Natural enemies of maize stemborers on the highveld of Zimbabwe

The species composition of maize stemborers and prevalence of their natural enemies at five highveld (> 1200 m) sites were studied by random sampling of borer life stages in maize fields. Busseola fusca Fuller (Lepidoptera: N octuidae) was the dominant species and constituted 99 % of all larvae and p upae sampled during the study. Cotesia sesamiae Cameron (Hymenoptera: Braco nidae) was the most abundant and widely distributed parasitoid reared from B. fusca larvae, followed by Sturmiopsis parasitica (Curran) (Diptera: Tach inidae). Two hyperparasitoids, Aphanogmus fijiensis (Ferriere) (Hymenoptera : Ceraphronidae) (from C. sesamiae cocoons) and Dendrocerus rodhaini (Bequa ert) (Hymenoptera: Megaspilidae) (from S. parasitica puparia) were recorded . Preliminary data on the occurrence of C. sesamiae and S. parasitica sugge sted that these two parasitoids complement each other by partially partitio ning their niche and thus minimizing competition. However, firm conclusions concerning the host range and ecological adaptations of the two parasitoid s cannot be drawn until detailed studies have been conducted countrywide, e specially at lower altitudes (< 900 m a.s.l.) where Chilo partellus (Swinho e) (Lepidoptera: Pyralidae) and Sesamia calamistis Hampson (Lepidoptera: No ctuidae) predominate.