The expression of an insecticidal crystal protein gene of Bacillus thuringiensis under the control of the a-amylase gene promoter was investigated. The crylC gene, which encodes a protein known to have a unique activity against Spodoptera (armyworm) species, was used in this investigation. The cryIC gene was placed, along with the a-amylase promoter from B. subtilis, in a B. thuringiensis-derived cloning vector, generating a pair of recombinant plasmids, pSB744 and pSB745. The cloning vector that contains the minimal replicon of B. thuringiensis subsp. kurstaki HD73 is stably maintained in a variety of B. thuringiensis strains, as previously reported by Gamel and Piot (Gene 120:17-26, 1992). The present study confirmed that the recombinant plasmids are also stably maintained in B. thuringiensis subsp. kurstaki Cry-B and HD73 growing in media without selection pressure for at least 48 h. The cryIC gene on the recombinant plasmids were notably