Virulence of Verticillium lecanii isolates in aphids determined by detached-leaf bioassay

Abstract

The virulence of three Verticillium lecanii isolates, designated as VL4, VL6, and VL10, was studied by treating three aphid species, Myzus persicae, Aphis gossypii, and Aphis citricola, with the entomopathogen. Treated aphids were transferred to detached leaves of Citrus aurantifolia on 1% water agar for pathogen incubation. The LC 50 on M. persicae of drench vs. spray treatment of VL10 after 6 days was 1.48 and 1.65 × 10 6 conidia/ml, respectively. V. lecanii was applied by spray in all remaining experiments. Population mortality began 3 days post-treatment and concentrations of 10 6–10 7 conidia/ml resulted in rapid mortality, reaching 100% after 4 days. Lower concentrations were also effective, but required more time to reach high mortality. VL4 required a concentration of 10 7 conidia/ml and 8 days to reach 100% mortality. The virulence of VL10 and VL6 was high in M. persicae and A. gossypii, whereas VL4 virulence was low in the three aphid species. Disease induced by VL10 and VL6 resulted in high mortality when only 33% of the populations of M. persicae and A. gossypii were treated by the fungus isolate. Aphis citricola populations were found to be least affected by the isolates regardless of the percentage of the population treated. These results indicated host specificity existed in the isolates of V. lecanii tested.