abstract A collection of laelapine mites from small mammals in the Galapagos Islands are identified and their host distributions reviewed. Two species of native rodents, Aegialomys galapagoensis and Nesoryzomys narboroughii , were infested only with laelapine species typical of Neotropical oryzomyine rodents; Rattus rattus was infested with Laelaps nuttalli , a host-specific ectoparasite endemic to Old World Rattus. A synopsis of Gigantolaelaps Fonseca is provided and we describe a new laelapine mite, Gigantolaelaps aegialomys n. sp., from the pelage of the rodent A. galapagoensis on Santa Fe Island. The new species has strong morphological affinities with a subgroup of Gigantolaelaps associated with a group of semiaquatic oryzomyine rodents ( Holochilus , Nectomys , Sooretamys , Pseudoryzomys , Oryzomys palustris ). The other nominal species of this group, Gigantolaelaps mattogrossensis (Fonseca, 1935) and Gigantolaelaps goyanensis Fonseca, 1939 , are characterized by 10 setae on Tibia IV, large metapodal shields, and spiniform setae on Coxae I. Gigantolaelaps aegialomys is distinguished from these species by a lack of clearly spiniform setae on Coxa I, with setiform distal seta longer than the proximal; metapodal shields about the same size as the stigma; less than 100 µm separating the first pair of sternal setae.

An intensive survey of ectoparasitic arthropods associated with small mammals in upland forests near Manaus, Brazil, provides information on the taxonomy and host distribution of laelapine mites in the Amazonian Region. We identified 5 genera and 21 species of these mites by comparison with representative museum specimens, the taxonomic literature, and, when possible, the original type specimens. These mites are host specific, with associations ranging from strict monoxeny (18 species) to oligoxeny (1 species) and pleioxeny (2 species). Marsupials were infested with species of Androlaelaps , echimyid rodents with Tur , and sigmodontine rodents with Gigantolaelaps , Laelaps , and Mysolaelaps . Androlaelaps bergalloi , a new species of Laelapinae, is described from the pelage of the marsupial Monodelphis brevicaudata .

Androlaelaps ilhacardosoi , a new species of Laelapinae, is described from the pelage of a 3-lined marsupial, Monodelphis americana , collected on Ilha Cardoso, São Paulo State, Brazil. The description is based on the female, and the systematics of laelapine mites associated with neotropical marsupials is discussed.

Mesostigmatic mites of the Laelapinae Berlese, 1892 (Acari: Laelapidae) are nidicolous arthropods that commonly occur in the fur of Neotropical small mammmals. In this 2-yr study, the laelapine acarofauna associated with the small mammal community in an area of Atlantic forest on Ilha Grande, Rio de Janeiro State, was examined, including observations on patterns of host specificity, mite dispersal, ecology, and food habits. A total of 1,347 laelapines was sampled from the pelage of 6 species of small mammals ( Marmosops incanus , Nectomys squamipes , Oryzomys russatus , Rhipidomys n. sp., Oxymycterus dasytrichus , and Trinomys dimidiatus ), all of which occurred exclusively in monoxenous associations with their hosts. No evidence of a blood meal was observed in the gut of the mites. With the exception of the 2 species of Tur , mite populations on hosts were entirely or nearly restricted to adult females. These results, together with some morphological characteristics of laelapines, reinforce the hypotheses that Neotropical laelapine mites are not ectoparasitic, and that females disperse by phoresy.