Comparison of Lengths of Outer Opisthosomal Setae of Male Psoroptic Mites Collected from Various Hosts

Abstract

Sweatman (1958, Can. J. Zool. 36: 905-929) reported that the location of Psoroptes mites on the host animal, i.e., ear or body, was one of the determining factors for separation of the psoroptic mites into species. He also confirmed the observation of Hirst (1922, Brit. Museum Nat. History, Econ. Ser. No. 13) that the setae on the opisthosomal lobes of the adult male were of diagnostic value. Sweatman concluded that the outer opisthosomal setae (OOS) or 14 setae (Fain, 1970, Rev. Zool. Bot. Afr. LXXXI: 95-100) was the primary factor in separation of the species and that Psoroptes ovis and P. bovis were the same species even though the host animals were different. Observations in our laboratory have indicated a wide overlap in the lengths of the 14 setae of adult males of psoroptic mites in our collections from various hosts and geographic locations. Sweatman also noted this overlap. The objective of our study was to compare lengths of the 14 setae of male psoroptic mites collected from various hosts from different geographic locations and to determine the reliability of the length of 14 setae as a characteristic to differentiate between species. Most of the mites studied were collected in recent years; however, additional mounted specimens were obtained from the collection of the Parasite Research Laboratory, Albuquerque, New Mexico, now located at Kerrville, Texas, as the Scabies and Mange Mite Research Unit of the U.S. Livestock Insects Laboratory. Mites collected from the ears of rabbits, goats, mule deer, white-tail deer, and ibex were considered to be P. cuniculi. Mites collected from the body of cattle and domestic sheep were considered to be P. ovis. Mites collected from bighorn sheep were considered to be P. ovis or P. cervinus. The mites were mounted on glass slides in Hoyer's medium for measurements. Setal length was measured in micrometers (,um) with a Zeiss microscope equipped with differential interference-contrast, x 10 eye pieces, a x 40 objective, and a calibrated measuring reticule. Each 14 seta measured was considered an observation. Data were transformed to log 10 values and analyzed by one-way analysis of variance (ANOVA) for unequal sample sizes (Sokal and Rohlf, 1969, W. H. Freeman and Co., San Francisco, California, 776 p.). The differences between the means of the lengths of the 14 setae from the mites from various collections were analyzed by the Student-Neuman-Keuls (SNK) test for unequal sample sizes (Sokal and Rohlf, 1969, loc. cit.). The log 10 mean values were converted to their antilog value before being reported in the test. The lengths of the 14 setae of the adult male mites of Psoroptes spp. collected from the various hosts and geographic locations were compared statistically (Table I). The lengths of the 14 setae of mites (Mission strain) collected from sheep, of mites from bighorn sheep (Idaho), and of mites from cattle (Brazil) were all significantly different (P < 0.05) from the lengths of 14 setae from all other collections of mites regardless of host, body location, or geographic location. There were many differences within the same host animal. For example, the lengths of 14 setae from mites collected from rabbits from New Mexico, Kerrville, and England were all significantly different from each other. The lengths of 14 setae of mites collected from goats in Texas and New Mexico were significantly different from each other. The lengths of 14 setae of mites collected from cattle in the USA (Albuquerque, Kerrville, Hereford, and Colorado) were significantly different (P < 0.05) from those of mites collected from Holstein cattle from Brazil. The lengths of 14 setae from mites of the Mission strain from sheep were significantly different from those of all other strains of mites from sheep at Albuquerque, England, and South Africa. The lengths of 14 setae from mites of the mixed strain and the ADP strain were significantly different from those of the Beltsville-2 strain and England strain also. There was no consistency between the