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

ABSTRACT.

• 1 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.
• 2 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.
• 3 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.
• 4 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.
• 5 Thermal considerations do therefore play some role in the broad and complex selection regime of P.spumarius.