ABIOTIC FACTORS AFFECTING THE DEVELOPMENT OF FLEAS (SIPHONAPTERA) OF CALIFORNIA GROUND SQUIRRELS (RODENTIA: SCIURIDAE) IN SOUTHERN CALIFORNIA, USA

Abstract:
The California ground squirrel, Spermophilus beecheyi (Richardson), is a reservoir of bubonic plague throughout most of its range. Three species of fleas occur on these animals; Oropsylla montana (Baker), Hoplopsyllus anomalus (Baker), and the sticktight flea, Echidnophaga gallinacea (Westwood). Despite the importance of these fleas to plague transmission, there is only limited information regarding their biology, ecology, and how this might influence their control. Wild squirrels were deparasitized, tested for disease, and individually maintained in tub-style guinea pig cages. A novel nesting-box was designed to collect flea eggs without removing or handling the animal. Eggs were reared to adults on artificial media exposed to different temperature and relative humidity combinations similar to those reported from inside squirrel burrows. Survivorship from egg-to-adult varied for each flea species under different conditions. Results with H. anomalus and E. gallinacea suggest that these are more xeric-adapted species than O. montana. Average egg hatch of H. anomalus and E. gallinacea was substantially reduced at 31.5% RH and no larvae survived more than 48 hrs at less than 55% RH. In contrast, O. montana was highly susceptible to desiccation when reared at less than 75% RH, with none surviving at less than 65% RH. The developmental time of all species increased at lower temperatures and RH. Our initial results corroborate reported seasonal shifts in adult flea abundance on wild squirrels.