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The respiratory activity in adults of two species of aquatic Coleoptera, Hydrous piceus and Dytiscus marginalis, was examined to assess the physiological responses of the oxygen content variations of their air stores, called physical gills. The respiration rates were measured at two temperature ranges between 19° C and 30° C by means of a dissolved oxygen metre. The two species showed no significant differences in oxygen consumption, but water temperature affected oxygen gains in the bubbles. The effect of body weight on respiration level did not differ significantly within the two temperature ranges in either species because of the similar weights among individuals. The oxygen exchange between the physical gills and the surrounding water can be used as a measure of the respiratory metabolism of these insects and of their interactions with the surrounding environment.

The genetic differences in three populations of Sigara s. str. belonging to S. striata, S. dorsalis, and S. basalis, distributed in northern (Veneto, South Tyrol) and central (Umbria, Molise) Italy, were assayed by horizontal starch electrophoresis. Adult specimens were examined. Twelve enzymes were assayed, eight of which gave satisfactory results. Five of the eight alloenzymes were further investigated to differentiate the three species: phos‐phoglucomutase (Pgm‐1, Pgm‐2), esterase (Est‐1, Est‐2, Est‐3), su‐peroxide dismutase (Sod‐1, Sod‐2), phosphoglucose isomerase (Pgi‐1, Pgi‐2), isocitrate dehydrogenase (Idh) coding for 10 studied loci. A total of 208 adults of the three taxa (142 for S. basalis, 49 for 5. dorsalis, and 17 for 5. striata) were analysed. Nei's unbiased genetic distances were calculated and values between congeneric species ranged from 0.009 to 0.25, as illustrated in a phenogramme constructed by the unweighted pair‐group cluster analysis method. Sigara basalis presented the h...