Published online by Cambridge University Press: 31 May 2012
Most of the relative humidity gradients used in ethological studies of insects are of the alternative type in which a choice between only two relative humidities is possible (Perttunen, 1953; Wigglesworth, 1941). Sometimes, during investigations of behaviour and distribution of insects, it may be desirable to know the humidity preferred when insects are exposed to an environment in which a number of different humidities prevail in a definite, specified range. In some cases both the range of humidities in a gradient and the values of the extreme humidities apparently affect the preference exhibited by certain arthropods (Perttunen, 1953; Bursell and Ewer, 1950; Lees, 1943). The circular apparatus described here allows the simultaneous production of two identical gradients, one in each half of the circle.