Parasites of New World Microtus

Abstract

The objective of this review is to bring together and summarize the diverse literature on parasites of New World Microtus, to summarize life cycles of the ectoparasitic fauna, and to put the different groups of parasites into a biological perspective. The literature on parasites of Microtus contains over 485 primary references covering the 91-year period from 1894 to 1984. However, of the 26 species of New World Microtus now recognized, parasite data exist for only 16 species. Most of the data available are for six of the most widely distributed species, Microtus californicus, M. longicaudus, M. montanus, M. ochrogaster, M. pennsylvanicus, and M. pinetorum. The ectoparasites on Microtus belong to the orders Acari (mites and ticks), Anoplura (suckling lice), Coleoptera (beetles), Diptera (flies), and Siphonaptera (fleas). Twelve families of mites are known from Microtus. These range in size from minute demodicids that live within hair follicles and sebaceous glands to the large, active laelapids. Very little work has been done on any of the mites with the exception of chiggers (family Trombiculidae). Most groups are in need of taxonomic revision. Chiggers have been intensively studied, both taxonomically and biologically, as they are of direct medical importance to man. Eighteen species of ticks have been reported from Microtus. Several species of ticks carried by Microtus are responsible for diseases that affect man, and the systematics and ecology of these vectors have received much attention. Only two species of sucking lice are true parasites of Microtus, although a few other species have been reported in the literature as being found on Microtus. The systematic relationships of the lice are well understood; however, little work has been done on their biology. Lice have been reported on only 12 species of Microtus; the absence of lice on several species (for example, M. chrotorrhinus) has not been explained. Parasitic beetles belonging to two families have been found only occasionally on Microtus. It is likely that they are regularly associated with Microtus, living primarily within the nest and hence seldom encountered. Two families of parasitic flies are known from Microtus. Both bot flies and flesh flies are uncommon parasites of Microtus, and if found in high numbers may have an adverse effect upon the host. Seventeen genera of fleas regularly parasitize Microtus in North America, and 26 other genera are reported as of accidental occurrence. A tremendous body of literature exists on the systematics and ecology of fleas, especially with respect to bubonic plague. However, little work has been undertaken on the effects of fleas or the diseases they transmit on Microtus. Most species of Microtus have several species of fleas; more than one species may be present on an individual host with additional species being restricted to the nest. Endoparasites belong to the Acanthocephala, Cestoda, Nematoda, and Trematoda. Only two species of acanthocephalan have been found parasitizing Microtus. Several species of cestodes) nematodes, and trematodes have been reported from Microtus, and it is certain that this list will increase with additional study. A briefly annotated list of the endoparasites on New World Microtus is appended.