Morphology of the pretarsus of the sawflies and horntails (Hymenoptera: 'Symphyta').

The pretarsal structures have been studied in representatives of 13 families of 'Symphyta' by means of light microscopy. The pretarsal sclerites (manubrium, planta, and unguitractor) vary in shape among different families. The shape of the manubrium is triangular in representatives of Xyelidae and Orussidae and bifurcated in those of Tenthredinoidea. For representatives of Siricomorpha, an elongated shape of the manubrium is typical with such variations, as distally expanded, proximally expanded, clavate, spear-shaped. Plantae of different Symphyta vary in shape and level of sclerotization. In representatives of Siricidae, the female manubrium and arolium are significantly reduced, and arcus and dorsal plates are completely absent. Siricid males possess all pretarsal sclerites and a well-developed arolium. Auxiliary sclerites are absent in representatives of Orussidae. Trichoid sensilla are absent on the plantae in representatives of Cephidae and Orussidae. Other studied Symphyta possess two trichoid sensilla on the planta. Representatives of all investigated families bear two campaniform sensilla on the manubrium, with the exception of Siricidae having three sensilla. Kinematics of the pretarsus with bifurcated manubrium are modeled and discussed.