V. Pasteur, E. Perrot, F. Poulin, M. Rousset, and . Weill, The Entente Interdepartementale pour la Demoustication du Littoral Mediterraneen (EID) is particularly acknowledged for providing details on treatments and resistance data of 1973 samples. This work was financed in part by a Programme Environnement, Vie and Societe of the CNRS (GDR 1105), the region, ACC (SV39503037), and a CEE grant (ERBCHRXCT930172). TG benefited from a MESR fellowship

H. Aka-ike, Information theory and an extension of the maximum likelihood principle, International symposium on information theory. Akademiai Kiadi, pp.267-281, 1973.

. Anonymous, Rapport d' Acitivite, Entente Interdepartementale pour la Dernoustication du Littoral Mediterraneen, 1991.

D. E. Axelrod, K. Baggerly, and M. Kimmel, Gene amplification by unequal sister chromatid exchange: probabilistic modeling and analysis of drug resistance data, J. Theor. BioI, vol.168, pp.151-159, 1994.

R. J. Baker and . Nelder, The glim system. ReI. 3.77. Algorithm Groups, 1985.

B. C. Bonnlng and J. Hemingway, Identification of reduced fitness associated with an insecticide resistance gene in Culex pipiens by micro titre plate tests, Med. Vet. Entomol, vol.5, pp.377-379, 1991.

D. Bourguet, M. Raymond, D. Fournier, C. A. Malcolm, J. Toutant et al., Existence of two acetylcholinesterases in the mosquito Culex pipiens (Diptera: Culicidae), J. Neurochem, vol.67, pp.2115-2123, 1996.
URL : https://hal.archives-ouvertes.fr/hal-02687493

E. Caspari, Pleiotropic gene action, Evolution, vol.6, pp.1-18, 1952.

C. Chevillon, Evolution de mecanismes adaptatifs: flux geniques, selection et centre-selection, 1994.

C. Chevillon, N. Pasteur, M. Marquine, D. Heyse, and M. R. , Population structure and dynamics of selected genes in the mosquito Culex pipiens, Evolution, vol.49, pp.997-1007, 1995.
URL : https://hal.archives-ouvertes.fr/halsde-00201443

C. Chevillon, D. Bourguet, N. Rousset, and M. R. Pasteur, Pleiotropy of adaptive changes in populations: comparisons among insecticide resistance genes in Culex pipiens, Genet. Res, vol.68, pp.195-203, 1997.
URL : https://hal.archives-ouvertes.fr/halsde-00201473

G. M. Clarke, The genetic and molecular basis of developmental stability: the Lucillia story, Trends Ecol. Evol, vol.12, pp.89-91, 1997.

G. M. Clarke and J. Mckenzie, Developmental stability of insecticide resistant phenotypes in blowfly: a result of canalizing selection, Nature, vol.325, pp.345-346, 1987.

E. M. Cohan, E. C. King, and P. Zawadzki, Amelioration of the deleterious pleiotropic effects of an adaptive mutation in Bacillus subtilis, Evolution, vol.48, pp.81-95, 1994.

M. J. Crawley, GUM for ecologists, 1993.

J. F. Crow, Genetics of insect resistance to chemicals, Annu. Rev. Entomol, vol.2, pp.227-246, 1957.

A. G. Davies, A. Y. Game, Z. Chen, T. J. Williams, S. Goodall et al., Scalloped wings is the Lucilia cuprima Notch homologue and a candidate for the Modifier of fitness and asymmetry of diazinon resistance, Genetics, vol.143, pp.1321-1337, 1996.

E. De-stordeur, Esterases in the mosquito Culex pipiens pipiens L.: formal genetics and polymorphism of adult esterases, Biochem. Genet, vol.14, pp.481-493, 1976.

J. Felsenstein, The theoretical population genetics of variable selection and migration, Annu. Rev. Genet, vol.10, pp.253-280, 1976.

R. H. Ffrench-constant, N. M. Anthony, D. Andreev, and K. Aronstein, Single versus multiple origins of insecticide resistance: inferences from the cyclodiene resistance gene Rdl, ill T. M. Brown, pp.106-116, 1996.

R. A. Fisher, The possible modification of the responses of wild type to reccurrent mutations, Am. Nat, vol.62, pp.115-126, 1928.

T. Guillemaud, S. Rooker, N. Pasteur, and M. R. , Testing the unique amplification event and the worldwide migration hypothesis of insecticide resistance genes with sequence data, Heredity, vol.77, pp.535-543, 1996.
URL : https://hal.archives-ouvertes.fr/halsde-00201468

S. W. Guo and A. E. Thompson, Performing the exact test of Hardy-Weinberg proportions for multiple alleles, Biometrics, vol.48, pp.361-372, 1992.

M. J. Guttieri, C. V. Eberlein, C. A. Mallory-smith, and D. C. Thill, Molecular genetics of target-site resistance to acetolactate synthase inhibiting herbicides, pp.10-16, 1996.

J. B. Haldane, The causes of evolution, 1932.

H. Kless, M. Oren-shamir, S. Malkin, L. Mcintosh, and M. E. , The D-E region of the Dl protein is involved in multiple quinone and herbicide interactions in photosystem II, Biochemistry, vol.33, pp.10501-10507, 1994.

K. Y. Lee, J. Townsend, J. Tepperman, M. Black, C. E. Chui et al., The molecular basis of sulfonylurea herbicide resistance in tobacco, EMBO J, vol.7, pp.1241-1248, 1988.

R. E. Lenski, Experimental studies of pleiotropy and epistasis in Escherichia coli. II. Compensation for maladaptive effects associated with resistance to virus T4, Evolution, vol.42, pp.433-440, 1988.

M. Magnin, The statistics of natural selection, Resistance aux insecticides organophosphores: detection, caracterisation, genetique et dynamique dans les populations naturelles. Ph.D. diss. Univ. of Paris VI, 1985.

J. A. Mckenzie, Measuring fitness and intergenic interactions: the evolution of resistance to diazinon in Lucilia cuprina, Genetica, vol.90, pp.227-237, 1993.

, Selection at the diazinon resistance locus in overwintering populations of Lucilia cuprina (the Australian sheep blowfly), Heredity, vol.73, pp.57-64, 1994.

J. A. Mckenzie and A. Y. Game, Diazinon resistance in Lucilia cuprina; mapping of a fitness modifier, Heredity, vol.59, pp.371-381, 1987.

J. A. Mckenzie and A. Purvis, Chromosomal localisation of fitness modifiers of diazinon resistance genotypes of Lucilia cuprina, Heredity, vol.53, pp.625-634, 1984.

J. A. Mckenzie, J. M. Dearn, and M. J. Whitten, Genetics basis of resistance to diazinon in victorian populations of the australian sheep blowfly, Lucilia cuprina, Austr. J. BioI. Sci, vol.33, pp.85-95, 1980.

J. A. Mckenzie, M. J. Whitten, and M. A. Adena, The effect of genetic background on the fitness of diazinon resistance genotypes of the australian sheep blowfly, Lucilia cuprina. Heredity, vol.49, pp.1-9, 1982.

C. Mouches, M. Magnin, J. Berge, M. De, V. Silvestri et al., Overproduction of detoxifying esterases in organophosphate-resistant Culex mosquitoes and their presence in other insects, Proc. Nat. Acad. Sci. USA, vol.84, pp.2113-2116, 1987.
URL : https://hal.archives-ouvertes.fr/hal-02716705

T. Nagylaki, Conditions for the existence of clines, Genetics, vol.80, pp.595-615, 1975.

C. Nielsen-leroux, J. Pasquier, G. Charles, B. Sinegre, N. Gaven et al., Resistance to Bacillus sphaericus involves different mechanisms in Culex pipiens (Diptera: Culicidae) larvae, J. Med. Entomol, vol.34, pp.321-327, 1997.
URL : https://hal.archives-ouvertes.fr/halsde-00201778

N. Pasteur, N. Pasteur, and G. Sinegre, Recherche de genetique chez Culex pipiens pipiens L. Polymorphisme enzymatique, autogenese et resistance aux insecticides organophosphores, Biochem. Genet, vol.13, pp.789-803, 1975.

N. Pasteur, G. Sinegre, and A. Gabinaud, Est-2 and Est-3 polymorphism in Culex pipiens L. from southern France in relation to organophosphate resistance, Biochem. Genet, vol.19, pp.499-508, 1981.

N. Pasteur, G. Pasteur, J. Catalan, F. Bonhomme, and A. J. Brit-ton-davidian, Practical isozyme genetics, 1988.

M. Poirie, M. Raymond, and N. Pasteur, Identification of two distinct amplifications of the esterase B locus in Culex pipiens (L.) mosquitoes from mediterranean countries, Biochem. Genet, vol.30, pp.13-26, 1992.

M. Raymond and M. Marquine, Evolution of insecticide resistance in Culex pipiens populations: the Corsican paradox, J. Evoi. BioI, vol.7, pp.315-337, 1994.

M. Raymond and F. R. , GENEPOP. Verso 1.2. A population genetics software for exact tests and ecumenicism, J Hered, vol.86, pp.248-249, 1995.
URL : https://hal.archives-ouvertes.fr/halsde-00186383

M. Raymond, B. Gaven, N. Pasteur, and G. Sinegre, , 1985.

, Etude de la resistance au chlorpyrifos 11 partir de quelques souches du moustique Culex pipiens L. du sud de la France, Genet. Sei. Evoi, vol.17, pp.73-88

M. Raymond, N. Pasteur, D. Fournier, A. Cuany, J. B. Berge et al., Le gene d'une acetylcholinesterase insensible au propoxur determine la resistance de Culex pipiens L. 11 cet insecticide, C. R. Acad. Sci. Paris, Serie III, vol.300, pp.509-512, 1985.
URL : https://hal.archives-ouvertes.fr/hal-02721472

M. Raymond, D. Fournier, J. Bride, A. Cuany, J. Berge et al., Identification of resistance mechanisms in Culex pipiens (Diptera: Culicidae) from southern France: insensitive acetylcholinesterase and detoxifying oxidases, J. Econom. Entomoi, vol.79, pp.1452-1458, 1986.
URL : https://hal.archives-ouvertes.fr/hal-02718761

M. Raymond, V. Beyssat-arnaouty, N. Sivasubramanian, C. Mouches, G. P. Georghiou et al., Amplification of various esterase Bs responsible for organophosphate resistance in Culex mosquitoes, Biochem. Genet, vol.27, pp.417-423, 1989.

M. Raymond, D. Heckel, and J. G. Scott, Interaction between pesticide genes: model and experiment, Genetics, vol.123, pp.543-551, 1989.

M. Raymond, A. Callaghan, P. Fort, and N. Pasteur, Worldwide migration of amplified insecticide resistance genes in mosquitoes, Nature, vol.350, pp.151-153, 1991.

M. Raymond, C. L. Qiao, and A. Callaghan, Esterase polymorphism in insecticide susceptible populations of the mosquito Culex pipiens, Genet. Res, vol.67, pp.19-26, 1996.

Y. Rivet, M. Marquine, and M. R. , French mosquito populations invaded by A2-B2 esterases causing insecticide resistance, BioI. J. Lin. Soc, vol.49, pp.249-255, 1993.

J. Rochaix and J. E. , Function and assembly of photosystem. II. Genetics and molecular analysis, Trends Biochern. Sci, vol.13, pp.56-59, 1988.

S. Rooker, T. Guillemaud, J. Berge, N. Pasteur, and A. M. Ray-mond, Coamplification of A and B esterase genes as a single unit in Culex pipiens mosquitoes, Heredity, vol.77, pp.555-561, 1996.
URL : https://hal.archives-ouvertes.fr/halsde-00201469

C. Severini, R. Romi, M. Marinucci, and M. R. , Mechanisms of insecticide resistance in the field populations of Culex pipiens from Italy, J. Am. Mosq. Contr. Assoc, vol.9, pp.164-168, 1993.

C. Severini, R. Romi, M. Marinucci, T. Guillemaud, and A. M. Raymond, press. Esterase A5-B5 in organophosphate-resistant Culex pipiens from Italy. Med. Vet. Entomoi

G. Sinegre, M. Babinot, J. Quermel, and B. G. , First field occurrence of Culex pipiens resistance to Bacillus sphaericus in southern France. P. 17 in VIIIth European meeting of society for vector ecology, 1994.

J. Szymura and N. H. Barton, Genetic analysis of a hybrid zone between the fire-bellied toads, Bombina bombina and B. variegata, near Cracow in southern Poland, Evolution, vol.40, pp.1141-1159, 1986.

M. Taylor and R. Feyereisen, Molecular biology and evolution of resistance to toxicants, Mol. BioI. Evoi, vol.13, pp.719-734, 1996.

A. Trebst, The molecular basis of plant resistance to photo system, II. Herbicides. Pp. 44-51 in T. M. Brown, 1996.

F. Villani and J. Hemingway, The detection and interaction of multiple organophosphorus and carbamate insecticide resistance genes in field populations of Culex pipiens from Italy, Pest. Biochem. Physioi, vol.27, pp.218-246, 1987.

M. S. Williamson, D. Martinez-torrez, C. A. Hick, N. Cas-tells, and A. L. Devonshire, Analysis of sodium-channel gene sequences in pyrethroid-resistant houseflies: progress toward a molecular diagnostic for knockdown resistant (kdr), 1996.

, Molecular genetics and evolution of pesticide resistance, in T. M. Brown, pp.52-61

M. Wirth, M. Marquine, G. P. Georghiou, and N. Pasteur, Esterase A2 and B2 in Culex quiquefasciatus (Diptera: Culicidae): role in organophosphate resistance and linkage, J. Econom. Entomoi, vol.27, pp.202-206, 1990.

S. Wright, Evolution and the genetics of populations, 1968.