Potential of entomopathogenic fungi as biopesticides of cassava Bemisia tabaci whitefly

Abstract

Cassava-colonizing whitefly Bemisia tabaci transmit viruses causing cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). These are the greatest causes of cassava production loss in Africa. Current systems of managing B. tabaci are only partially effective. CMD and CBSD management is based heavily on preventative, phytosanitary measures, with inadequate remedial treatments available to control outbreaks when they occur. Plant breeding for resistance to CMD has been successful but it is vulnerable to the evolution of resistance-breaking viral strains. There has been limited progress in developing varieties resistant to cassava brown streak viruses. Because the spread and severity of viruses are associated with abundant whitefly populations, management needs to include a control strategy for the whiteflies. The use of synthetic toxicant pesticides is increasingly restricted due to health and environmental concerns. Consequently, emphasis is being placed on control using other methods. The adoption trend is accelerating for the use of entomopathogens as a component of IPM strategies, and companies are marketing these to an increasingly wide range of agricultural crops. Despite increasing adoption, entomopathogens are yet to be tested for efficacy against cassava B. tabaci in Africa. Bemisia tabaci is susceptible to infection by a range of genera of entomopathogenic fungi. Several commercial products are available against B. tabaci, but these have not been investigated in detail on cassava-colonizing whiteflies. Entomopathogenic biopesticides effective against cassava-colonising B. tabaci will enable farmers to control this pest hence drastically reducing the impact of its transmitted viruses on cassava yield. These fungi are recognized as having minimal risk to people and the environment and are straightforward to use as opposed to synthetic insecticides.