Effect of Soil and Sand on Infectivity of Entomopathogenic Fungi against White Grub Holotrichia longipennis

Biopesticides are economically viable, socially acceptable, environmentally friendly, self-perpetuating, extremely persistent, and cost-effective, their application has grown in importance as a key strategy in integrated pest management (IPM). Bioassay studies were carried out in the whitegrub laboratory of Department of Entomology, CSK HPKV, Palampur (H.P.) to evaluate the potential of Beauveria bassiana and Metarhiziun anisopliae, and to study the effect of soil and sand on infectivity against first, second and third instar grubs of Holotrichia longipennis. The first instar larvae of H. longipennis were found to be most susceptible to both entomopathogenic fungi when treated in soil, with the mean mortality rate of 61.56 and 63.90 per cent for B. bassiana and M. anisopliae, respectively compared to second and third instar. A positive correlation between the inoculation concentration and the grub mortality was observed, irrespective of age, in all the instars. The mean mortality rates of H. longipennis were calculated to be 61.56, 50.67 and 43.56 per cent for first, second and third instar grubs, respectively when treated with B. bassiana with the concentration of 1x108 conidia/ ml in soil, but the mortality rates decreased to 57.18, 47.19 and 38.67 per cent for first, second and third instar grubs when sand was used as substrate. Similarly, when the grubs were treated with M. anisopliae in soil, the mortality rate was recorded as 63.90, 53.77 and 44.88 per cent for first, second and third instar grubs respectively, but when sand was used as substrate, the mortality reduced to 61.33, 50.22 and 43.55 per cent for first, second and third instar grubs, respectively. Soil outperformed sand due to better moisture retention and organic matter content in soil, which provides favourable environmental conditions for conidia to grow and infect the host. These findings hold great promise for the use of entomopathogenic fungi for Integrated pest management of white grubs.