Biocontrol potential of native entomopathogenic nematodes against coconut rhinoceros beetle, Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae) under laboratory conditions

Abstract

Abstract Background India is the world's leading producer of coconuts. Many biotic and abiotic constrains limit global palm yield and among the biotic factors, the coconut rhinoceros beetle, Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae) is the major problem in India. The adult beetle attacks the unopened leaves and inflorescences, resulting in a yield loss of more than 10%. O. rhinoceros grubs and adults have different feeding habits as the adults feed on plant tissues, whereas the grubs primarily feed on rotting organic matter. Non-feeding stage, i.e. the larval stage, which is cryptic in nature and spends nearly 90–160 days in the breeding site, is amenable to any control measures so as to reduce the population of actual damaging adult stage. However, indiscriminate use of chemical insecticides has created a lot of environmental and regulatory issues, thus warranting an ecologically safe and environmental friendly alternative option. Hence, indigenous entomopathogenic nematode (EPN) strains, viz. Heterorhabditis indica (CPCRI-Hi1), Steinernema abbasi (CPCRI-Sa1), and S. carpocapsae (CPCRI-Sc1), virulence and reproductive capacity were evaluated against second instar larvae of O. rhinoceros. Results Oryctes rhinoceros larval susceptibility to EPN significantly varied with the treatment dose and period of exposure. The highest larval mortality was observed with S. carpocapsae (100%), and S. abbasi (92%) at 10 days post treatment, whereas H. indica strain induced 72% mortality. At 72 h of incubation, the LC50 values of Sc1, Sa1 and Hi1 strains were 1078, 1663 and 9780 IJs larva−1, respectively. With different concentration of EPN tested, the production of infective juveniles (IJs) inside the cadavers for Sc1, Sa1 and Hi1 varied between 3223–10,365; 4722–96,572 and 3483–85,453 larvae−1, respectively. Conclusion Based on the virulence, reproductive capacity, searching ability and LC50 values, it is suggested that strain Sc1 have great potential as a biocontrol agent for the Oryctes management in coconut palms under humid tropical ecosystem. Present study found the effective native strain against O. rhinoceros, and its field efficacy should be tested further to include the EPNs in the integrated pest management program in coconut.