Field trials with the entomopathogenic fungus Beauveria bassiana against grasshoppers in Mali, West Africa, July 1990.
Spores of Beauveria bassiana in dormant oil were applied for the control of grasshoppers in open field sites and field cages in Mali. The fungus was applied at a concn of 1.2 × 1013 conidia/ha in open field sites and 2.3 × 109 and 4.9 × 109 conidia/ml in the field cages. The main acridid species present were Kraussella amabile, Cataloipus cymbiferus and Hieroglyphus daganensis, with more than 95% being 1st- to 3rd-instar nymphs. Grasshoppers were successfully infected in field plots, although post-treatment hatching and rainfall tended to obscure detection of infection and impact on population density. Incubation of dead hoppers confirmed the presence of B. bassiana 4-14 days after treatment. Two weeks after field treatment, the total mortality in cages of grasshoppers from treated and untreated plots was 72 and 22%, resp. Cage trials included sprayed and unsprayed hoppers, collected and treated at the site. Over the 19 days following treatment, the mortality of treated grasshoppers was approximately double that of untreated grasshoppers. Spores sprayed directly onto vegetation before grasshoppers were added to the cages did not result in significant mortality on most sampling dates. Direct contact spray treatment resulted in significant mortality in samples of grasshoppers caged after spraying. However, no direct reductions in populations were recorded.