A description is given of the behaviour of oribatid mites from West Africa and North America in temperature gradients. The results of the experiments may be summarized as follows:—
- (i)West African species had a tolerance zone of 18° C.-36° C. compared with 16° C.-28° C. in North American species.
- (ii)West African species had an upper critical temperature and an upper lethal temperature of 37° C. and 38° C.-40: C. respectively, compared with 30° C. and 30° C.-32° C. respectively in North American species.
- (iii)Most West African species had a preference for conditions in the 24° C.-31° C. range, compared with 21° C.-260 C, in North American species.
The differences between the two groups depended very largely on the temperature conditions to which the mites had been exposed before the experiments. Evidence of an avoiding reaction by many mites to extreme temperature conditions in the gradient provides a partial explanation for the seasonal change in the distribution of mites in the soil profile.