Pretarsal structures in Reduviidae (Heteroptera, Insecta)

A survey of pretarsal structures in Reduviidae of 22 higher-level taxa and several outgroup representatives is conducted using scanning electron microscopy (SEM) and light microscopy. Based on histology and SEM, pretarsal structures are described in detail for Rhodnius prolixus. Structures of the distal tarsomer, which appear to be functionally correlated with the pretarsus, are documented for the first time in Heteroptera. These comprise lateral oval sclerites, two campaniform sensilla and two marginal setae, observed in Reduviidae and other heteropteran taxa. The presence of a peg-like dorsomedian sensillum medially between the claws in Reduviidae and Nabidae is demonstrated. As a result of its structure and position, homology of this sensillum with the 'dorsal arolium' in other heteropteran groups is proposed. Within Reduviidae, the transformation of the peg-like dorsomedian sensillum to a campaniform sensillum, as seen in most representatives of the harpactoroid complex, is hypothesized. The first record of parempodia other than setiform within Reduviidae is noted in nymphs of Harpactorinae, which may possess lamellate parempodia. Several characters that are possibly useful for clarifying relationships among the harpactoroid groups are described and discussed. The pretarsal structures, including the unguitractor plate and the tarsal marginal setae among reduviid groups are discussed in a phylogenetic context.