A Comparative Study of Rodent and Burrow Flea Populations. ∗

Abstract

An area located at Calaveras Dam, Alameda County, California, previously determined to be heavily populated with ground squirrels [Citellus beecheyi (Richardson)], was selected for field study of (1) the correlation between flea populations existing at squirrel burrow openings and of flea populations on the rodent hosts, and of (2) the seasonal species composition of these populations. One portion of this area was set aside for the study of the fleas at the openings of the burrows, and a contiguous and ecologically similar portion was utilized for the study of fleas taken directly from their hosts.

Fleas at the burrow openings were collected from pieces of cotton batting placed in each burrow mouth. Thirty burrows were set aside for these studies, divided into 3 groups of 10 burrows each and approximately equally distributed as to direction of exposure, amount of exposure, surrounding cover crop and topography. Collections were made at approximately weekly intervals from April 29, 1940, to October 23, 1940, as shown in Graph 1, and they were made in regular rotation among the 3 sets of burrows in order not to influence unduly the population densities by repeated collections. In the same period and also at approximately weekly intervals, as shown in Graph 2, ground squirrels were trapped alive, lightly anesthetized with chloroform, and thoroughly combed to remove all fleas. At each burrow collection temperatures were taken at points 1 foot within the mouth of the burrow and 6 feet above the ground. All fleas collected were mounted and identified; of approximately 7500 fleas collected only about a dozen belonged to species other than Diamanus montanus (Baker) or Hoplopsyllus anomalous (Baker).

As shown in Graphs 1 and 2, Diamanus montanus was markedly-predominant in the flea population from April 29 to June 28 and Hoplopsyllus anomalus was markedly predominant from July 11 to October 14. No correlation could be detected between either atmospheric or burrow temperatures and flea indices other than that Diamanus montanus was predominant while the mean temperature was below 75°F and Hoplopsyllus anomalus was predominant while the mean temperature was above 75°F.