PATHOGENICITY OF BEAUVERIA-BASSIANA, METARHIZIUM-ANISOPLIAE AND SERRATIA-MARCESCENS TO THE BANANA WEEVIL COSMOPOLITES-SORDIDUS

Two exotic fungal isolates, one of Beauveria bassiana (268-86) and ano ther of Metarhizium anisopliae (100-82), three local isolates of B. ba ssiana (isolates I, II, III) and one of the entomogenous bacteria, Ser ratia marcescens, were tested for pathogenicity against the banana wee vil Cosmopolites sordidus. All four isolates of B. bassiana and the on e of M. anisopliae were found to be pathogenic to third-instar larvae of C. sordidus, causing mortalities of 98-100% by 9 days post-exposure to dry fungal spores. M. anisopliae was the least pathogenic to larva e with LT50 of 4.2 days, compared to 3.5, 3.3, 3.6 and 4.0 respectivel y for isolates I, II, III and 268-86. B. bassiana was also pathogenic to adult C. sordidus, causing mortalities varying from 63-97% by 35 da ys post-exposure depending on isolate. As for larvae, M. anisopliae ex hibited low pathogenicity for the adult C. sordidus. In general, all t he fungi tested were less pathogenic to adult weevils (LT50 = 17.5; 12 .5; 8.0 and 22.0 days) for isolates I, II, III and 268-86 respectively , while isolate 100-82 failed to kill 50% of adults even by 35 days po st-exposure. Incubation of dead weevils in a moist environment led to development of surface mycelia starting from intersegmental junctions. Histopathology revealed extensive destruction of internal organs by h yphae which invaded most of the organs. The LT50 for S. marcescens aga inst C. sordidus larvae was 2.8 days. However, the bacterium did not k ill adult C. sordidus even at 10 times the concentration applied on la rvae.