[Objectives]  Holotrichia palallela Motschulsky (Coleoptera: Melolonthidae) is an important underground insect pest that seriously damages wheat, peanut, soybean, corn, chinese sorghum, and potato, crops. This paper lays the foundation for the biological control of H. palallela larvae with the Bt strains HD8E and HD8G, and may provide some excellent candidate genes for the development of insect-resistant, genetically modified, crops. [Methods]  Pathogenic changes in the midgut of grubs after ingestion of HD8E and HD8G were observed using transmission electron microscopy and an anatomical lens, respectively. [Results]  Pathogenic changes in the midgut of H. palallela larvae included the shedding of microvilli, degradation of longitudinal and circular muscles fibers, expansion of the intercellular space, swelling and breakage of the endoplasmic reticulum and mitochondrial cyclization. [Conclusion]  The two Bt strains HD8E and HD8G caused obvious pathogenic changes in the midguts of H. palallela larvae and visibly inhibited their feeding behavior.