Effect of Entomofungal Pathogens on Mortality of Three Aphid Species

The pathogenicity of twelve fungal isolates belonging to Beauveria basiana (Bals.) Vuill., Metarhizium allisopliae (Metschinikoff) Sorokin and Verticillium lecanii (Zimmerman) against Aphis craccivora Koch, Aphis gossypii Glover and Rhopalosiphum maidis Fitch was studied using detached leaf bioassay technique. All twelve isolates of thc three fungi were found to be pathogenic to A. craccivora and A. gossypii at a concentration of 1x107 spores/ml. All isolates except Bb3 and Bb4 of B. bassiana were pathogenic to R. maidis. The mortality ranged from 2 to 74 per cent in A. craccivora, 14 to 80.8 percent in A. gossypii and 6 to 50 per cent in R. maidis. Bb5a isolate of B. bassiana caused highest per cent mortality in A. gossypii (80.8%.) and R. maidis (50%) indicating its broad spectrum action. VII isolate of V. lecanii recorded maximum mortality (80.8%) of A. craccivora. R. maidis was relatively less susceptible to the three fungi than A. craccivora and A. gossypii. The LC50 of Bb5a for three days old nymphs of A. gossypii was 6.57x105 spores/ml. The LT₅₀ of Bb5a for three days old nymphs of A. gossypii was highest (9.67 days) for the lowest dose of 106 spores/ml, which decreased with increasing concentration. The highest dose 109 spores/ml recorded the lowest LT₅₀ of 1.76 days.