The water-relations of Belba geniculosa Oudms. and other species of oribatid mites
1964 - Volume: 6 Issue: 1 pages: 199-228
A study has been made of the water-relations of free-living soil mites (Oribatidae) and especially of a common litter species, Belba geniculosa Oudms. 2. There is no significant difference in evaporation in either still or moving dry air. 3· When exposed to a range of different temperatures (10°C-70°C) in either dry air or in a constant saturation deficit of 9.2 mm Hg, the waterproofing cover of the adults has a marked critical temperature of about 45°C; in juveniles the corresponding temperature is about 40°C. 4· The normal behaviour of covering their soft unsclerotized integument with their cast skins and debris is not associated with the water-relations of the juveniles. This habit may be associated with (a) protection from predators and (b) protection of the waxy epicutile from abrasion. 5· The rate of evaporation of dead mites in dry air is greater than that of living mites. 6. Evaporation in dry air was increased when the integument was abraded. These mites also showed a greater increase in weight in saturated air than did untreated controls. 7· The rate of water-loss of abraded mites depends on (a) the shape but not necessarily the size of the abrasives (soft powders were least effective and hard ’gritty’ dusts most efficient) and (b) the frequency of the treatment. 8. A soft powder acted equally well as either an abrasive or as an adsorptive agent. 9· Living abraded mites slowly recovered their impermeability in saturated air, but this process was not entirely successful. 1o. Cold or hot chloroform treatment resulted in a marked increase in evaporation; the longer the treatment the greater the water-loss. The outer cover is thus a wax. II. Carbon dioxide has no effect on evaporation with living mites in dry or saturated air, nor is water-loss increased when they are pre-treated with the gas and then killed. B. geniculosa has no spiracular closing mechanism. 12. B. geniculosa has a well-developed respira tory system consisting of three pairs of tracheae. Comments are given on the observations of other workers. 13. Water-loss probably occurs mainly through the oral, anal and genital apertures. Losses by excretion are negligable. 14. Comments are given on the adaptation of certain species of oribatid mites to different environments on the basis of (a) the critical temperature of their waterproofing cover and (b) their type of respiratory system.
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