Does thermal melanism maintain melanic polymorphism in the two-spot ladybird, Adalia bipunctata (Coleoptera: Coccinellidae)?

Melanic polymorphism in Adalia bipunctata is usually said to result from cyclical seasonal selection acting on the morphs: predominantly black individuals gain a reproductive advantage in the spring and summer, red forms gaining an advantage during the winter. The veracity of this proposition is based largely on a series of samples taken in Berlin-Buch in the 1930s by Timofeeff-Ressovsky (1940). These show considerable and reasonably consistent cyclical changes in the frequency of the morphs. We here give morph frequency data from sites in Russia and Britain, as well as citing data from Berlin-Buch (Schummer, 1983) which show no indication of the seasonal selection postulated by Timofeeff-Ressovsky. We discuss the possible explanations of these contradictory data sets and consider the mechanisms which might account for the maintenance of melanic polymorphism in A. bipunctata in the absence of cyclical thermal melanism.