EXTERNAL PARASITES

The pelage of prairie voles, pine mice, deer mice, and shrews forms a habitat for many kinds of parasitic arthropods. The fleas, lice, and mites from the prairie vole were collected, counted, and identified. The ectoparasites from the other small mammals living in the same habitat as the prairie vole were also considered. Some ectoparasites begin to leave the host when it dies, and any counts of ectoparasites made from snap-trapped voles may fall short of the number which was on the animal when it was alive. The average number of fleas recorded from live voles exceeds that found on snap-trapped voles (see table 4). The numbers of lice and mites were estimated, but selected voles were examined to obtain absolute numbers of these kinds of ectoparasites.

The fleas, lice, and mites were mounted on one inch by three inch glass slides; the ticks were preserved in 70 per cent alcohol. Dr. E. W. Baker identified the mites; Dr. R. A. Cooley and Dr. Glen M. Kohls, the ticks; Dr. G. W. Wharton, the chiggers; and Dr. Gordon F. Ferris, the lice. To each of these gentlemen I am grateful. The fleas were identified by myself.

Fleas (Siphonaptera)

The information on the average numbers of fleas on voles was obtained from live-trapped and some snap-trapped voles. Fleas were counted only on voles which were removed from the traps within twenty-four hours after the traps had been last examined. The average numbers of fleas found on prairie voles in this study are given in table 4.

Table 4. Average Numbers of Fleas on Prairie Voles[C]

SubadultsAdults

Live-trapped voles1.9 (73)3.4 (29)

Snap-trapped voles1.1 (26)1.3 (27)

Table 5 shows the average degree of infestation for ten months of an eleven month period. The monthly averages for the most part show no variations. The latter half of February provides an exception in that a series of 22 snap-trapped voles and 11 live-trapped voles taken at that time had on the average, 9.7 and 5.3 fleas respectively. Pine mice (Pitymys nemoralis) occurred in small numbers in the area where Microtus ochrogaster was live-trapped, and Ctenophthalmus pseudagyrtes was the flea found to be common on both of these voles.

Table 5.—Monthly Averages of Fleas on Prairie Voles

Jan.Feb.Mar.Apr.MayJuneJulyAug.Sept.Oct.Nov.Dec.

.65.15[D]...31.81.41.7...1.122

(6)(11)(6)...(6)(88)(26)(6)...(8)(14)(2)

Some fleas have a habitat preference as well as a host specificity. As voles from different areas were examined, different kinds of fleas were encountered. A population of free-living voles under observation on the Campus at Lawrence was parasitized only by Ctenophthalmus pseudagyrtes. From 90 prairie voles collected in a field of clover 4 miles northwest of Lawrence, the only species of flea recovered was Orchopeas leucopus. In both places the prairie vole was the most common mammal, but in the field of clover three deer mice (P. maniculatus) also were trapped. In a third field, one mile west of Lawrence, the prairie vole was host to both the above mentioned fleas. Here both the prairie vole and the cotton rat (Sigmodon hispidus) were common.

The host distribution of fleas on seven small mammals which lived in the same habitats as the prairie vole is given in table 6.

Table 6.—Frequency of Occurrence of Fleas on Seven Species of Small Mammals[E]

Column headings: A: Cryptotis parva B: Blarina brevicauda C: Peromyscus maniculatus D: Peromyscus leucopus E: Sigmodon hispidus F: Microtus ochrogaster G: Pitymys nemoralis

ABCDEFG

Orchopeas leucopus (Baker)00533137610

Orchopeas howardii (Baker) =

O. wickhami (Baker)0000010

Nosopsyllus fasciatus (Bosc)0000010

Epitedia wenmanni (Rothschild)0009020

Rectofrontia fraterna (Baker)0000010

Corrodopsylla hamiltoni (Traub)47800000

Ctenophthalmus pseudagyrtes Baker0380042553

Peromyscopsylla scotti I. Fox0006000

——————————————

Total number examined341334355741421

It is seen that some fleas are rather specific in their choice of hosts, and that others are commonly found on two or more small mammals in the same habitat. In each of these groups there are fleas which have a habitat preference, that is to say, the flea lives on the host when the host lives in a given habitat, but is absent when the host lives in another habitat.

Group 1: Fleas with a Host Preference

Epitedia wenmanni was found on the white-footed mouse (Peromyscus leucopus) and only rarely on the prairie vole. Corrodopsylla hamiltoni was taken only from the two kinds of shrews (Blarina brevicauda and Cryptotis parva). Fleas on shrews may have a well-developed host preference. At any rate, Elton, Baker, Ford, and Gardner (1931) found that Doratopsylla dasycnemus rarely strayed from its normal host (Sorex araneus) to other small mammals. Peromyscopsylla scotti was taken from the white-footed mouse (Peromyscus leucopus), and had a habitat preference also. It was found only on those white-footed mice which were trapped in the woodlands at various places in Douglas County; white-footed mice which were trapped in areas of brush were free of this parasite.

Group 2: Fleas Commonly Found on Two or More Kinds of Small Mammals

Orchopeas leucopus was an outstanding example of this group. It was the most common flea on the deer mouse, the white-footed mouse, and the cotton rat. In certain areas it was common on the two voles (Pitymys nemoralis and Microtus ochrogaster). Ctenophthalmus pseudagyrtes is the most abundant flea on the two kinds of voles and on the large shrew (Blarina brevicauda), and was found sparingly on the cotton rat.

Several kinds of fleas do not belong in either of the above groups. Some fleas were accidental strays from mammals not included in table 6; and one flea (Rectofrontia fraterna) may prove to be a common nest parasite. Orchopeas howardii is common on tree squirrels (Sciurus niger and S. carolinensis). Nosopsyllus fasciatus is a cosmopolitan flea on Rattus norvegicus. Rectofrontia fraterna was taken once from a prairie vole. Since the only specimens in the University of Kansas Entomological Collections are from "mouse nests," this flea may be found to be a nest inhabiting parasite.

Some fleas are possible bridges by which a blood parasite could be transmitted from one kind of a mammal to another. If Ctenophthalmus pseudagyrtes acted as the intermediate host of a disease-causing organism, an epizootic from Microtus ochrogaster might be transmitted to Pitymys nemoralis or to Sigmodon hispidus or Blarina brevicauda. There are several other such potential bridges for blood parasites. Although table 6 does not prove that individual fleas wander from one host to another, the frequency with which the several kinds of fleas are removed from live mice suggests that the fleas occasionally do so.

Lice (Anoplura)

Lice collected from the prairie vole were all of one species, Hoplopleura acanthopus (Burmeister). Of 59 voles examined for the presence of lice, 33 were found to be parasitized; the 59 voles had an average of 3.4 lice each. Other mice which used the same runways as the prairie vole had their own species of Anoplura. The cotton rat was host to Hoplopleura hirsuta Ferris, and the two species of Peromyscus were parasitized by Hoplopleura hesperomydis (Osborn).

The writer collected Hoplopleura acanthopus from Microtus californicus at Calaveras Dam, Alameda County, California, and from M. pennsylvanicus at Ithaca, Tompkins County, New York. Elton, Ford, Baker, and Gardner (1931) recorded this same species from M. argestis in England.

Lice on the prairie vole are the same species as those found on other species of Microtus in other areas, but since Anoplura of the prairie vole do not parasitize the cotton rat, the white-footed mouse, and the deer mouse, this host specificity of lice makes it unlikely that lice would carry blood parasites from the prairie vole to any of the latter named rodents.

Mites (Acarina except Ixodoidea)

Many of the small mammals examined in this study had mites, some of which were collected and identified. Mites were collected from other species of voles in several localities in the United States and in one locality in Canada; as voles in widely separated regions are sometimes hosts to the same species of mites, these records will be presented here.

The frequency of some kinds of mites in the identified material suggests that they are more abundant than other kinds. The occurrence of mites on small mammals from Lawrence, Kansas, is presented in table 7.

The following comments can be made concerning the specificity and geographic ranges of several species of mites:

Liponyssus occidentalis Ewing was found only on Cryptotis parva.

Eulaelaps stabularis (Koch) was one of the more common kinds found on the prairie vole. This mite is rather large (about 1 mm. long) and is frequently (with the following species) seen running through the pelage of its host. In addition to the records for this species in table 1, it was found to be a common parasite on Pitymys pinetorum at Point Abino, Welland County, Ontario. Elton, Ford, Baker and Gardner (1931) found this same mite on Apodemus sylvaticus and Clethrionomys glareolus in England.

Atricholaelaps glasgowi, like the preceding species, was one of the commoner mites on the prairie vole. It was found also on Pitymys pinetorum at Point Abino, Welland County, Ontario; on Microtus pennsylvanicus at Ithaca, Tompkins County, New York; and on M. californicus at Calaveras Dam, Alameda County, California.

Atricholaelaps sigmodoni occurred only on the cotton rat.

Laelaps kochi was less commonly found than Eulaelaps stabularis and Atricholaelaps glasgowi. In Kansas the prairie vole and the cotton rat were hosts to Laelaps kochi, and it occurred on Microtus pennsylvanicus at Ithaca, New York, and on M. californicus at Berkeley, California.

Trombiculidae are commonly known by their larvae which are called chiggers or harvest mites. The white-footed mouse, the cotton rat, and the prairie vole were parasitized at Lawrence. In the winter these mites live in the ears of these small mammals, but in the summer they were found both in the ears and on the rump. Those obtained in winter were Ascoschöngastia brevipes (Ewing); other species may be involved.

Listrophoridae was represented on the prairie vole by a species of Myocoptes and a species of Listrophorus. These mites cling to the hairs of their host, and do not occur on the skin of the voles.

No evidence was seen that mites had any ill effect on the health of their hosts. No voles had scabs on the skin; and the ears were not swollen and disfigured as they sometimes are by chiggers. Although the identity of a specimen of mite could not be determined until it was mounted, a person could tell whether or not it was one of the larger, very active Laelaptidae, one of the hair-clinging Listrophoridae, or one of the tiny, orange Trombiculidae.

On July 12, 1946, three prairie voles were examined to determine the number of mites they supported. The voles were freshly caught, no one of them having been dead for more than five minutes before they were examined. These three voles had an average of 25 Laelaptidae, 22 Listrophoridae, and 53 Trombiculidae.

Six species of mites (Ixodoidea excepted) were found on the prairie vole. Four of these were collected also from other small mammals living in the same habitat as this vole. Two species of mites were found to occur on voles in New York, Kansas, and California.

Ticks (Ixodoidea)

Two kinds of ticks were found. One adult specimen of Ixodes sculptus Neumann was clinging to the head of a vole, just in front of its eye. This species of tick was taken also from the thirteen-lined ground squirrel (Citellus tridecimlineatus) at Lawrence. One nymph of Dermacentor variabilis (Say) was found attached to the scapular region of a prairie vole. Both of these specimens were taken in June.

Table 7. Host Distribution of Mites on Seven Small Mammals[F]

Column headings: A: Scalopus aquaticus B: Cryptotis parva C: Blarina brevicauda D: Peromyscus maniculatus E: Peromyscus leucopus F: Sigmodon hispidus G: Microtus ochrogaster

ABCDEFG

Ascoschöngastia brevipes (Ewing)........XXX

Liponyssus occidentalis Ewing..X..........

Eulaelaps stabularis (Koch)XXX..X..X

Atricholaelaps glasgowi (Ewing)......X....X

Atricholaelaps sigmodoni Strandtmann..........X..

Laelaps kochi Oudemans..........XX

Myocoptes sp.............X

Listrophorus sp.............X