The Role of Natural Enemies in the Colour Polymorphism of Philaenus spumarius (L.)

In recent years a number of authors have suggested that the balanced polymorphism in Philaenus spumarius (L.) described by Halkka (1962), involving some twelve morphs, may be regulated by predators. Owen & Wiegert (1962) were the first to put forward this explanation but Hutchinson (1964) and Halkka et al. (1970) have subscribed to it as a possible hypothesis. By contrast, Farish & Scudder (1967) do not seem to think it is likely to be important whilst Adenuga (1968) dismisses selection by predators, but gives no evidence to support this. A more rigorous development of the thesis has recently been published by Thompson (1973) who deals with the theory of the problem but does not present verification. So far, positive evidence of attack of P. spumarius by visual hunters is fragmentary, except for the demonstration by Whittaker (1969, 1971) that in England it is attacked by a pipunculid fly Verrallia aucta Fallen. The purpose of this paper is to present the available evidence of predation and parasitism of Philaenus spumarius in England and to discuss its relevance to the balanced polymorphism.