Environmental persistence of Bacillus thuringiensis spores following aerial application

Soil and leaf populations of Bacillus thuringiensis (Bt) were monitored following aerial application of commercial Bt formulations at the rate of 72 billion international units per acre per year during a 5-year period. Data from soil sample spore counts suggested that Bt spores persisted in Wasatch forest soils for up to 2 years but they did not proliferate. Bt isolates were recovered from leaf samples 12 months post application from sprayed, previously sprayed and from nonsprayed areas. The frequency and diversity of Bt isolates recovered from leaves was independent of sample area spray history. In accordance with U.S. Forest Service criteria, aerial application of Bt during a 5-year period resulted in the eradication of gypsy moth (Lymantria dispar, L) from the Wasatch Front region of the Wasatch Mountain Range, Utah.