Humidity responses and water balance of riparian species of Bembidiini (Col., Carabidae)

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Abstract
1. The humidity responses of Asaphidion pallipes (Duftschmid) and Bembidion spp. were studied at various temperatures in choice chambers.2. Several species initially showed a hygropositive or indifferent response. Other species had a hygronegative reaction which later changed to a hygropositive one. The duration of the hygronegative reaction varied with species, age, temperature and relative humidity. B.litorale (Olivier) and B.semipunctatum (Donovan) change response when they have lost 8–9% of their initial body weight as water.3. The survival time of species of Bembidion under dry conditions was short compared with that reported for many other carabid beetles. Newly emerged adults of B.argenteolum Ahrens that had been kept away from sand for 3 weeks had lower transpiration rates than any other species. Young adult Bembidion had lower transpiration rates than those in the breeding phase, larvae and dead adults. Transpiration rate appeared to be inversely proportional to the relative humidity whereas there was a non‐linear increase in weight loss with increasing temperature.4. The species gain most water by drinking and/or from food.5. There was no correlation between humidity response and transpiration rate or ability to tolerate dry conditions of the species. There was, however, a correlation between behaviour/habitat affinity and humidity response. Diurnal species, living in sandy or silty, half shady‐exposed habitats had an initial hygronegative response, whereas those which hide among gravel/stones, leaves or vegetation were indifferent or hygropositive.