The Potential of Beauveria Bassiana for the Management of Cosmopolites Sordidus (Germar, 1824) On Plantain {Musa, Aab)

Abstract

The banana weevil, Cosmopolites sordidus (Germar) in association with other pests and diseases, represents a threat to the production of plantain (Musa spp., AAB), the preferred staple food in Ghana. Biological control of the banana weevil was considered the most promising management option for small-scale plantain production and studies were, therefore, undertaken to determine the efficacy of the entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin in the management of C. sordidus. The duration and spatial distribution of the different developmental stages of C. sordidus within plantain plants were determined to provide background information for evaluation of B. bassiana against the banana weevil. The mean egg incubation period and the mean developmental period from larva to pupa and pupa to adult were 6.3 + 0.2, 28 } 0.6 and 7.1 } 0.3 days respectively. The developmental period from egg to adult ranged from 33 to 51 days with a mean of 40.4 } 0.7 days. Within the plantain plant, approximately 80% of the eggs were located in the rhizome, >80% of the larvae were found at the rhizome level and all of the pupated larvae were located in the rhizome, suggesting that this is where a biocontrol agent should be targeted, rather than the pseudostem. Three strains of B. bassiana were obtained and evaluated on the basis of virulence tests and potential for mass production. From the results of these tests, strain 1MI330194 o f B. bassiana was selected for subsequent studies. Laboratory studies using a water-based inoculum applied to corm pieces or pseudostem traps, showed that B. bassiana could control all stages of C. sordidus, with up to 21.3%, 36.4% and 42.3% of eggs, larvae and adults respectively showing signs of fungal disease. Pot experiments to compare different formulations of the strain IMI330194 against adult weevils showed that the highest mortality (>60%) was obtained with groundnut oil plus kerosene-based formulation of conidial powder (GOK-CP), groundnut oil-based formulation of conidial powder (GO-CP) and oil palm kernel cake-based formulation of conidia (OPKC-C). A persistence trial showed that OPKC-C o f IMI330194 still gave 61.0% weevil mortality one month after application, compared with only 12.3% for conidial powder (CP) of IMI330194 and 3.9% for the control with no conidia. In field trials with artificial weevil release, mortality of adult weevils exposed to CP and OPKC-C of IMI330194 ranged from 53.4 to 75.5%, compared to <8% in the control with no conidia. Under natural weevil infestation, 16.7% of plantain suckers treated with CP of IMI330194 and 19.4% of untreated suckers were killed by weevil attack. In contrast, none of the suckers planted with OPKC-C of IMI330194 were killed. A study on the spread of fungal conidia using artificially infected and non-infected adult weevils showed a possible dissemination of B. bassiana conidia from infected weevils up to 18m from the release point. On the basis of results from the present study, the strain IMI330194 of B. bassiana could clearly play a key role in the management of C. sordidus adults on plantain.