Astrong mandible of the leaf folder Cnaphalocrocismedinalislarva is used in scraping leaf tissues of rice during feeding.It is for this reason that in the control of this pest, host plant resistance traits were focused the physical and biochemical attributes of the leaf that discourages the insect from feeding. Breeding rice resistant to leaffolders have resulted to the identification of some varieties resistant to the insect pest. However, the deployment of varieties with specific genes for resistance were soon found to succumb to pest attacks. Resistance breakdown was attributed to the insect’s capability to overcome the resistance factors. It is believed that certain genotypes of the insect pest were able to feed on these resistant plants and this could be due to differences in the mandibles of the larvae. This study was therefore conducted to find out whether the mandible shape of the rice leaf folder C.medinaliswould likely differ with respect to their utilization of the different rice varieties. Geometric morphometric (GM) methods particularly elliptic Fourier analysis (EFA) was employed to describe the shapes of the mandibles of C.medinalisinfesting rice varieties with different genes for resistance. Resultsof the study showed significant differences in shapes of the mandibles among populations of C.medinalisfeeding on different rice varieties. Variations in the mandible shapes could possibly be due to selection and/or co-speciation of the insect pest with the host plant.