Peanuts transformed with the synthetic cry8Ea1 gene flanked by MARs are a potentially effective control strategy against white grubs. Cry8Ea1 protein levels of the construct containing MARs were increased by 2.5 times. White grubs are now recognized as the most important pests of peanut worldwide. A synthetic cry8Ea1 gene, which was toxic to Holotrichia parallela larvae, was expressed in chimeric peanut roots using an Agrobacterium rhizogenes-mediated transformation system. The relative mRNA and protein levels of the cry8Ea1 gene were confirmed by quantitative real-time PCR and ELISA, respectively. The effects of matrix attachment regions (MARs) on the expression and activity of the cry8Ea1 gene were analyzed. The average expression level of cry8Ea1 in peanut roots was higher for the plants harboring constructs flanked by MARs from tobacco. Moreover, differing from previous studies, the synthetic cry8Ea1 gene flanked by MARs showed more variation in protein levels than mRNA levels. These composite plants containing cry8Ea1 gene flanked by MARs exhibited a high toxicity against Holotrichia parallela larvae as shown by bioassay analysis, thus offering a potential effective combination to control subterranean insects in peanuts.