FACTORS AND CONSEQUENCES OF A NONFUNCTIONAL ALARY POLYMORPHISM IN PYRRHOCORIS-APTERUS (HETEROPTERA, PYRRHOCORIDAE)

Functional alary polymorphisms have been studied rather extensively in several insect species. This review article deals with factors contro lling wing polymorphism in a flightless species, Pyrrhocoris apterus ( L.), and discusses its adaptive significance and mechanisms for their persistence under natural conditions. The macropterous morph is determ ined by a recessive allele whose penetrance depends on photoperiod and temperature. Natural populations of this species contain a small frac tion of flightless macropters. The disadvantages of being a macropter (increase of development time, decrease of fecundity) are minimal, whi le the benefit may consist in the tendency to prereproductive arrest o f ovarian development in teneral females. It prevents establishing a s econd generation which would mostly die during the next winter. The me chanism of alary morph regulation may be an ancestral trait linking P, apterus with other polymorphic Heteroptera, while its decreased penet rance may be a derivative character. Variation in fitness due to alary morphs is small compared to the one associated with differences in bo dy size. The latter is environmentally determined, and not linked to t he genetic basis of wing polymorphism. In the ''mosaic'' of phenotypes of various size the significance of the genetic macroptery may be clo se to neutral.