Rice Stalk Borer, Chilo plejedellus (Zink)

On the meso- and metathorax of the larva (right above the “prolegs”), the Mexican rice borer has only one seta (hair), while the rice stalk borer has two setae.

Ref: KEY TO SELECTED PYRALOIDEA (LEPIDOPTERA) LARVAE INTERCEPTED AT U. S. PORTS OF ENTRY: REVISION OF PYRALOIDEA IN “KEYS TO SOME FREQUENTLY INTERCEPTED LEPIDOPTEROUS LARVAE” BY WEISMAN, 1986, M. ALMA SOLIS.

Also, in general, the Mexican rice borer has light-colored hairs and head capsule while the rice stalk borer has dark hairs and head capsule.