Abstract:
The success of entomopathogenic fungi as microbial control agents ultimately depends on the use of the right propagule, formulated in an optimum fashion and applied at the right time to a susceptible host. In this study, the pathogenicity of six isolates of Beauveria bassiana (Bals.) Vuill. and 14 isolates of Metarhizium anisopliae (Metsch.) Sorok to Metopolophium dirhodum (Walker) and Rhopalosiphum padi (Linneaus) was for the first time determined in the laboratory. The differential susceptibility of different developmental stages to fungal infection and the effect of different fungal formulations on aphid mortality and aphid population growth attributes was also established. Time-mortality (LT50) laboratory study results showed that three out of the twenty screened isolates, identifiable as ICIPE 84, ICIPE 51 and ICIPE 23 registered significantly (P< 0.05) shorter periods of lethal infection, indicating high level of pathogenicity or virulence of the select isolates. Further doseresponse bioassays indicated that ICIPE 51 outperformed isolates ICIPE 23 and ICIPE 84 by recording the lowest LC50 and LC90 values. Virulence for all nymphal stages was dosedependent and mortality increased with host aphids’ maturity and over time. Low doses of the isolate did not affect pre-lethal reproductive effects, such as fecundity and intrinsic rate of increase. Both aphid species were significantly (P< 0.05) more fecund in their early adulthood, suggesting the stage as ideal for biopesticide management intervention. Greenhouse and field trials established that M. anisopliae isolate ICIPE 51 has a great potential for management of R. padi and M. dirhodum, particularly when formulated in oil. However, if the entomopathogen is to be applied prophylactically, before infestation of wheat with aphids, then a sticker-based formulation would be most preferable. Additional work is required to further critically evaluate the bio-efficacy of the virulent strains in field conditions, examine methods for mass production and long term preservation as well as explore possibilities of integrating the use of the fungal isolates with other control tactics as a component of Integrated Pest Management (IPM) programmes.
