Temperature and the colour polymorphism of Philaenus spumarius (Homoptera: Aphrophoridae)

The spittle bug, Philaenus spumarius (L.), has eleven distinct elytral colour pattern morphs in Britain, of which three are designated non‐melanic and eight melanic. Frequencies of different morphs vary between populations. The role of thermal factors in the maintenance of the balanced polymorphism was investigated by measurements of dorsal reflectance and body temperature when artifically irradiated. Non‐melanic forms had higher reflectances and showed lower temperature excesses when irradiated. There was considerable variation in reflectance for the populi–typicus morph group, and trilineatus is therefore the only true‘non‐melanic’morph. For samples along altitudinal transects in three Scottish glens, trilineatus frequencies were found to be negatively and populi‐typicus and melanic frequencies positively correlated with altitude. Thermal considerations do therefore play some role in the broad and complex selection regime of P.spumarius.