ABCDEFGOrchopeas leucopus(Baker)00533137610Orchopeas howardii(Baker) =O. wickhami(Baker)0000010Nosopsyllus fasciatus(Bosc)0000010Epitedia wenmanni(Rothschild)0009020Rectofrontia fraterna(Baker)0000010Corrodopsylla hamiltoni(Traub)47800000Ctenophthalmus pseudagyrtesBaker0380042553Peromyscopsylla scottiI. Fox0006000——————————————Total number examined341334355741421
[E]The numbers represent the percentage of each species which was parasitized by fleas. The mammals were collected at Lawrence, Douglas County, Kansas, between October, 1945, and June, 1946. These data are entirely from snap-trapped animals with the exception of those fromMicrotusandPitymyswhich are from both snap-trapped and live-trapped animals.
[E]The numbers represent the percentage of each species which was parasitized by fleas. The mammals were collected at Lawrence, Douglas County, Kansas, between October, 1945, and June, 1946. These data are entirely from snap-trapped animals with the exception of those fromMicrotusandPitymyswhich are from both snap-trapped and live-trapped animals.
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.
Epitedia wenmanniwas found on the white-footed mouse (Peromyscus leucopus) and only rarely on the prairie vole.Corrodopsylla hamiltoniwas taken only from the two kinds of shrews (Blarina brevicaudaandCryptotis parva). Fleas on shrews may have a well-developed host preference. At any rate, Elton, Baker, Ford, and Gardner (1931) found thatDoratopsylla dasycnemusrarely strayed from its normal host (Sorex araneus) to other small mammals.Peromyscopsylla scottiwas 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.
Orchopeas leucopuswas 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 nemoralisandMicrotus ochrogaster).Ctenophthalmus pseudagyrtesis 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 intable 6; and one flea (Rectofrontia fraterna) may prove to be a common nest parasite.Orchopeas howardiiis common on tree squirrels (Sciurus nigerandS. carolinensis).Nosopsyllus fasciatusis a cosmopolitan flea onRattus norvegicus.Rectofrontia fraternawas 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. IfCtenophthalmus pseudagyrtesacted as the intermediate host of a disease-causing organism, an epizootic fromMicrotus ochrogastermight be transmitted toPitymys nemoralisor toSigmodon hispidusorBlarina brevicauda. There are several other such potential bridges for blood parasites. Althoughtable 6does 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 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 toHoplopleura hirsutaFerris, and the two species ofPeromyscuswere parasitized byHoplopleura hesperomydis(Osborn).
The writer collectedHoplopleura acanthopusfromMicrotus californicusat Calaveras Dam, Alameda County, California, and fromM. pennsylvanicusat Ithaca, Tompkins County, New York. Elton,Ford, Baker, and Gardner (1931) recorded this same species fromM. argestisin England.
Lice on the prairie vole are the same species as those found on other species ofMicrotusin 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.
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 intable 7.
The following comments can be made concerning the specificity and geographic ranges of several species of mites:
Liponyssus occidentalisEwing was found only onCryptotis 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 intable 1, it was found to be a common parasite onPitymys pinetorumat Point Abino, Welland County, Ontario. Elton, Ford, Baker and Gardner (1931) found this same mite onApodemus sylvaticusandClethrionomys glareolusin England.
Atricholaelaps glasgowi, like the preceding species, was one of the commoner mites on the prairie vole. It was found also onPitymys pinetorumat Point Abino, Welland County, Ontario; onMicrotus pennsylvanicusat Ithaca, Tompkins County, New York; and onM. californicusat Calaveras Dam, Alameda County, California.
Atricholaelaps sigmodonioccurred only on the cotton rat.
Laelaps kochiwas less commonly found thanEulaelaps stabularisandAtricholaelaps glasgowi. In Kansas the prairie vole and the cotton rat were hosts toLaelaps kochi, and it occurred onMicrotus pennsylvanicusat Ithaca, New York, and onM. californicusat 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 wereAscoschöngastia brevipes(Ewing); other species may be involved.
Listrophoridae was represented on the prairie vole by a species ofMyocoptesand a species ofListrophorus. 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.
Two kinds of ticks were found. One adult specimen ofIxodes sculptusNeumann 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 ofDermacentor 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 aquaticusB:Cryptotis parvaC:Blarina brevicaudaD:Peromyscus maniculatusE:Peromyscus leucopusF:Sigmodon hispidusG:Microtus ochrogaster
ABCDEFGAscoschöngastia brevipes(Ewing)........XXXLiponyssus occidentalisEwing..X..........Eulaelaps stabularis(Koch)XXX..X..XAtricholaelaps glasgowi(Ewing)......X....XAtricholaelaps sigmodoniStrandtmann..........X..Laelaps kochiOudemans..........XXMyocoptessp.............XListrophorussp.............X
[F]These data are from material collected at Lawrence, Douglas County, Kansas.
[F]These data are from material collected at Lawrence, Douglas County, Kansas.
Each prairie vole was assigned to one of three age classes (juvenile, subadult, or adult) principally on the basis of weight, but partly on the quality and color of the pelage. The three age classes are characterized in table 8.
Table 8.Characters of Juvenile, Subadult, and Adult Prairie Voles
JuvenileSubadultAdultLess than 21 grams21-38 grams38 grams or moreWeight usually less than 20 gramsAverage weight 30-32 gramsAverage weight 40-45 gramsEntire pelage dullPelage of rump dull; rest of pelage glossyPelage usually entirely glossy (rump sometimes dull)Dorsal color blackDorsal color grizzled except on rumpEntire dorsal color grizzled except sometimes on rump
Hamilton (1941:4) found forMicrotus pennsylvanicusthat macroscopic tubules of the cauda epididymis were an indication of fecundity. By noting the size of the tubules (whether macroscopic or not) and by making smears from them in approximately every 25th male caught, I found that the presence of sperm was positively correlated with large-sized tubules of the cauda epididymis inMicrotus ochrogaster. Inferentially, males with sperm were fecund.
There is a relationship almost positive between the size of the tubules of the cauda epididymis and the length of the testes. Testeslonger than 7 mm. have macroscopic tubules in the cauda, and in testes shorter than 7 mm. these tubules cannot be seen with the naked eye, Hamilton (1937b) found that inM. pennsylvanicustestes smaller than 8 × 4 mm. did not contain sperm. The testes of the prairie vole descend into the scrotum in the breeding season. In the two winter months, when the voles did not bring forth young, the testes decreased in size (seefigure 3) and were withdrawn into the body cavity. The presence of the testes in the body cavity does not mean that a vole is not in breeding condition, for many specimens with abdominal testes were fecund.
The females were considered to be fecund if they were gravid, or if there were placental scars in the horns of the uteri.
Figure 2. Fecundity of Prairie Voles by Months. Adults and Subadults are Considered Together.Figure 2. Fecundity of Prairie Voles by Months. Adults and Subadults are Considered Together.
Figure 3. Seasonal Changes in the Length of Testes.Figure 3. Seasonal Changes in the Length of Testes.
The number of mammae characteristic of a species of vole may be a rough guide to the average size of a litter for that species. The prairie vole has fewer mammae (three pairs) than some other voles in North America, and might, therefore, be expected to have smaller litters. Fifty-eight gravid females ofMicrotus ochrogasterexamined by me had an average of 3.4 embryos each; the number of embryos ranged from one to seven. Hamilton (1936a) gave 5.07 as the average number of young per litter inM. pennsylvanicus. Hatfield (1935) stated thatM. californicushas an average of 5.7 young in a litter. Bothpennsylvanicusandcalifornicusnormally have four pairs of mammae. The expectation as to the size of the litter seems to be realized. In the prairie vole one pair of mammae is pectoral and two pairs are abdominal. Usually a lactating vole showed evidence of only the abdominal mammae having been in use.
The size of litters was found to vary with the season of the year (seetable 9). Gravid females were collected in every breeding month except September.
Table 9.Average Size of Litters of Microtus ochrogaster by Months[G]
Jan.Feb.Mar.Apr.MayJuneJulyAug.Sept.Oct.Nov.Dec.02.83.93.23.43.12.83.0..3.22.60..(4)(10)(6)(8)(9)(5)(2)..(5)(5)..
[G]These months are from October, 1945, until August, 1946. The numbers in parentheses indicate the number of gravid females collected each month.
[G]These months are from October, 1945, until August, 1946. The numbers in parentheses indicate the number of gravid females collected each month.
Table 9 shows that the prairie vole produced the largest litters in March. A comparison oftable 9withfigure 2shows that the largest litters were produced at the height of the breeding season. Baker and Ransom (1933), studyingMicrotus agrestis, also found that larger litters were characteristic of the height of the breeding season; and that at the beginning and at the end of the breeding season the litters averaged smaller.
The size of litters varied also with the age of the female. To place a gravid female in its proper age class, the weight of the embryos was subtracted from the total weight, and the remaining weight was used as the body weight. The average size of the litters of 14 subadults was 2.9, and in 35 adults it was 3.4. Hatfield (op. cit.) found that the younger females ofM. californicusgave birth to smaller litters than did the adults.
Not included in either of the above analyses are nine gravid females collected in November in a pasture watered by an artesian spring in Atchison County, Kansas. In this pasture there was a high concentration of prairie voles, and the percentage of fecundity was much higher than in Douglas County at the same time. In November only 29 per cent of the female prairie voles in Douglas County were fecund, as against 59 per cent in Atchison County. The average number of embryos of these nine voles was 4.1. Data from Atchison County are not included intable 9.
In October, 1945, when this study was begun, the prairie vole was bringing forth young. In the winter of 1945-'46 at Lawrence, Kansas, there was a cessation of reproduction. The reproductive activity was measured in terms of the fecundity of the subadults and the adults of both sexes.Figure 2suggests that the decline was most marked in December and January; no gravid females were collected in these two months, although two females trapped in the first week of December were lactating. In October, November, and December, 85 per cent of the breeding females were adults. In October, 85 per cent of the adult females were fecund, and in November, this figure was 80 per cent. Reproduction at this season, in the females, it appears, was largely a function of the adults. The proportion of adults to the rest of the population was calculated for each month; and the monthly changes in relative numbers of adults is shown infigure 4. In November, December, and January there was a scarcity of adult voles in the population. The autumnal decline in reproduction occurred simultaneously with the disappearance of these adults, and is thought to have been largely a result of it.
Reproductive activity began in February; and in this month one-third of the females contained embryos, and 90 per cent of the males were fecund. Reproduction reached its height in March when fecundity for the females and males was 77 per cent and 100 per cent respectively. In April both sexes showed signs of being less productive,and still later in the spring the percentage of fecundity remained at slightly over 65 for both sexes, this figure being higher for the males than for the females for any one month. From January to February there was a 30 per cent increase in the percentage of adults in the population; and for this period, there was a 33 per cent increase in the fecundity of both males and females. In February, 80 per cent of the fecund females were adults. The breeding in the late winter, as in the fall, is thought to depend upon the percentage of adults in the population. Hamilton (1937b) noted a similar correlation between winter breeding and dominance of adults inMicrotus pennsylvanicusin New York. Fisher (1945) found that the prairie vole continued to breed throughout the winter of 1943-'44 in Missouri; in such a case, one would expect to find a large proportion of adults in the population.
Figure 4. Seasonal Changes in the Numbers of Adults in Relation to the Total Population of Prairie Voles.Figure 4. Seasonal Changes in the Numbers of Adults in Relation to the Total Population of Prairie Voles.
Throughout the winter of 1945-'46, at Lawrence, the majority of males were fecund; but fecundity in the females was much less, and in January, no females showed signs of reproductive activity. From this it appears that the females, not the males, limit the breeding season of this species.
In the eleven month period, October, 1945, until August, 1946, in northeastern Kansas, more than five hundred specimens of the prairie vole (Microtus ochrogaster) were examined in the flesh; and forty free-living voles were examined 157 times—an average of slightly less than four times each.
There is a complete molt from juvenal to subadult pelage, and one from subadult to adult pelage. These molts require three weeks each. Subsequent molts are irregular and extend over longer periods of time.
This vole, in summer, inhabits areas of grass, clover, and alfalfa. In winter, habitats with some woody growth may be sought. Twenty-two kinds of plants were found to be used for food. Although most of these were succulent plants, seeds and small woody stems were sometimes eaten. The prairie vole, like some other species ofMicrotus, lays away stores of food, usually underground; the maximum quantity found in one cache was two gallons.
Nine other species of small mammals occur in the same habitat with the prairie vole, and frequently use its runways. The vole makes a network of paths through the grass, and constructs its own burrows which lead to its nests and food stores. Each of fifteen nests found were underground. Most, if not all, of the underground tunnels are dug when the soil is moist, not when the soil is dry.
The commonest flea on the prairie vole isCtenophthalmus pseudagyrtes; it averages 1.9 (for subadult voles) to 3.4 (for adult voles) per individual vole. Other fleas on this vole areOrchopeas leucopus,Orchopeas howardii,Nosopsyllus fasciatus,Epitedia wenmanni, andRectofrontia fraterna. The two species of fleas which were actually common on the vole (C. pseudagyrtesandO. leucopus), parasitized also some other small mammals which lived in the same habitat as the vole. One species of sucking louse (Hoplopleura acanthopus) and two kinds of mites (Laelaps kochiandAtricholaelaps glasgowi) which occur on the prairie vole in Kansas, occur also onMicrotus californicusin California and onM. pennsylvanicusin New York. Only three ticks (1Dermacenter variabilisand 2Ixodes sculptus) were found on the prairie vole.
Fifty-eight gravid females had an average of 3.4 embryos. Litters at the height of the breeding season are larger than those at the beginning and at the end of the breeding season. Reproduction inMicrotus ochrogasterceased in December, 1945, in northeastern Kansas, and the first evidence of reproduction in 1946 was observed in February.
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Transmitted August 13, 1946.
21-6957
Page136, Table 3, under Compositae: changed Loctuca to Lactuca(_Loctuca scariola_)and changed artemsiifolia to artemisiifolia(_A. artemsiifolia_)Page139: changed trappd to trapped(from live-trapped and some snap-trappd voles.)and changed rate to rat(the prairie vole and the cotton rate)Page141: changed Almeda to Alameda(at Calaveras Dam, Almeda County, California,)Page142: kept section heading: Mites (Acarina except Ixodoidea)(the TOC lists the variation Acari instead of Acarina)and changed Almeda to Alameda(at Calaveras Dam, Almeda County, California.)Page143: changed tridecimlineaus to tridecimlineatus(ground squirrel (_Citellus tridecimlineaus_) at Lawrence.)Note: Another spelling variation is: tridecemlineatus.Page146: changed table 2 to table 9(A comparison of table 2 with figure 2 shows that the largest)Page143: kept spelling variation: Dermacentor variabilisPage149: kept spelling variation: Dermacenter variabilisPage150: changed LITERAURE to LITERATURE(LITERAURE CITED)and kept spelling variation: agrestris, being a reference citation(1933. Factors affecting ... field mouse (_Microtus agrestris_)).