ELECTROPHORETIC VARIATION OF CULEX-PIPIENS FROM EGYPT AND ISRAEL

The genetic variation of Culex pipiens from Egypt and Israel was investigated on the basis of electrophoretic analysis of 17 enzyme loci: α-Gpdh, Mdh-1, Mdh-2, Me-1, Me-2, Idh-1, Idh-2, 6Pgdh, G3pdh, Got-1, Got-2, Hk-1, Adk, Pgm, Ald, Tpi and Gpi. Esterases were also studied for the occurrence of high-active patterns involved in organophosphate resistance. Allele frequencies have been compared with those available for C. pipiens from Italy and S France. The populations from Egypt and Israel are relatively homogeneous genetically: average Nei's D = 0.013 among Egyptian samples, 0.011 among Israeli ones, and 0.028 between the two groups. A poor correlation was observed in a number of cases between genetic differentiation of populations and their geographic distance, possibly due to unintentional transport by man. No evidence was found for the occurrence in Egypt and Israel of two genetically differentiated forms equivalent to pipiens and molestus in Europe. Egyptian and Israeli populations resemble European molestus more than European pipiens, as indicated by: (1) the allele frequencies at the loci Me-2, Got-1 and Gpi; (2) the rather low levels of genetic variability (H e = 0.12, P = 0.47, A = 1.54), similar to that found in a number of molestus populations from Europe; and (3) the values of genetic distance (average Nei's D of Egyptian and Israeli populations = 0.023 from Italian molestus and 0.056 from Italian pipiens). Egyptian and Israeli populations show high frequencies of individuals with highly active esterases (with the exception of two samples from the Red Sea coast), suggesting widespread organophosphate resistance in the study area. All the resistant individuals from Egypt and most of those from Israel show an esterase pattern with two very active bands (possibly controlled by the Est-2 and Est-3 loci), with electrophoretic characteristics identical to those recorded in organophosphate-resistant C. quinquefasciatus. As it is improbable that this high-active esterase pattern could have originated by introgression with resistant quinquefasciatus, it is suggested that different high-active esterase mutants were selected in different parts of C. pipiens range. The esterase pattern with a single, high-active band, typical of the European, resistant C. pipiens, was observed sporadically in samples from Israel, whereas a new three-band high-active esterase pattern, combining the others, was detected in samples from this country. The latter pattern presumably originates by hybridization of individuals carrying respectively the single-band and the two-band high-active pattern. The occurrence in Israel of individuals with the single-band high-active esterase pattern seems to have originated by passive transport of resistant specimens from Europe.