1. Department of Biology, University of Ottawa, Ottawa K1N 6N5, Canada
2. Current address: National Research Council, Canada, Steacie Institute for Molecular Science, Ottawa, Ontario K1A 0R6, Canada
3. Current address: Merck Sharpe and Dohme, Insecticide Development Laboratories, P.O. Box 2000, Rahway, NJ 07065
4. Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile