1. Plant Health Management Division, 1International Institute of Tropical Agriculture, 08 BP 0932, Cotonou, Benin;
2. CABI Biosciences, Silwood Park, Ascot, Berks. SL5 7TA, UK;
3. Lethbridge Research Centre, 3Agriculture and Agri-Food Canada, PO Box 3000 Main, Lethbridge, Alberta T1J 4BI, Canada;
4. Leverhulme Unit for Population Biology and Biological Control, Natural Environment Research Council Centre for Population Biology and CABI Biosciences, Silwood Park, Ascot, Berks. SL5 7TA, UK;