Plague vector studies. II. The role of climatic factors in determining seasonal fluctuations of flea species associated with the California ground squirrel.

Abstract

Studies were conducted on California ground squirrels confined in O.4-ha electrically-fenced fields to determine the effects of physical factors in the environment on seasonal fluctuations in the population densities of Hoplopsyllus anomalus, Diamanus montanus and Echidnophaga gallinacea. The summer-breeding species, H. anomalus and E. gallinacea, were greatly restricted in their reproductive activities in the experimental field where moisture was supplemented to keep the soil moist to 1 m in depth; the winter-breeding species, D. montanus, was much more reproductively active during the summer in the experimental area where the soil was kept moist. A total of 46,962 fleas was collected from 468 ground squirrels during the course of this study. Trained ferrets were used to pull electrical cables into the ground squirrel burrows to enable the operators to record the relative humidities and temperatures existing at various levels in the burrow systems.