on the seventh, tenth and fifteenth days after treatment. Microplates containing 150 µl of diet in each cell were used. Suspensions containing Bt subspecies was deposited on the surface of the diet, then neonate larvae were released. The mortality assessment performed after fifteen days of treatment was significant for all three subspecies. Bt kurstaki was more efficient in all assessment periods, except for fifteen days, which was similar to Bt aizawai. Assessments performed up to seven days were more efficient to determine mortality. The three subspecies have influenced the ability for instar change, regardless of concentration. The LC50 of Bt kurstaki on the seventh and tenth days of assessment was from three to six times smaller than that observed in Bt aizawai x kurstaki, and Bt aizawai, respectively.