Larval growth of the two main maize stemborers, Busseola fusca (Fuller) (Lepidoptera, Noctuidae) and Eldana saccharina Walker (Lepidoptera, Pyralidae), in Côte d'Ivoire was studied as a function of temperature sums. Tunnelling by unit weight was similar for both species. Early attacks by B. fusca (infestation until 17 days after maize emergence) resulted in deadhearts or in growth reduction. A relation combining the date of infestation, the level of attack and the development stage of maize explains the observed damage. Later attacks by both borers result in differences in damage, which are related to the larval distribution in the stem, the compensation between maize yield components, and also to the presence of a more or less active larva in the cavity.