Aims: Oryctes rhinoceros beetle is one of the most damaging pests of oil palm and cause high oil palm mortality. The empty fruit bunch mulch and rotten old trunk of oil palm in the field provide the organic matter for the breeding sites and increases the number of O. rhinoceros larvae. Bacillus thuringiensis as bioinsecticide can synthesize crystal proteins toxic to the larvae. The present study was aimed to find effective B. thuringiensis isolates as biopesticide against O. rhinoceros larvae. Methodology and results: Screening process was carried out through heating of soil sample suspension at 80 °C to eliminate the non-spore formers and plated onto T3 medium. Colony morphology was observed, followed by Gram and endospore staining. The crystal protein was observed by Coomassie Brilliant Blue (CBB) staining. Bioassay test was conducted by force-feed method followed by food contamination method. The results showed isolates SBB33 and SBB35 were able to infect and caused high mortality to the O. rhinoceros larvae. Isolates SBB33 and SBB35 showed the highest mortality against 1st instar larvae (94.44% and 75% respectively) and 3rd instar larvae (64.8% and 60% respectively) compared to control treatments. The 16S rRNA gene sequencing showed SBB33 has high similarity with B. thuringiensis strain 3S2-3, while SBB35 has high similarity with B. thuringiensis strain GCU_BTi10. Protein separation of the spore-crystal mixture by SDS-PAGE showed the prominence of 66 kDa protein band that was predicted to be Cry toxins which is specific to coleopterans insect. Conclusion, significance and impact of study Bacillus thuringiensis isolates SBB33 and SBB35 have high potential as biopesticides against O. rhinoceros larvae and could be used to control major pests in oil palm plantation.
Bacillus thuringiensis--isolation & ; purification ; Coleoptera