SCREENING OF BEAUVERIA BASSIANA ISOLATES TO THE BANANA WEEVIL AND HORIZONTAL TRANSMISSION UNDER LABORATORY CONDITIONS

Abstract

The effective use of the entomopathogen Beauveria bassiana for the management of banana weevil needs evaluations of isolates under laboratory conditions for the most virulent strains. For screening work, 20 adult weevils were contaminated by dipping into a conidial suspension titrated 1x108 conidia ml‐1 for 11 seconds. The excess of suspension was drained and banana corm was introduced as food in 250ml plastic containers. All the screened isolates of B. bassiana tested were found to be pathogenic to the adult C. sordidus causing mortalities of between 20‐51% by 40 days post exposure. ICIPE 273 was the most pathogenic killing 51% of adults, followed by ICIPE 645 36% and ICIPE 281 30%. The rest ICIPE 603, ICIPE 289, ICIPE 50, ICIPE 284, ICIPE 283, ICIPE 647 and ICIPE 279 had a kill of less than 30% with ICIPE 279 being the least pathogenic to the adult C. sordidus. From the screening work done, the three best isolates ICIPE 273, ICIPE 645 and ICIPE 281 were tested at a concentration of 1 x 109 and they caused mortalities varying from 50‐70%, 40 days after exposure. In disease transmission experiment it was possible to transmit infection from two weevils dosed with conidia at 1 x 109 from the three strains of Beauveria bassiana to a group of 18 non infected banana weevils in 250ml plastic containers mainly through contact. The rate of transmission from infected to non infected weevils caused mortalities of between 24 – 26% of horizontal infection for the tested isolates. Incubation of dead weevils in clean petri dishes with moist sterile filter papers led to development of mycelia on the surface starting from intersegmental junctions, confirming that the mortality was caused by fungus. Dead weevils from the control had no fungal growth. Based on these results, ICIPE 273 shows promise for the control of banana weevil and should be subjected to further studies.