The Discovery of Chiggers (Acarina, Trombiculidae) in the Nasal Passages of Cricetid Rodents from California, with Descriptions of Two New Species

Abstract

Two new chiggers from the intranasal passages of cricetid rodents from Joshua Tree National Monument, California are Microtrombicula nasalis sp. n. off Peromyscus eremicus, Peromyscus crinitus, Peromyscus truei, and Neotoma lepida; and Microtrombicula wrenni sp. n. off Peromyscus eremicus and Peromyscus crinitus. These species are closely related to Microtrombicula ornata (Loomis and Lipovsky) and Microtrombicula merrihewi (Loomis and Lipovsky) from the central United States. The presence of chiggers in the nasal passages of vertebrates was reported initially by Fain and Vercammen-Grandjean in 1953 from mammals of Africa. More recently Audy and Nadchatram (1957) described intranasal chiggers from rats in Malaysia; Southcott (1957) announced the discovery of a new chigger from the respiratory passages of a Pacific sea snake, and Yunker and Jones (1961) described two new genera of intranasal chiggers from bats of Panama. The latter were the first to be reported from the order Chiroptera and from the New World. The above reports prompted examination of the nasal passages of small mammals, which resulted in the discovery of two species of intranasal chiggers in mice and rats (family Cricetidae) of California. These chiggers were found in the anterior portion of the nasal passages of four species of cricetid rodents: Neotoma lepida Thomas, Desert Wood Rat; Peromyscus crinitus (Merriam), Canyon Mouse; Peromyscus eremicus (Baird), Cactus Mouse; and Peromyscus truei (Shufeldt), Pifion Mouse-trapped in late December 1961 and early February 1962 in Joshua Tree National Monument, California. The total number of larvae of both species per host varied from 1 to 8 (avg. 3.5 larvae), except for a single Cactus Mouse infested with 93 larvae. This mouse contained both species of chiggers, including more than 60 fully engorged larvae in the nasal passages. The presence of unengorged larvae in this mouse seems to indicate that February is a period of activity of the free-living larvae. S udies of these chiggers revealed that they represent two new species which seem to belong in the genus Microtrombicula Ewing, as redefined by Vercammen-Grandjean (1960). They are closely related to Microtrombicula ornata (Loomis and Lipovsky) and Microtrombicula errihewi (Loomis and Lipovsky) originally placed in the genus Trombicula and later in the ornata group (Loomis, 1956: 1324). T e species M. merrihewi was obtained from bats in Oklahoma and M. ornata from cricetid rodents taken in Kansas and Colorado. They were reported as being found in the ears of their hosts. From available information on the r recovery, these chiggers seem to have been obtained from detergent water placed under the living host and from washing the dead mammals. They were not taken directly f om the ears. In light of the discovery of these new, closely related species in the nasal passages, it seems probable that Microtrombicula ornata and M. merrihewi are also intra-