Boring behavior of first and third instar larvae of the rice stem borer (RSB), Chilo suppressalis, on calcium silicate (Si)-treated susceptible (Shanyou63) and moderately resistant (Yanfeng47) rice cultivars was compared in terms of percentage of larvae bored (PLB), percentage of larvae penetrated (PLP) and penetration duration (PD), and number of silica cells in leaf sheaths and SiO2 content in soil and rice culms were determined, with the aims to clarify the influence of Si amendment on RSB boring behavior and whether there are differences in the Si-mediated influence regarding larval instars and rice cultivars. PLB decreased 5%-28% with increase in Si addition. PLP did not differ among Si treatments or between rice cultivars for the first instars; for the third instars, PLP significantly decreased 10%-40% with increase in Si supply and was 10% to 30% lower on Yanfeng47 than on Shanyou63. Si addition significantly prolonged PD in the first instars and, Yanfeng47 compared to Shanyou63 extended PD in the third instars. Increased SiO2 content in rice culms due to Si addition contributed to the reduction in PLP and prolong in PD of the third instar larvae. The current results indicate that Si amendment may contribute to the suppression of C. suppressalis directly through impeding larval penetration, and indirectly by delaying penetration, resulting in prolonged exposure of larvae to other control measures; Si supply impairs penetration more strongly in the third instars than in the first instars; and, susceptible rice cultivar benefits more from Si addition than resistant one in deterring boring by RSB larvae.