From the Division of Parasitic Diseases, Centers for Disease Control and Prevention, Mailstop F22, 4770 Buford Highway, Chamblee, GA 30341, and Department of Biology, Emory University, Atlanta, GA 30322. M.Q.B. and O.M. were supported by grants from the John D. and Catherine T. MacArthur Grant to F.H.C. and the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases to N.J.B. We appreciate the exceptional efforts of C. F. Curtis of the London School of Hygiene and Tropical Medicine for supplying A. gambiae strains containing the and p alleles. We thank Brian Holloway and the staff of the CDC Biotechnology Core Facility for providing all oligonucleotide primers used in this study. H. Chang performed work contained herein in partial fulfillment of the requirements for his bachelor's degree senior research project at Emory University. Address correspondence to Dr. Benedict at the CDC.