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 o f the

entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin in the

management of C. sordidus.

The duration and spatial distribution o f 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

o f 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