Flight Muscle Polymorphism in British Corixidae: Ecological Observations

Abstract

In Berkshire corixid species [Sigara falleni, S. dorsalis, S. scotti, Hespero-corixa castanea, S. lateralis, S. nigrolineata], usually have a main generation and a smaller partial second generation annually, the latter developing from eggs laid by the first adults of the main generation in June and July. The bugs of both generations overwinter and lay eggs in the following spring, some for the 2nd time. Studies on species polymorphic for flight in the development of the flight musculature have shown that a flightless form develops in early summer and again late in the year with the normal (flying) form developing during mid-summer and early autumn. The change in the development from the early flightless form to the normal form in early summer is related to rising temperature but the onset of development of the flightless bugs in late summer could not be satisfactorily related to temperature change. Experiments with 4 species demonstrated that larvae and newly molted imagines may be switched from the development of the flightless form to the normal form by moderate or high temperatures. Larvae are most sensitive to this factor early in the summer and when younger; older larvae or larvae taken late in the summer are less readily modified. The flightless form survived longer than the normal form and matured eggs earlier and at a faster rate in the laboratory. Similar differences were not, however, discovered in field populations. It was concluded (1) that the reduction of the alary structures confers advantage to the species through the greater efficiency of flightless bugs in the aquatic habitat and that (2) although there is a tendency for all species to be largely flightless this is only fully expressed in populations in permanent habitats.