Fungus,Verticillium lecanii as one of insect pathogens has a broad range of hosts. In this research, pathogenicity of hyphomycete, V. lecanii (DAOM 198499 isolate), was investigated with six different concentrations against third nymphal stage of the aphid, Myzus persicae under laboratory conditions (23 ± 1°?, 95 ± 5% RH and 16L: 8D). Three days after inoculation, aphid mortality was initiated. Minimum and maximum mortality, achieved with fungul suspension of 104 and 108 conidia per ml were 51.1 and 100 percent (after 10 days) respectively. Analysis of lethal effect of various concentrations of V. lecanii against M. persicae, indicated that there were significant difference in aphid mortality. LC50 and LT50 values were estimated by probit analysis and life test on aphid mortality during 12 days after treatment. LC50 value was 1.4 × 104 conidia/ml-1. LT50 values for concentrations of 104, 105, 106, 107 and 108 conidia/ml-1 were 10, 10, 9, 8 and 6 days, respectively. The results showed that net reproduction rate of aphids (R0) decreased significantly when the concentration increased. Based on these results as well as results of other researchs, it is implied that V. lecanii (DAOM 198499 isolate) has the potential to be used as a biocontrol agent against aphids in greenhouse conditions
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