The study compares the impact due to rice stem borers in two sites (Yaoundé and Ntui). It also shows the diversity of the African Rice Gall Midge (AfRGM) biotypes in southern Cameroon (Santchou, Ndop, Tonga, Ebolowa, Baïgom, Yaoundé and Ntui). The New Rice for Africa (NERICA) varieties 3, 8, 9 and 13 sown in Ntui were less attacked than those sown in Yaoundé. At both sites, damages ranged from 0.78% to 2.7%. In terms of diversity, the main stem-borer species were O. oryzivora, Diopsis apicalis, D. longiconis and Chilo zacconius. Molecular analyses of Orseolia oryzivora larvae collected in the localities of Santchou, Ndop, Tonga, Ebolowa, Baïgom and Yaoundé showed the existence of more than one O. oryzivora biotype in southern Cameroon's rice basins.