Insecticide resistance genes in Culex pipiens (Diptera: Culicidae) from Italy: esterase B locus at the DNA level.

Restriction fragment length polymorphism (RFLP) analysis at the esterase B locus was performed in samples from four populations of Italian Culex pipiens pipiens L. to identify correctly, at the molecular level, the resistance gene. The absence of the amplified B2 haplotype was confirmed, indicating that it has not increased in frequency after its detection in continental Italy around 1985. The B4 haplotype was detected in all populations at the same frequencies as a previous starch gel survey. The possibility that B4 amplification has occurred only once and has migrated across western Mediterranean region is supported by the data. A1 also was detected indirectly by the presence of its closely linked B allele. The B5 haplotype apparently was absent. No amplification at the esterase B locus was detected, except B4, indicating a low rate of occurrence of new amplification at this locus.