Temperature and the hygropreference of the Arctic Collembolan Onychiurus arcticus and mite Lauroppia translamellata

The hygropreference of adult Onychiurus arcticus (Tullberg) was investigate d over 2 h at 0, 10 and 20 degrees C, along humidity gradients (12-98% RH) established using different salt solutions. At all temperatures 0. arcticus preferred the highest humidity (98% KH). At 0 and 20 degrees C, saturated conditions were preferred to 98% RH. The hygropreference of the mite Laurop pia translamellata (Willmann) was also assessed at 20 degrees C, and no cle ar RH preference was observed. This species survived the loss of 24.9 +/- 2 .1% of its initial water content when held for 24 h at 20 degrees C and 12% RH. A range of assays designed to eliminate the influence of thigmotactic behaviour and population clumping pen-nit exclusion of these factors as bei ng responsible for the observed results. The mean initial water content of O. arcticus samples (71.7 +/- 10.9, 73.4 +/- 4.0 and 73.8 +/- 23.5% at 0, 1 0 and 20 degrees C, respectively) did not differ significantly between temp eratures, indicating that the results were not influenced by differences in initial hydrated state. The percentage water loss of individuals within th e gradient increased with temperature, and differed significantly between r egimes. The ecological significance of the observed humidity preferences ar e discussed.