Pathogenicity of granule formulations of Metarhizium anispoliae against the larvae of the oil palm rhinoceros beetle , Oryctes rhinoceros (L.)

Granule formulations consisting of mycelia and spores of Metarhizium anisopliae var. major as the active ingredient were produced and tested against the larvae of Oryctes rhinoceros. The effect of the medium pH on the production of mycelia was investigated, and the granule compositions were optimized. The fungus produced higher yields of mycelial pellets (0.58 g) at pH=8 as compared to pH=5, 6 or 7. Granules prepared from mycelia with the growing medium (G+MM) improved fungal growth (100%) and sporulation (87.2%) as compared to granules prepared from the mycelia alone (G+M) (growth and sporulation, 62.4% and 47.6%, respectively). The amounts of ingredients, such as kaolin and rice bran used in making the granules, were then optimized. The weight of granules increased as the amount of kaolin and rice bran increased, but granule quality was reduced. The highest quality granules (with growth 98.5%, sporulation 88.6% and dry weight 1249 g) were prepared with 925 g kaolin and 400 g rice bran. The pathogenicity of the G+MM granules was tested against the third instar larvae of O. rhinoceros. The test showed that at 20 days after treatment (DAT), treatment with rates of 1.0 g and 2.0 g granules/box caused 90% mortality, which was as high as with the treatment using pure spore solutions (96%). The G+MM granules produced more spores and more quickly than granules made from spores (G+Sp). Both types of granules produced 0.42-6.60 x 106 spores/granule. Results of the bioassay indicated that application of G+MM and G+Sp at rates of 3 g, 6 g and 9 g killed 100% the third instar larvae as early as at 18 DAT. Infection level increased as the application rate increased. G+MM and G+Sp applied at 9 g/box caused the highest infection of 93.3% in the larvae. The potential use of the granule formulation to control O. rhinoceros in the field was also discussed