Monterey Bt Liquid - Conc - Gallon - LG 6344OMRI Listed Monterey Bt Liquid Concentrateis a biological insecticide whose active ingredient is the beneficial bacteria Bacillus thuringiensis subspecies kurstaki strain SA 12 (Btk). This biopesticide works by introducing bacterial spores and toxins into the body of the insect larvae as it feeds on foliage. These toxins quickly disrupt, and soon completely stop, normal digestive functions of the pest insect. The infected larvae will cease eating