Suppression of the stem-borer Sesamia calamistis (Lepidoptera; Noctuidae) in maize following seed dressing, topical application and stem injection with African isolates of Beauveria bassiana

In a series of four experiments, African isolates of the hyphomycete fungus Beauveria bassiana were tested for their ability to provide protection against larvae of the stem-borer Sesamia calamistis in maize. Fungus was applied by dressing seeds with dry conidia, by topical application of conidial suspensions into leaf axils, and by injecting conidia into plant stems. Larvae were introduced to treated plants between 3 and 4 weeks after treatment, and the effect of treatment was assessed 1 or 2 weeks later. The frequency of dead plants was significantly reduced in experiments one and two, and there were non-significant reductions in recovery of live larvae. Stem-borer tunnel length was significantly reduced in experiment three, and a non-significant reduction in mean larval weight was observed. In the fourth experiment mean tunnel lengths and larval weights were reduced but the effects were non-significant. Few dead larvae were recovered and none exhibited symptoms of fungal infection. Fungal metabolites may mediate the observed effects and we conclude that the capacity of these isolates to reduce stem-borer damage in maize over an extended period is an encouraging step towards developing alternative pesticides for stem-borer control.