1. Department of Biochemistry and Microbiology, Rhodes University, P.O. Box 94, Makhanda 6140, South Africa
2. Centre for Biological Control, Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Makhanda 6140, South Africa
3. Citrus Research International, P.O. Box 5095, Walmer, Gqeberha 6065, South Africa