1. E. Plettner and K. N. Slessor, Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
2. M. L. Winston, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
3. J. E. Oliver, U.S. Department of Agriculture, Agricultural Research Service, Beltsville Agriculture Research Center, Beltsville, MD 20705-2350, USA.