Persistence of Bacillus thuringiensis in Two Formulations Applied by Helicopter Against the Western Spruce Budworm (Lepidoptera: Tortricidae) in North Central Oregon1

Abstract

Inactivation rates of Bacillus thuringiensis were determined for two formulations applied at 20 and 30 billion international units/ha by helicopter against the western spruce budworm, Choristoneura occidentalis Freeman. The number of days before spray residues declined to 50% of original activity varied with the dosage. Because inactivation rates of the four treatments were approximately equal, success of a B. thuringiensis control program apparently depends more on the initial rate of larval mortality than on the persistence of the microbial agent.