Screenhouse Transmission of Beauveria bassiana from Infected to Non-Infected Adults of Banana Weevil

Laboratory studies have revealed great potential of entomopathogenic fungus Beauveria bassiana for use against the banana weevil, Cosmopolites sordidus, in banana. Adult banana weevils exposed to wet conidia of Beauveria bassiana suffered high mortalities ranging from 50-70% by 40 days post exposure when a concentration of 1x10(9) was used in the laboratory with three isolates ICIPE 273, M313 and M207 which were selected on the basis of high virulence against C. sordidus and high sporulation. However, impractical field delivery methods and high costs associated with the application of B. bassiana against C. sordidus prevent its use and commercialisation in banana fields. The potential of utilizing infected weevils to disseminate the entomopathogen, Beauveria bassiana for control of the banana weevil was examined. In a small screenhouse experiment, the potential for the spread of the fungus within the weevil population was evaluated. It involved first introducing 18 non-infected banana weevils in potted banana plants and after an interval of two weeks introducing 2 banana weevils that were infected with the three isolates to check the rate of transmission. In the screenhouse their was no transmission from infected to non infected weevils since the infected weevils were dying at the top of the buckets while the non-infected had burrowed deep into the soil. The introduced weevils infected with fungus and that later died all showed signs of mycosis. For growth parameters, there was no significant difference in the height, girth and number of leaves between the treatments with the controls which had no weevils. We conclude that infected weevils cannot significantly transmit Beauveria bassiana to non-infected weevils.