Deciphering the biocontrol and immunomodulatory potential of Metarhabditis amsactae (Nematoda: Rhabditidae) against Corcyra cephalonica (Lepidoptera: Pyralidae)

In the present work, laboratory assays were performed to appraise the biocontrol potential of Metarhabditis amsactae, a Rhabditid nematode, against fifth instar larvae of Corcyra cephalonica. Virulence was tested at four different doses, i.e. 20, 40, 80 and 160 IJs/L (infective juveniles per larva) and mortality was documented from 24 up to 96 h of nematode treatment. Concentration and time-based enhancement in larval mortality was observed with 100% mortality recorded at 160 IJs/L after 96 h. Even at 20 IJs/L concentration, 60% and 76.7% larval mortality was recorded after 72 and 96 h, respectively. At 80 IJs/L, the mortality increased from 33.3% at 48 h to more than 90% at 96 h of nematode inoculation. Whereas, at 40 IJs/L, it enhanced from 16.7% at 48 h to 83.3% at 96 h. The effect of M. amsactae infection on the immune system of C. cephalonica was also evaluated at a dose of 100 IJs/L after 12, 24, 36 and 48 h time intervals. Insect larvae displayed augmented levels of antioxidant and detoxifying enzymes. The peak activities of superoxide dismutase, catalase, ascorbate peroxidase, phenol oxidase and glutathione-S-transferase in infected larvae were observed after 36 h, whereas acetylcholine esterase levels peaked after 48 h, as compared to control. Malondialdehyde content was also increased post nematode infection. Thus the current study is the first report that depicts the significant bioefficacy and immunomodulatory effects of M. amsactae against C. cephalonica under laboratory conditions. However, further research to assess its efficiency under field conditions is required.