Wing polymorphism commonly occurs in many insects, especially species of Orthoptera, Coleoptera, Homoptera, and Hemiptera (Harrison, 1980). The polymorphism consists of discrete differences in wing length with morphs exhibiting fully developed, reduced, or totally absent wings. In addition to differences in wing length, morphs often differ in a number of other characteristics such as degree of flight muscle development, duration of nymphal development, time to first reproduction, fertility and diapause (Anderson, 1973; Vepsäläinen, 1978; Harrison, 1980). Wing polymorphism is an attractive system for investigating the evolution of dispersal in natural populations (Vepsäläinen, 1978; Denno and Grissell, 1979; Harrison, 1980). A key step in such studies is the identification of the environmental and genetic components of morph determination. Numerous studies of insects from several different orders have clearly demonstrated that environmental variables such as photoperiod, temperature and density may strongly influence the development of an individual into a particular morph (see references in Harrison, 1980). However, the genetic component of morph determination is poorly understood. In this study we focused on the genetic influences of morph determination in the wingpolymorphic waterstrider, Limnoporus canaliculatus. We wished to determine if the inheritance of morph type could be explained by the single locus (or supergene) model proposed by most workers for other gerrid species, or whether a more complex genetic explanation was required. We used “split brood” experiments to determine if the mode of inheritance was different under different photoperiods as well as to assess the influence of photoperiod on morph determination
