Melanism in Adalia bipunctata L.(Col., Coccinellidae) and its relationship to atmospheric pollution.
Abstract
The evidence for the suggestion that smoke pollution is the main selective factor determining melanic frequencies of the polymorphic Adalia bipunctata (L.) in Britain [cf. RAE/A 63, 2989] is reviewed and discussed in relation to an alternative hypothesis that the species exhibits thermal melanism. A highly significant negative correlation is shown between annual hours of bright sunshine and melanic frequency. It is suggested that the melanic morphs will have a selective advantage over the non-melanics because of a greater ability to absorb solar radiation. This advantage may be important in cooler and less sunny conditions, including those where smoke reduces sunshine levels. Experimets showed that the melanic morphs have higher internal temperatures and greater activity than the typical morphs when illuminated at the same ambient temperature. It is concluded that A. bipunctata exhibits thermal melanism [cf. 63, 2988] and cannot be used as a biological indicator of smoke pollution.