ABSTRACT.1. This paper tests the hypothesis that selection for dispersal ability within a species influences not only the occurrence and extent of wing reduction but also the tendency or ability of the macropterous individuals to fly.2. Flight thresholds of four species of waterstriders (Hemiptera; Gerridae) were assessed using a tethered flight technique. The species tested varied from monomorphic macropterous (Limnoporus dissortisDrake and Harris), through seasonally polymorphic (Gerris comatusDrake and Hottes andG. buenoiKirkaldy), to primarily apterous (G.remigisSay).3. Condition of the indirect, mesothoracic flight muscles, and presence or absence of mature or developing eggs (for females) were determined by dissection of all individuals immediately following flight testing. Only individuals with normal muscles were included in the analysis of flight thresholds.4. Comparisons among species revealed that average flight threshold and extent of flight muscle histolysis were negatively associated with the proportion of macropterous individuals. Wing reduction was also associated with significant seasonal variation in flight threshold, particularly among females.5. These results support our initial hypothesis, and further indicate that, within the Gerridae, dispersal tendency depends not only on the proportion of macropters but also on the dispersal capability of the macropterous individuals.