Why Big Species of Ladybird Beetles are Not Melanic

Melanic forms occur commonly in small species of coccinellid like Adalia bipunctata (L.) but are rare or absent in large species like Coccinella septempunctata L. Under direct irradiation coccinellids that are melanic show a greater temperature excess than non-melanic individuals. This was demonstrated for naturally occurring morphs of A. bipunctata and the normal non-melanic and artificial melanic forms of C. septempunctata. Temperature excess was shown to be a function of the elytral surface area that is coloured black. It is suggested that large species of coccinellid are not melanic because if they were their body temperatures would frequently reach deleterious levels on sunny days. Key-words: Thermal melanism, size, coccinellids