Studies on the Pathogenicity of Native Entomopathogenic Fungal Isolates on the Cotton/Melon Aphid,Aphis gossypii(Homoptera: Aphididae) Glover under Different Temperature Regimes

Abstract

In an attempt to screen potential native entomopathogenic fungi for microbial control of cotton/melon aphid, we investigated the effect of temperature on the pathogenicity of some hyphomycete fungi. The virulence of four Beauveria and two Metarhizium isolates on adult Aphis gossypii was evaluated with a direct spraying bioassay at 20 °C, 25 °C and 30 °C temperature regimes under laboratory conditions. The result of the bioassay showed that at 25 °C and 30 °C, all the isolates were virulent. Accordingly, cumulative target percentage mortality of Aphis gossypii at 25 °C varied from 73.33–93.33 % mortality and LT50 ranged from 3.83 to 4.98 days while percentage cumulative target mortality and LT50 values at 30 °C ranged from 82.22–100 % and 3.23–4.02 days, respectively. A statistically significant interaction between fungal isolates and temperature indicated that the pathogenic nature of an isolate was dependent on the temperature conditions of the bioassay. The results of the present study suggest that the use of native entomopathogenic fungi as an alternative method to chemical pesticides may hold promise for the management of Aphis gossypii in Ethiopia.