Morphogenesis of embryonic appendages of Arge pagana Panzer (Hymenoptera: Argidae)

Abstract

The larvae of hymenopteran Symphyta are eruciform, with several pairs of abdominal prolegs in addition to three pairs of thoracic legs. However, it is still controversial whether these abdominal prolegs are serially homologous with the thoracic legs. Here we studied the embryonic development of the larval appendages of the large rose sawfly Arge pagana (Panzer, 1798) to investigate the origin and homologous relationship of the abdominal prolegs of Argidae. The results show that paired swellings (proleg primordia) on the embryonic abdomen are not aligned with the thoracic legs, but are slightly closer to the midventral line. During the embryonic development, the thoracic leg primordia are differentiated into six segments, while the abdominal appendage primordia remain unsegmented and eventually develop into conical prolegs. The abdominal prolegs of larval A. pagana are likely developed from the endites of the primary embryonic appendages, and the paired anal prolegs arise from the eleventh abdominal segment. Therefore, the abdominal prolegs of sawfly larvae are very likely to have an appendicular nature but not the main axes of appendages.