Biology as an Aid to the Identification of Two Closely Related Species of Ticks of the Genus Ornithodoros

Abstract

Recent studies on several lots of ticks from California, identified on a morphologic basis as Ornithodoros turicata, but shown biologically to be 0. parkeri cast doubt on some of the published records for 0. turicata from this state. The type specimens of 0. turicata (Duges), 1876, were described from Guanajuato, Mexico; and the type specimens of 0. parkeri Cooley, 1936, were described from Wyoming, U.S.A. Geographically, 0. turicata has a southern distribution while 0. parkeri has a northern distribution. Morphologically, the two species differ mainly in the size and distribution of the mammillae and in the relative lengths of the hypostomes (Cooley and Kohls, 1944). In the laboratory they interbreed and produce fertile progeny (Davis, 1942), but otherwise they differ widely, biologically. As listed by Cooley and Kohls (1944), 0. turicata was first recorded from California by Banks from San Diego County in 1908. Further listings by these authors are from Riverside County, Harbinson (1935); Madera County, Kelley (1939); and Alameda County, Holdenried (1940). An adult tick found on a man in Merced County was described as O. wheeleri n. sp. by Mclvor (1937). Hoping to obtain more specimens of this new species, the writer collected a large number of ticks from Kern and Fresno Counties which were identified as 0. turicata. Following biologic studies, which indicated that the ticks were 0. parkeri and not 0. turicata, a further morphologic study was made by Dr. R. A. Cooley and Dr. Barbara C. Mclvor of undoubted 0. turicata and 0. parkeri; of the California specimens collected by the writer; and of the newly named 0. wheeleri; and it was agreed that all ticks from the area were 0. parkeri. These ticks were then listed as 0. parkeri, and 0. wheeleri was placed in synonymy (Cooley and Kohls, 1944). In 1943, the writer collected ticks in the same area as Holdenried's 1940 collection. These ticks were also identified as 0. turicata by Dr. R. A. Cooley. In 1948, specimens received from Yolo County were identified as 0. parkeri by Glen M. Kohls of this Laboratory. These ticks were then studied biologically and the results confirmed the identification. This study was based on only one of the criteria to be mentioned. The tests were as follows: Ten of the California ticks, and ten 0. parkeri (Washington stock) engorged on a white mouse infected with an Idaho 0. parkeri strain of spirochetes. The ticks were subsequently tested for transmission by feeding individually on white mice. There was 60 per cent transmission by the California ticks and 90 per cent transmission by the Washington 0. parkeri. Similarly, ten of the California ticks and ten 0. turicata (New Mexico stock) engorged on a mouse infected with 0. turicata