Bacillus thuringiensis subspecies kurstaki and aizawai are important control agents for lepidopteran pests. Bioassays were designed to test B. t. kurstaki and aizawai against second- and-fourth instar black cutworm larvae with and without Bacillus sp. NFD2 and Pseudomonas sp. FNFD1 bacteria. B. thuringiensis subsp. aizawai (XenTari) was more toxic to both second- and fourth-instar black cutworm, Agrolis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), larvae than B. t. kurstaki (DiPel) at 7 d after treatment (DAT). When DiPel was combined with NFD2 or FNFD1 versus second instars, the LC₅₀s were 5.0× and 4.7× lower, respectively, than with DiPel alone. DiPel combined with both NFD2 and FNFD1 versus second instars resulted in an LC₅₀ value 7.7× lower than with DiPel alone. When XenTari was combined with NFD2 or FNFD1 versus second instars, the LC₅₀s were 5.2× and 3.8× lower, respectively, than with XenTari alone. XenTari combined with both NFD2 and FNFD1 versus second instars resulted in an LC₅₀ 9.7× lower than with XenTari alone. When DiPel was combined with NFD2 or FNFD1 versus fourth instars, the LC₅₀s were 4.4× and 3.4× lower, respectively, than with DiPel alone. DiPel combined with both NFD2 and FNFD1 versus fourth instars resulted in an LC₅₀ 5.0× lower than with DiPel alone. When XenTari was combined with NFD2 or FNFD1 versus fourth instars, the LC₅₀s were 5.7× and 3.3× lower, respectively, than with XenTari alone. XenTari combined with both NFD2 and FNFD1 versus fourth instars resulted in an LC₅₀ 6.7× lower than with XenTari alone.