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SUMMARYNon-random mating may be involved in the maintenance of colour polymorphism in Adalia bipunctata. Mating choice experiments have been carried out on a stock of A. bipunctata from Keele. Specific frequencies of the melanic quadrimaculata form and the non-melanic typica form were placed in population cages or mating chambers and allowed to mate. The frequencies of the forms amongst mating pairs were scored. The results gave a good fit to a model of mixed sexual selection and assortative mating showing a strongly frequency dependent, non-assorting preference for quadrimaculata males in the matings.Data from the wild Keele population showed a similar preference for quadrimaculata males, and an excess of males of a second melanic phenotype, sexpustulata. Observation of courting pairs indicated that female choice determined frequency of mating. Field data from Keele also gave evidence of assortative mating between typica and another non-melanic form, annulata.

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