Abstract:

Indigenous Beauveria bassiana and Metarhiziun anisopliae isolates (41) from Uganda
entomopathogenic fungi from other geographical origins. Similarities were observed in
the isolates’ ability to produce protease, elastase, chitobiosidase and esterases but the
isozymes patterns and DNA fingerprinting by PCR, for banana weevil and the
Galleria soil baited isolates were quite distinct with some primers. All the indigenous
isolates were pathogenic to the banana weevil, Cosmopolites sordidus (Germar)
(Coleoptera Curculionidae) and many were more pathogenic to the banana weevil than
foreign isolates.
One indigenous B. bassiana isolate (code G41), was selected for testing under pot and
field conditions because it was highly pathogenic to C. sordidus and showed superior
growth and sporulation compared to other isolates. B. bassiana G41 was tested as
maize formulation, soil formulation, oil formulation and water formulation with the
maize and soil formulation showing higher efficacy. The three delivery systems
evaluated for B. bassiana were: (1) application to banana suckers, (2) application with
banana pseudostem and disc-on-stump traps and (3) application on top soil around the
banana plants.
Application of B. bassiana (G41) to banana suckers caused infection to all banana
weevil stages, significantly reduced the weevil damage as compared to untreated
suckers, but was unable to reduce damage below economically damaging levels under
were characterized by biochemical and molecular methods with reference to field conditions.
B. bassiana applied to banana pseudostem and disc-on-stump traps was more infective
under pot (20-50% weevils killed within 7 days) than field conditions (less than 15% in
14 days). The moist conditions under the traps, in addition to attracting weevils, also
provided a favourable environment for extra sporulation of the maize and soil B.
bassiana formulations and this enabled the fungus to remain potentially effective.
B. bassiana was persistent in the soil and caused 10-100% infection in banana weevil
exposed to formulations sampled from the field 1-5 months after treatment application.
B. bassiana applied on top soil around the banana plants caused up to 16% infection in
the field banana weevils, significantly reduced the banana weevil population and the
internal mean damage of the pre-flowered or the maiden suckers and the peepers
below the 5% economic threshold. These results suggest that B. bassiana application
on top soil was the best delivery system.
Exposure to sunlight and high temperature delayed conidia germination but B.
Observations were also made on the effects of ash-based soil amendments, moisture
content and micro-organisms that might influence the efficacy of B. bassiana under
field conditions.
bassiana expressed ability to recover from some of the adverse conditions