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RNA interference (RNAi) has been developed and used as an emerging strategy for pest management. Here, an entomopathogen <i>Bacillus thuringiensis</i> (<i>Bt</i>) was used to express the dsRNA for the control of <i>Plutella xylostella</i>. A vector containing a 325-bp fragment of the conserved region of <i>P. xylostella</i> arginine kinase gene (<i>PxAK</i>) flanking in two ends with the promoter Pro3α was developed and transferred into <i>Bt</i> 8010 and BMB171, and consequently engineered <i>Bt</i> strains 8010AKi and BMB171AKi expressing dsRNA of <i>PxAK</i> were developed. The two engineered <i>Bt</i> strains were separately mixed with <i>Bt</i> 8010 in a series of ratios, and then fed to the <i>P. xylostella</i> larvae. We found that 8010:8010AKi of 9:1 and 8010:BMB171AKi of 7:3 caused a higher mortality than <i>Bt</i> 8010. <i>PxAK</i> expression levels in the individuals treated with the mixtures, 8010AKi and BMB171Aki, were lower than that in the control. The intrinsic rate of increase (<i>r</i>) and net reproductive rate (<i>R</i>₀) of the population treated with 8010:8010AKi of 9:1 were lower than those of the population treated with <i>Bt</i> 8010 or 8010AKi. We developed a <i>Bt</i>-mediated insect RNAi for the control of <i>P. xylostella</i> and demonstrated a practical approach to integrating the entomopathogen with RNAi technique for the pest management.