Production of spores of Metarhizium anisopliae and Beauveria bassiana on rice supplement with palm kernel cake and its pathogenicity against the larvae of Oryctes rhinoceros

The production of spores of isolates of entomopathogenic fungi Metarhizium anisopliae (MaTGK2, MaSE, MaST, MaBP) and Beauveria bassiana (BbF1, BbF5 and BbF10) on rice supplement with 2% (w/w) palm kernel cake (PKC) was estimated based on spore dry weight and spore number. The spore dry weight per bag of all isolates of Metarhizium grown on rice with PKC was ranging from 2.32g to 2.46g, significantly higher (P<0.05) than rice without PKC, which was between 0.85g and 1.16g. For all isolates of fungus Beauveria, the yield of spores grown on rice with and without PKC was not significantly different (P>0.05). The yield of spores was between 0.76g and 4.20g per bag. Based on the number of spores, two isolates of Metarhizium MaSE and MaTGK produced spores between 4.15 x 10⁷ spores/mI and 4.66 x 10⁷ spores/ml, significantly higher (P>0.05) than number of spores produced on rice without PKC. For all isolates of Beauveria, the numbers of spores produced on rice with and without PKC were no different. The isolate BbF10 produced the highest spores of 63.37 x 10⁷ spares/ml, followed by BbF5 (51.98 x 10⁷ spores/ml) and BbF1 (4.90 x 10⁷ spores/ml). Pathogenicity tests found all isolates of Metarhizium were highly pathogenic against the Oryctes larvae as compared with isolates Beauveria. Spores of Metarhizium produced on rice with and without PKC were equally pathogenic against the Oryctes larvae, caused between 92% and 100% mortality at 14 days after treatment (DAT). The mortality of Oryctes larvae treated with isolates Beauveria was low, ranging from 16% to 32% at 10 DAT. Percentage of dead larvae due to infection by isolates Metarhizium was ranging from 52% to 88%, significantly higher than isolates Beauveria, which was between 0% and 12%.