Pathogenicity of isolates of beauveria bassiana to the banana weevil

Abstract

Bananas constitute a major staple food crop for millions of people in developing countries, providing  energy  as well as important vitamins and minerals.  Its production in Kenya has been on the decline due to, among other factors, pests and disease of which  the banana weevil,  Cosmopolites  sordidus,  is the most important. The aim of this study was to screen ten isolates of the entomopathogenic fungus Beauveria bassiana for pathogencity against C.sordidus. Twenty weevils were inoculated with the fungus by  dipping them into a fungal suspension containing 1x108 conidia ml-1 for 11 seconds. The suspension was then drained out and pieces of banana corm introduced as food for the weevils. All the ten isolates of B. bassiana  tested were found to be pathogenic to  adult banana weevil causing mortalities of between 20-50% by 40 days post exposure. ICIPE 273 was the most pathogenic isolate killing 50% of adults, followed by M313 at 36% and M207 at 30%. Isolates KE300, M221, ICIPE 50, M573, M618, M470 and ICIPE 279 killed less than 30% of the weevils, ICIPE 279 was the least pathogenic isolate to the adult C. sordidus killing 6% of the inoculated weevils. The dead weevils were incubated in sterile moist filter papers in Petri dishes for two weeks and fungal mycelia was observed on the surface of the weevils starting from intersegmental junctions. Mortality caused by fungus was confirmed by microscopic examination. Since isolate ICIPE 273 has reasonable pathogenicity to  C.sordidus  and field/screenhouse studies are recommended to validate the findings.