MOLECULAR ANALYSIS OF CYCLODIENE RESISTANCE-ASSOCIATED MUTATIONS AMONG POPULATIONS OF THE SWEET-POTATO WHITEFLY BEMISIA-TABACI

Two polymerase chain reaction (PCR)-based molecular diagnostics were u sed to investigate whether cyclodiene resistance is uniquely associate d with the novel ''B'' biotype of the sweetpotato whitefly Bemisia tab aci (Gennadius) and thus establish whether resistance could have acted as a driving force in the recent and rapid spread of this biotype. Pr evious studies have shown that a single point mutation coding for an a lanine to serine replacement in the Drosophila Rdl gene confers high l evels of resistance to cyclodiene insecticides. Following identificati on of an analogous point mutation in the B. tabaci Rdl homologue, PCR amplification of specific alleles demonstrated that the corresponding alanine to serine replacement is not confined to the B biotype but is also present in indigenous whitefly populations found on crop plants. Single-stranded conformational polymorphism (SSCP) analysis of the sam e region of the Rdl gene was used to confirm whitefly genotype and exa mine the degree of nucleotide polymorphism among whitefly strains. A c omparison of SSCP banding patterns revealed a remarkable lack of nucle otide variation among strains conforming to the B biotype, whereas sev eral of the non-B strains exhibited different banding patterns. Sequen ce analysis of these strains revealed one or more nucleotide polymerph isms including a novel resistance-associated mutation in one collectio n from the Sudan. These results show that cyclodiene resistance is not uniquely associated with the B biotype. However, the lack of genetic variability in the Rdl gene among B strains is consistent with the rec ent origin and spread of this novel biotype. (C) 1995 Academic Press, Inc.