Possibilities for flight in the carabid beetle Nebria brevicollis (F.) : The importance of food during larval growth.

The carabid beetle Nebria brevicollis (F.), despite being macropterous, has a very low flight potential. Only a few percent of the beetles has functional flight muscles, flight motivation is low, and the period favourable for flight is short. The inability to fly is caused mainly by arrested development of the flight muscles. Dispersers are formed only under favourable conditions in the larval stages as shown by laboratory experiments (much food, short daylength). In N. brevicollis dispersal by flight cannot be considered as a reaction to deteriorating conditions but just the other way round. Because of the usually low numbers of potential dispersers conditions during larval development are apparently suboptimal. However, N. brevicollis is widespread and abundant in our area. The "choice" of using energy for the metabolic costs of larval growth, and only secondarily for the building up of flight muscles does not prevent the species from fully exploiting the habitat.