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 cy clical seasonal selection acting on the morphs: predominantly black individ uals gain a reproductive advantage in the spring and summer, red forms gain ing an advantage during the winter. The veracity of this proposition is bas ed largely on a series of samples taken in Berlin-Buch in the 1930s by Timo feeff-Ressovsky (1940). These show considerable and reasonably consistent c yclical changes in the frequency of the morphs. We here give morph frequenc y 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 p ostulated by Timofeeff-Ressovsky. We discuss the possible explanations of t hese contradictory data sets and consider the mechanisms which might accoun t for the maintenance of melanic polymorphism in A. bipunctata in the absen ce of cyclical thermal melanism.