Embryonic Development Of The Larval Appendages Of Arge Pagana Panzer(Hymenoptera: Argidae)with Notes On Its Immature Morphology And Biology

Most larvae of Mecoptera,Lepidoptera and Hymenoptera Symphyta are eruciform,and are characterized by bearing abdominal prolegs besides three pairs of thoracic legs.However,the origin and homology of these prolegs are still controversial.In this study,we studied the embryonic development of the larval appendages and larval morphology of Arge pagana(Panzer,1798).Based on the embryonic features and larval morphology,we analyzed the origin of the prolegs of Argidae and the homology relationship between the prolegs of different eruciform larvae,and discussed whether the mandible is serially homologous with the maxilla.We also investigated all the immature stages of A.pagana,including the egg,larva,prepupa,and pupa,using light and scanning electron microscopy in order to provide knowledge on the recognition of the immature stages of this species.We examined the embryonic features of the mandible and maxilla of A.pagana to investigate the serial homology relationship between the mandible and the maxilla.At 90 h,the mandibles are just two unsegmented,subglobose processes.But the base of the mandible becomes 2-segmented at 105 h.At the same time,the molar lobe and incisor lobe appear.Based on our observation,the two segments on the base of the mandible correspond to the cardo and stipe of the maxilla,respectively;the incisor lobe and molar lobe correspond to the galea and lacinia of the maxilla,respectively.During the embryonic development of the mandible,we failed to find the structure which corresponds to the maxillary palp.So we think the mandible of A.pagana originates from the coxopodite of an appendage.Based on the morphology and embryology,we found paired medial swellings(proleg primordia)on the embryonic abdomen are not aligned with the thoracic legs and closer to the midventral line.During the embryonic development of A.pagana,the thoracic leg primordia are differentiated into six segments,while the proleg primordia are unsegmented and eventually develop into conical prolegs.Therefore,we conclude that the larval prolegs and thoracic legs of A.pagana are not serially homologous and the prolegs are derived from coxal endites of the abdominal appendages.During biological observation and artificial rearing,we found the egg of A.pagana is partly inserted into the tissue of twigs of Rosa chinensis(Jacq.).Under the scanning electron microscopy,the chorion in the plant tissue is furnished with irregular polygonal network and aeropyles,but the exposed portion of chorion is glabrous and aporous.Ten to twelve micropyles were on the posterior pole of eggs.The eruciform larva bears five pairs of ventral prolegs on abdominal segments II?VI and a pair of anal prolegs on segment X.A pair of prominent stemmata is present on the lateral side of head dorsal to the 1-segmented antennae.Male larvae have five instars,and female larvae have six instars.When fully-grown,the larvae move to the ground and spin cocoons to pupate inside.The pupae are yellow,exarate,taking the shape of the adults.This species completes about four generations per year,overwintering as prepupae in cocoons.The durations of egg,larva,prepupa,and pupa are 10?15,19?24,8?12,and 3?5 days,respectively.