Observations on the Subgenus Argas (Ixodoidea: Argasidae: Argas). 18. Haller's Organ Roof and Anterior Pit Setae

Abstract

Adults of 18 of the 22 spp. constituting the subgenus Argas, which parasitize birds nesting and resting in rocky habitats in each faunal region of the world (15 spp.) or in trees (3 spp.) (2 Neotropical, 1 Nearctic), were studied by SEM [scanning electron microscopy]. In each except 3 Neotropical species, the 9 setae of the anterior pit of tarsus I are arranged in an anterior group (1 serrate, 1 setiform, 1 conical) and a posterior group (2 fine, 2 porose, 2 grooved), or the 2 groups are more or less confluent. Abnormally additional setae may occur on 1 or both tarsi of a single specimen. In 1 Neotropical species, only the 3 anterior group setae are present. In 3 Neotropical species, only these 3 setae and a 4th seta are present (whether 6 or 5 additional setae are concealed within the tarsal structure should be investigated). The Haller''s organ capsule is entirely open (unroofed) (3 spp.), roofed posteriorly and open anteriorly (7 spp.), or mostly roofed by a plate which is pierced by 1 large aperture and by more or less numerous, small, or medium-sized perforations (8 spp. plus one other not studied). The structure of Haller''s organ probably evolved in different lines in response to a multiplicity of biological factors related to the behavior and habitat of individual species.