SUSCEPTIBILITY OF DIFFERENT INSTARS OF THE OBLIQUEBANDED LEAFROLLER (LEPIDOPTERA, TORTRICIDAE) TO BACILLUS-THURINGIENSIS VAR KURSTAKI

Susceptibilty of different instars of the obliquebanded leafroller, Ch oristoneura rosaceana (Harris), to Bacillus thuringiensis Berliner var . kurstaki was determined in the laboratory by using a leaf dip bioass ay: All larval stages were susceptible to B. thuringiensis; fourth and sixth instars were the most and the least sensitive, respectively. A sublethal concentration of B. thuringiensis var. kurstaki had differen t effects on the development of surviving larvae, depending on the sta ge treated. Treated first instars weighed significantly less and lan a l development time was longer than the controls, but pupal weight and adult emergence were not affected. When fifth instars wt re treated, h owever, pupal weight and adult emergence were significantly reduced. T reatment with B. thuringiensis var kurstaki did not affect tile adult sex ratio of survivors in experiments with first or fifth instars.