Comparative morphology of the Pentatomoidea pretarsus (Hemiptera: Heteroptera)

Heteropteran legs are very diverse within and among taxa, and such variation is frequently correlated with life habits. Structural modifications are commonly present in the legs of the Pentatomoidea but are poorly studied. Using scanning electron microscopy, the pretarsal microstructure of species representing all families of the Pentatomoidea (i.e., Acanthosomatidae, Canopidae, Cydnidae, Dinidoridae, Lestoniidae, Parastrachiidae, Pentatomidae, Phloeidae, Plataspididae, Scutelleridae, Tessaratomidae, Thaumastellidae, and Urostylididae) was described. The generalized pentatomoid pretarsus comprise paired claws, pulvilli, and parempodial sclerites with paired parempodial setae, a median sclerite, and the unguitractor plate, all of which are connected to one another by membranous areas. Variation can be found in the claws, pulvilli and parempodia. The claws are usually smooth in pentatomoids, but the claws of Urostylididae and Acanthosomatidae bear setae at the outer surface. The pulvilli, large and robust, are divided into basi- and distipulvilli.  Pulvilli that are long and narrow, usually flattened, and undivided into basi- and distipulvilli are found on some Cydnini and Geotomini (Cydnidae), on the Phloeidae, and on the Phyllocephalinae (Pentatomidae); while the absence of pulvillar structures has been documented only for Scaptocoris minor (Cydnidae). The parempodial projections are variable in the pentatomoid families, whereas in the Thyreocoridae they are elongate with an acute apex. The taxonomic and phylogenetic relevance of pretarsal traits are discussed on the light of the current Pentatomoidea phylogenetic hypothesis.