Natural enemies of the african armyworm,Spodoptera exempta(Walker) (Lepidoptera: Noctuidae), in Tanzania

Abstract

In Tanzania, residual populations ofSpodoptera exempta(Walker) may persist in highlands and river valleys, giving rise to the first outbreaks in the rainy season. To examine whether parasitoids could be a key factor in maintaining these populations at low density, samples were taken during outbreaks in eastern and north-eastern Tanzania from 1980 to 1984. Parasitism was high (around 50%) in the low density samples (below 25 larvae/m²) and low (below 17%) in the highest density ones (about 250–1200 larvae/m²). The number of outbreaks reported from the same administrative district as the sample site, and concurrent with it, was inversely related to parasitism level. The directly density dependent relationship between percentage parasitism and host density at lower densities, and the inversely density dependent one at higher densities, is similar to that found in parasitoid complexes of other Lepidoptera. Parasitoids in the rare braconid genusMeteorideawere recorded attackingS. exempta; this is the first published record from mainland Africa.