Endoparasitic Chiggers: VIII. The Intradermal Genus Intercutestrix Brennan and Yunker, 1966, and Three New Species (Acarina: Trombiculidae)

Abstract

Intercutestrix is redescribed, and the new species I. exigua off Proechimys semispinosus and Sigmodon hispidus, Venezuela, I. incomitata off Hoplomys gymnurus, Colombia, and I. pisinna off Proechimys guyannensis, Venezuela, are described. A key to the 5 included species is given. Three new species of the Neotropical intradermal genus Intercutestrix have prompted a generic redescription and assay of promising structural features for ready identification of the minute larvae. Contributing to this study are two species (I. exigua and I. pisinna) collected in Venezuela under the supervision of Dr. Charles 0. Handley, Smithsonian Institution, and Dr. Vernon J. Tipton, Brigham Young University, and one species (I. incomitata) collected in Colombia by Mr. Kjell von Sneidem under the direction of the Field Museum of Natural History. Intercutestrix Brennan and Yunker Intercutestrix Brennan and Yunker, 1966, p. 237. Neotropical trombiculine larvae, intradermal parasites of small mammals, principally rodents of the family Echimyidae. Broad ellipsoidal to subcircular when engorged. Scutum arcuate, considerably wider than long, with shallow sinuous margins. Five scutal setae, anteroand posterolaterals approximate, the latter far anterior to the sensillary bases. Sensillae caducous, known only in one specimen of I. mondolfii where they are broad obovate and moderately setulose. Eyes minute, 2/2 in an indistinct plate, the posterior pair sometimes evanescent. Cheliceral blade small with tricuspid cap. Galeal seta nude. Palpal tibial claw slender, trifurcate; palpal tarsus with 4 branched setae and a tarsala. Leg segmentation 7-6-6; legs with 2 genualae I, no genuala II and III, a tibiala Received for publication 2 July 1973. * This work was supported in part by Department of the Army Contract DA-49-193-MD-2788 with the Smithsonian Institution (Ecology and distribution of mammalian ectoparasites, arboviruses, and their hosts in Venezuela). t U. S. Department of Health, Education, and Welfare, Public Health Service, NIH, NIAID, Rocky Mountain Laboratory, Hamilton, Montana 59840. $ Department of Zoology, Brigham Young University, Provo, Utah 84601. III, no mastisetae, a suband abbreviate parasubterminala, microtarsala I lateroproximad of tarsala I; coxae unisetose. Type species: Euschongastia tryssa Brennan and Jones, 1961. Referred species: Intercutestrix mondolfii Brennan and Yunker, 1969, I. exiguia sp. n., I. incomitata sp. n., and I. pisinna sp. n. Species of Intercutestrix seem to prefer rodent hosts of the family Echimyidae, particularly of the genus Proechimys, although they have been recorded from other rodents and opossums. The minute larvae are rather elusive because of their intradermal habitat where they occur singly, almost completely enclosed in a keratinous cyst, and are found ventrally on the host only by thorough and specific examination (Brennan and Yunker, 1969). Consequently, samples resulting from general chigger collecting are most often small and inadequate for precise and conclusive taxonomic study. Disregarding other structural characters, the five included species are separable by form, size, and arrangement of dorsal setae. The scutum, in the almost invariable absence of sensillae, and setation of the appendages are not remarkable, and offer little aid in specific identification. Figures of scutum and specialized setae of legs were given by Brennan and Jones (1961) for I. tryssa and by Brennan and Yunker (1969) for it and I. mondolfii. Thus, an illustration of scutum and specialized leg setae for only one new species, I. exigua, will suffice here. Key to larvae of Intercutestrix 1. Second posthumeral row with 10 setae (Peru) -.-. --------.-.......tryssa Second posthumeral row with 6 setae .---2 2. Palpal setal formula B/B/BBB, dorsal setal formula begins 2-10 (Colombia) ----)-----...--...... -. .......incomitata