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

Prospects for the biological control of locusts and grasshoppers have become much brighter during the last ten years thanks to a number of international research projects. This paper examines a number of options, including one that is ready for immediate implementation: the mycoinsecticide, Green Muscle®, based on the fungus Metarhizium anisopliae (flavoviride) var. acridum. It has been registered in South Africa and other African countries are likely to follow during 1999. Trial results on grasshoppers and several locust species have been very encouraging, and preliminary tests on red locusts show potential as well. Recent research on pheromones also points to some interesting possibilities, both when used alone and in combination with a mycoinsecticide. Finally, microsporidian protozoans and rhabditid nematodes show some promise for long-term suppression of red locust populations, but more research and development is needed to demonstrate their potential.

The influence of three cultivars of Sorghum bicolor (L.) on the activity of the fungus Metarhizium anisopliae on the stemborer Chilo partellus was investigated in the field and laboratory. Fungal activity in the field varied with the plant cultivar and the inoculum concentration. Larvae fed on different cultivars and inoculated with the fungus in the laboratory did not vary in their susceptibility to the pathogen. However, time to 50% mortality (LT50) of the larvae was shorter in cultivar IS 1044 than in cultivars ICS 3 and ICS 4. Compatibility of the fungus with cultivars is therefore an important consideration when using fungi for the biological control of stemborers.

A technique for infecting adult tsetse with an entomopathogenic fungus was developed and tested in the laboratory. A nitrocellulose filter membrane (Millipore) was used as substrate for retaining conidia after fitration, and a cylindrical plastic tube served as a chamber for the flies. The technique was designed to allow accurate estimation of inoculum on the substrate, thereby permitting comparison of virulence during the screening of fungal pathogens against tsetse flies. Glossina morsitans centralis adults were susceptible to Metarhizium anisopliae at all doses tested, and mortalities were dose dependent. No significant differences in mortalities were observed when flies were exposed for different durations to the pathogen. The number of conidia picked up by flies varied considerably with exposure time and concentration.