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°C) was shown to favor direct development, producing infective larvae, while high temperature (25°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°C or a 6-h temperature stimulus at 25°C. Moreover, eggs were not susceptible to the cold-temperature stimulus of 15°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.