The morphology of sternite VIII as well as that of the spermatheca of the females of Dendroctonus frontalis (Zimmermann) and D. mexicanus (Hopkins) is presented, and these structures are proposed, for the first time, as an alternative for the identification of these species. The main characteristic of sternite VIII is the shape and sclerotization of their central ridge, more sclerotized and with better defined borders in D. mexicanus. As for spermathecae, the most useful characteristic is their internal ornamentation which in D. frontalis covers the posterior half of the capsule and has twice as many traverse grooves as in D. mexicanus, where the grooves are more spaced and only cover the posterior third.