Abstract
AbstractCommercial Bacillus thuringiensis var. kurstaki (B.t.k.) (Dipel 132® and Thuricide 48 LV®) were bioassayed at 20 and 25°C against 3rd- (L3), 4th- (L4), 5th- (L5), and 6th- (L6) instar larvae of the bertha armyworm, Mamestra configurata Walker, on greenhouse-grown canola, Brassica napus L. cv. Westar. The L4 was the most susceptible stage to B.t.k. but it was much less susceptible than the spruce budworm, Choristoneura fumiferana (Clem.), a species against which this bacterium is currently used. The lethal time of B.t.k. to the larvae was inversely related to dosage applied. Younger instars (L3 to L4) were more sensitive to Dipel than older instars (L5 to L6) at 20°C but the reverse was true for Thuricide-treated larvae. All B.t.k. treatments reduced weight gain and frass deposition (by inference feeding activity) compared with untreated controls. The LC50 concentration of B.t.k. for larvae reduced survival to adult emergence by 87–100%.
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