Abstract:Dendroctonus ponderosaeHopkins andIps pini(Say) are often found cohabitating inPinusspp. hosts, especially whenD. ponderosaeis in the endemic population phase. Although the adult stages are morphologically distinct, distinguishing between the species is difficult when only the larval stages are present. Using field collected specimens, several taxonomic characters of the larvae were identified which may be used to differentiate the two species. These results have application in studies of endemicD. ponderosaepopulations and competitive interactions betweenI. piniandD. ponderosaepopulations.