Stem borers are one of the most important insect pests that could infest rice plants from seedling to maturity and thus play a major role in crop losses. The study of its mandible that is used in feeding of stem borer would help understand the mechanisms and variations that could affect the adaptation and modification affecting severity of infestation. In this study, the mandible of two population of stem borers, the yellow stem borer (Scirpophaga incertulas and the striped stem borer (Chilo suppressalis) in three rice varieties IR-66, Pioneer 77 and Bigante were used to analyze the adaptation with regards to mandible shape in relation to rice variety in the same geographical location using outline-based (elliptic Fourier) geometric morphometric (GM) analysis to determine the shape variations in the left and right mandible of two population of stem borers. Further, scatter plot method was used to illustrate variations in the shapes of the mandibles between populations. Results of this study showed symmetrical shape variations in the right and left mandible of the two species of stem borers and their accumulation to the kind of rice plant varieties were not selective.