Melanism in adalia ladybirds and declining air pollution in Birmingham

Abstract

The frequency of the melanic forms of Adalia bipunctata continued to fall at five sites in the Birmingham conurbation after the earlier decline in the 1960s monitored by E. R. Creed. The decline had levelled off by about 1978. The rate of change in melanic frequency was similar at each site with a more or less constant disadvantage to meianics of about ten percent from 1960 to 1978. The pattern of change shows a close correspondence to the levels of smoke pollution in Birmingham (r = +0·91) but a weaker association with sulphur dioxide (r = +0·72). It is argued that this follows from an influence on thermal melanism via the effect of smoke in reducing sunshine. The related A. decempunctata shows no changes in melanic frequencies at the same sites. This is consistent with previously inferred evidence for a lack of any influence of thermal melanism in this species. The responses of these ladybird beetles to changing air pollution are compared with that in the moth Biston betularia. © 1987, The Genetical Society of Great Britain.