Three insect species attacking oak forests in Missouri (walkingstick,Diapheromera femorata[Say]: orangestriped oakworm,Anisota senatoria[J. E. Smith]; and variable oakleaf caterpillar,Heterocampa manteo[Doubleday]) were susceptible to a commercial formulation ofBacillus thuringiensisvar.alesli. The median lethal concentration (LC50) values (international units × 103/milliliter per gram of insect) for each species were 6150, 2.2, and 8.6, respectively.