PERSISTENCE OF BACILLUS-THURINGIENSIS IN 2 FORMULATIONS APPLIED BY HELICOPTER AGAINST THE WESTERN SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE) IN NORTH CENTRAL OREGON

Inactivation rates of Bacillus thuringiensus were determined for two formulations applied at 20 and 30 billion international units/ha by helicopter against the western spruce budworm, Choristoneura occidentalis Freeman [Oregon, USA]. 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.