Abstract
Macropterous individuals of wing polymorphic semiaquatic bugs (Heteroptera: Gerromorpha) usually occur at a high fre- quency if there is a need to leave an unfavorable habitat or in a generation migrating to/from an overwintering site. Velia caprai (Veliidae) is usually found in unpredictable habitats, but the macropterous morph is rare. Laboratory, mesocosm and field experi- ments were used to test the hypothesis that individuals of this species migrate by walking rather than by flight. Laboratory experi- ments that focused on the development of macropterous morph under conditions that usually stimulate the development of this morph in water striders were unsuccessful. A high temperature shortened the duration of nymphal development, but no winged specimens of Velia caprai developed in the laboratory when reared under either high or low temperatures, long or short photoperiods or on the surface of water or wet filter paper. Mesocosm experiments with apterous adults revealed they are able to walk on land. Both the males and females dispersed by walking in semi-natural conditions. Long-term field experiments using mark and recapture confirmed that this species can disperse by walking. Apterous individuals can compensate for downstream drift by upstream terres- trial migration and colonize newly established pools and ditches even several tens of meters from source sites. The development of a macropterous morph in response to environmental factors is replaced by terrestrial dispersal in V. caprai.
Highlights
Most semi-aquatic bugs (Heteroptera: Gerromorpha) exhibit wing polymorphism, as many species have macropterous, brachypterous or apterous morphs (Andersen, 1982)
Recent laboratory experiments carried out concurrently with this study indicate that V. caprai does not produce significantly more winged individuals when crowded during nymphal development
This study recorded a positive effect of increased temperature on the rate of nymphal development of a non-gerrid species, V. caprai
Summary
Most semi-aquatic bugs (Heteroptera: Gerromorpha) exhibit wing polymorphism, as many species have macropterous, brachypterous or apterous morphs (Andersen, 1982). Both genetic and environmental factors determine the wing morph in semi-aquatic bugs (see Spence & Andersen, 1994). The forest streams occupied by V. caprai are unpredictable habitats as both beds of streams and water level vary during a season This species occupies ephemeral sites (Ditrich et al, 2008). The unpredictable nature of the habitat leads to the assumption that V. caprai is macropterous, or at least wing polymorphic This species is pterodimorphic with both macropterous and apterous morphs, but the macropterous morph is rare (Brinkhurst, 1959; Mielewczyk, 1980; Brönmark et al, 1985; Murray & Giller, 1991; Papáþek & Jandová, 2003). It does not examine how far, how often or what part of a population of V. caprai disperses terrestrially, but only if it disperses in this way
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