EFFECTS OF TEMPERATURE AND FOOD LEVEL ON GROWTH AND DEVELOPMENT OF A PLANKTONIC WATER MITE

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mit e, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia a nd Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymph s and adult female mites increased with temperature; the duration of t he imagochrysalis stage decreased. Females grown at 10 degrees C were smaller at final size than females grown at 15 degrees C, 18 degrees C or 22 degrees C. Females reared at food levels of 15 or 30 prey 1(-1) grew more slowly and were smaller than those provided with 60 or 120 prey 1(-1). Nymphs grew more slowly when Daphnia were the only prey, t han when smaller prey were available. Food level did not affect nymph growth at 10 degrees C or 15 degrees C, but growth at 18 degrees C or 22 degrees C may have been slowed at the lowest food levels. Synergist ic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.