Five New Fleas of the Genus Thrassis Jordan, 1929 (Ceratophyllidae: Siphonaptera), a Genus of Known Importance in Plague Transmission

Abstract

Several members of the genus Thrassis serve to disseminate and maintain plague among certain groups of wild rodents in the western United States. Laboratory experiments (Eskey and Haas, 1940) show that several species have the ability to transmit plague. Macchiavello (1954) calculates the vector efficiency* of T. pandorae Jellison to be 1.10. Prince (1943) found that T. bacchi bacchi (Rothschild) had a ratio** of 0.10 transmissions to the 40 fleas used. Other species have been shown to have the following vector efficiencies: T. francisi (Fox) 0.09 and T. acamantis ssp., T. stanfordi Wagner and T. arizonensis ssp., all 0.04. (After Eskey and Haas, 1940). T. petiolatus (Baker) was laboratory-infected (Eskey and Haas, 1940) and naturally infected (Jellison, 1937). In addition to the above experimental findings, T. bacchi pansus (Jordan) T. b. gladiolis (Jordan) and T. fotus (Jordan) were reported by the San Francisco Field Station as being naturally infected. In surveys conducted over western United States by the San Francisco Field Station from 1936 to 1949 for determining the presence of plague in fleas, the genus Thrassis was more often in positive pooled inoculations than other genera. Most Thrassis collected and tested in the past have come from the larger rodents (Sciuridae). However, Thrassis of smaller rodents may play an important role in plague transfer. As an example T. bacchi johnsoni (Hubbard) has been shown to have a very high vector efficiency (Kartman and Prince, 1956). It occurs in great numbers on Lagurus curtatus ssp., the sagebrush vole, in eastern Washington and is probably the most important flea in maintaining plague in this rodent population.