Effect of temperature on the development of free-living stages of Strongyloides ratti.

In the genus Strongyloides, larval development external to the host is known to be markedly affected by a variety of environmental factors. This investigation focuses on the effect of temperature on Strongyloides ratti. Low temperature (15 degrees C) was shown to favor direct development, producing infective larvae, while high temperature (25 degrees C) favored indirect development, producing free-living females and males. Different courses of development were brought about by either a 16-h temperature stimulus at 15 degrees C or a 6-h temperature stimulus at 25 degrees C. Moreover, eggs were not susceptible to the cold-temperature stimulus of 15 degrees C, while newly hatched larvae were. The results indicate that the developmental course of S. ratti larvae external to the host is determined at a relatively early stage before the first molt.