Isolation of entomopathogenic fungi from the soil and their pathogenicity to two fruit fly species (Diptera: Tephritidae)

The occurrence of deuteromycetous entomopathogenic fungi was determined by examining 224 soil samples from 19 locations in three climatic zones of Mauritius. Three sites were sampled per location: one site under vegetables cultivation, one site under sugar cane plantation and one natural site each within 1 km of each other. Soil samples were baited with the waxmoth larvae Galleria mellonella L. and incubated in the dark at 15, 20, 25 or 30 degrees C for 7, 14 and 21 days. Entomopathogenic fungi were isolated from 77 out of 224 (38.6%) soil samples. Metarhizium anisopliae was isolated from 42 (18.8%) samples, Beauveria bassiana from 24 (10.7%), Metarhizium spp. and Paecilomyces fumosoroseus from 5 (2.2%) each and Beauveria spp. from 1 (0.4%). It was observed that M. anisopliae was isolated more frequently from soils under vegetables as compared to soils under sugarcane or habitat with natural vegetation. Beauveria bassiana was isolated more frequently at the lowest incubation temperature (15 degrees C) while M. anisopliae isolates were recovered more frequently at higher temperatures (25 and 30 degrees C). The pathogenicity of seven isolates of M. anisopliae, five isolates of B. bassiana and two isolates of P. fumosoroseus towards the adults of Bactrocera zonata and Bactrocera cucurbitae was tested by topical application of conidial suspension of 1 x 10(6) conidia/ml. All the isolates tested were pathogenic to the two fruit fly species. Mortality of B. zonata varied between 12.0 and 98.0% and between 2.0 and 94.0% in B. cucurbitae at 5 days post-treatment. Our results suggest that entomopathogenic fungi present locally, could be integrated for the control of B. zonata and B. cucurbitae.