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Abstract
Beauveria bassiana is being used as a biopesticide for many insect pests. Neem oil (azadirachtin) is an eco-safe popular botanical pesticide. A biopesticde with a neem compatible isolate of B. bassiana will enable their simultaneous use in pest management. A sample of 30 isolates of B. bassiana from culture collections was screened for compatibility with a commercial formulation of neem oil (Margoside®) at the field recommended dose (0.3%, v/v). Compatibility was tested in vitro through germination and growth assays. In all isolates, conidial germination was delayed but not significantly decreased by neem. In the growth assays, 23 isolates were found compatible with neem. In the neem sensitive isolates, growth was decreased but not totally inhibited. The effect of combined treatment with B. bassiana and neem in comparison to single treatments with either of them on Spodoptera litura Fabricius was tested in laboratory bioassays. The combined treatment was found to have synergistic effect on insect mortality when a B. bassiana isolate compatible with neem was used, while, with an isolate sensitive to neem, an antagonistic effect was observed.
Acknowledgements
We thank Dr R. A. Humber, USDA, ARS, Ithaca, NY, USA, Dr Kerry O‘Donnell, Microbial Properties Research, Peoria, IL, USA and Dr P. N. Chowdhury, Indian Type Culture collection, IARI, New Delhi, India for providing cultures of the fungal isolates. Uma K. Devi is thankful to CSIR Grant No 38(938)/97EMR-II, New Delhi and AP-NL BTU (BTU/P-76) for financial support. Murali C. Mohan is thankful to UGC, New Delhi, India for a Research fellowship. Narasimha P. Reddy is thankful to AP-NL BTU, Hyderabad for a research fellowship.