The systematics of the Culex pipiens complex.

It was concluded in 1951 that the Culex pipiens complex could best be treated as a single polytypic species. Since then observations on morphologically and biologically intermediate forms have strengthened this conclusion. These observations are supported by the results of experimental work on temperature tolerances, winter diapause and mating behaviour and by crossing experiments. Discussions of the possible role of cytoplasmic isolating factors in initiating speciation within the complex have not been sufficiently conclusive. The relative fitness of hybrids may be more important in determining their rarity or otherwise in particular populations than the rather tenuous mating barriers so far demonstrated. Since 1951 two further forms-C. p. australicus and C. globocoxitus-have been added to the complex, and there is evidence of extensive replacement of C. p. pipiens by C. torrentium in England. It is therefore unwise to neglect the dynamic aspects or the geography of the complex. A comprehensive review of the morphological aspects of the complex is badly needed.