Efficacy of an Omani strain of Cordyceps javanica and its culture filtrate against whitefly (Bemisia tabaci) under laboratory conditions

摘要

In this study, an entomopathogenic fungus was isolated from whitefly (Bemisia tabaci ) cadaver samples collected from eggplant fields in Barka, Oman. The fungus was identified as Cordyceps javanica based on sequence analysis of ribosomal DNA internal transcribed spacer (ITS) regions. Under in vitro conditions, the fungus was able to grow between 20°C and 30°C, with a maximum growth at 30°C. No growth occurred at 35°C. Studies on the efficacy of different concentrations of conidia of C. javanica against whitefly nymphs revealed that the mortality rate increased with the increase in concentrations of inoculum. About 95.6 ± 2.1 corrected mortality was recorded at a concentration of 10~(7) conidia ml~(−1) after 7 days of treatment. The culture filtrate of C. javanica exhibited toxicity against whitefly nymphs and recorded 61.3 ± 9.5 corrected mortality after 48 h of treatment. There was no significant difference between the mortality caused by conidial suspension and culture filtrate. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of 17 compounds in the culture filtrate of C. javanica . Lauric acid was present in the largest amount (28.7) and the long chain (C22-25) hydrocarbons contributed 38.3. This is the first report on the isolation and characterization of C. javanica from B. tabaci from Oman.