LABORATORY EVALUATION OF 4 COMMERCIAL PREPARATIONS OF BACILLUS-THURINGIENSIS (BERLINER) AGAINST THE SPOTTED STEM BORER, CHILO-PARTELLUS (SWINHOE) (LEP, PYRALIDAE)

Commercial Bacillus thuringiensis formulations based on var. kurstaki (B.t.k.) (Thuricide(R), SAN-415(R), Dipel 2X(R)) and var. aizawai (Certan(R)) were bioassayed against second (L2), third (L3), fourth (L4) and fifth (L5) instar larvae of the stem borer, Chilo partellus, by incorporation into artificial diet. Dipel 2X(R) was the most toxic formulation tested against all larval instars. Certan(R) was non-toxic. The L2 was the most susceptible stage to all B.t.k. treatments, followed by L5 whilst the L3 and L4 were the most resistant. A Thuricide(R) treatment, administered at a sub-lethal dose level, reduced the rate of larval weight gain, increased larval mortality, lengthened the larval development period, reduced the rate of pupation and adult emergence and reduced the tunnelling capability in treated C. partellus larvae compared with untreated controls.