Assessment of Entomopathogenic Fungi for the Biocontrol of Sucking Insect Pests: Pertaining to Red Spider Mites (Tetranychus urticae)

Abstract

Aim: The study was undertaken to assess the efficiency and select the virulent entomopathogenic fungal isolates for the biological control of red spider mites (Tetranychus urticae) under in vitro conditions. Place and Duration of Work: The study was carried out in the Department of Agricultural Microbiology, University of Agricultural Sciences, GKVK, Bangalore, India. Methodology: A leaf disc bioassay was employed to assess the virulence of entomopathogenic fungal isolates isolated from 2 agro-climatic zones of Karnataka, India under In vitro conditions. The lethal concentration and lethal time were determined by obtaining the mortality data from various conidial concentrations and the data was analysed using Probit analysis. For molecular identification the fungal DNA was isolated through Cetyl trimethyl ammonium bromide (CTAB) extraction buffer, followed by purification through phenol/chloroform extraction and precipitation with isopropanol or ethanol, and the ITS regions of the 18S rDNA were amplificated using universal primers. Results: Out of 81 fungal isolates, 16 (19.25%) showed insecticidal activity under in vitro conditions. The results of the in vitro studies revealed that two isolates, ENPF-8 and ENPF-58 had significantly higher mortality rates (93-95 %) against mites at a concentration of 1x108 conidia/ml after 9 days after treatment (DAT). The virulent fungal isolates were identified as Isaria fumosorosea (with accession no: MT997932) and Hirsutella thompsonii (MT997936) using the sequencing of the ITS region of the 18S rDNA gene. H. thompsonii (ENPF-58) was found to be more virulent against mites, with lower LC50 (7.6×105 conidia/ml) and LT50 (5.7, 5.89, and 5.99 days) values compared to the other EPF. Conclusion: Based on results, it is evidenced that though all isolates caused mortality in the mite population but the percent mortality was varied. Based on these results, H. thompsonii (MT997935) and Isaria fumosorosea (MT997932) could be a promising biocontrol agent due to their high virulence against mites.