Population dynamics of the woolly whitefly Aleurothrixus floccosus (Maskell) on sweet orange varieties in Nigeria and association of A. floccosus with the entomopathogenic fungi Aschersonia spp.

Introduction. Various whitefly species attack sweet oranges in Nigeria. The economic importance of these whiteflies varies from one area to another depending on prevailing environmental conditions. Trials were established to assess the relative susceptibility of sweet orange varieties to woolly whitefly Aleurothrixus floccosus (Maskell) attack, its population dynamics and the impact of its entomopathogenic fungi Aschersonia spp. in population management. Materials and methods. Four sweet orange varieties were used for the trials: Agege, Bende, Pineapple and Valencia. The population dynamics of A. floccosus and its fungi-colonised nymphs were monitored in 2006 and 2007 by sampling 24 leaves per tree at 14-day intervals. Average monthly precipitation, relative humidity and temperature were collated for the period of our study. Results and discussion. No significant difference was observed among the populations of A. floccosus nymphs or the level of nymphal infection by Aschersonia spp. in the sweet orange varieties. Higher numbers of woolly whitefly eggs and adults were observed on the Agege and Bende varieties in 2006 and 2007, but the results were only significantly different in 2007. In both years, the populations of eggs, nymphs and adults of A. floccosus and its entomopathogenic fungi Aschersonia spp. were relatively high in the dry season months of January to March, dropped during the rainy seasons and rose again from October. Evaluation of Aschersonia spp. impact showed active colonisation of whiteflies. Generally, our results showed that weather factors such as rainfall and relative humidity negatively influenced the woolly whitefly population. Conclusion. The association between the woolly whitefly population and fungi was beneficial and suggests that Aschersonia spp. could be considered as a potential biological control agent for A. floccosus.