Study of a Naturally Occurring Population Intermediate between Culex P. Pipiens and C. P. Quinquefasciatus

Abstract
Summary and Conclusions The major part of this study is based on a naturally-occurring, anautogenous population of Culex p. pipiens in Lawrence, Kansas. This population is composed predominantly of the nominate subspecies, but many intermediates and a few C. p. quinquefasciatus (morphologically speaking) are present. Comparisons were made with anautogenous colonies from Alabama (C. p. quinquefasciatus) and Lawrence, Kansas (intermediates), an autogenous colony (“molestus”) from California, and with typical C. p. pipiens material from Minnesota. The autogenous colony is composed mostly of intermediates. It is believed that this is the first report of a naturally-occurring, autogenous strain of Culex p. pipiens which is not morphologically similar to the typical form. The characters used for study were the DV/D ratio of the males and the number of branches in the pentad hairs (1, 3, and 5) and siphonal tufts, the siphonal index, and the number of pecten spines on the siphon of the larvae. The two colonies established with material from the Lawrence population have shown an increase in the DV/D ratio since colonization. This shift from a form more like C. p. pipiens to one intermediate between C. p. pipiens and C. p. quinquefasciatus is probably produced in the laboratory by selection favoring C. p. quinquefasciatus. One breeding place was studied in detail to determine the seasonal morphological variation of the local population. The mean DV/D ratio in the male terminalia of samples from this breeding place increased throughout the breeding season. From individual egg rafts it could be seen that this increase in the mean ratio was largely due to the adding in of higher values later in the season which were not present earlier in the season. This probably indicates an influx of individuals which are more like C. p. quinquefasciatus from other areas, presumably from the south. Analyses of the variation in the branching of the siphonal tufts of larvae showed the same trend seen in the male terminalia. There appears to be a rather high correlation between the DV/D ratio of the male terminalia and the amount of branching in the basal siphonal tufts of larvae of this species in the Lawrence area. The results of this study are in agreement with the view that Culex p. pipiens and C. p. quinquefasciatus are biological entities which intergrade in the field and thus satisfy the classic requirements of subspecific status.
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