The impact of larval defoliation by Aproaerema modicella (Deventer) on the growth, development and yield of two groundnut cultivars (Kadiri 3 and NC Ac 17090) was studied under a naturally occurring, high density infestation. Defoliation by leaf-mining larvae did not increase plant mortality in either cultivar. In both cultivars, leaf and stem production were significantly lower in untreated plots than in the treated plots. Unsprayed plants of both cultivars produced fewer flowers, pegs, and pods per plant compared to plants of the same cultivar protected with monocrotophos. Fruit growth rates, however, were marginally higher in control plots than in treated plots. Pod yields were 35 and 44% lower, and haulm yields 25 and 20% lower, in Kadiri 3 and NC Ac 17090, respectively in untreated control plots compared to plots treated with insecticide. A linear relationship between leafminer density and pod and haulm yields was observed, and differences between cultivars were not significant.