Embryogenesis of the fairy moth, nemophora albiantennella issiki (Lepidoptera, Adelidae), with special emphasis on its phylogenetic implications

Early embryogenesis and features of the developing embryo of the fair moth, Nemophora albiantennella (Lepidoptera : Adelidae), were studied chiefly by light microscopy for evaluating the systematic position of the family Adelidae, and the phylogeny of the heteroneuran Lepidoptera from the comparative embryological standpoint has been discussed. The newly laid egg of this species is elongated ovoid, about 0.53×0.22 mm in size; the size rapidly increases to about 0.62×0.34 mm in 1–3 days after oviposition probably owing to absorption of water. The egg period is about 7 days at 20°C, and is divided into 12 developmental stages. Possible embryonic synapomorphies shared by the Adelidae (Incurvarioidea), Nepticulidae (Nepticuloidea), and Ditrysia are as follows; formation of a large germ disk, the serosa and amnion formed independently in the fault type, the embryo immersed in the yolk before revolution, and the absence of the 11th abdominal segment. The Nepticuloidea is linked to the Ditrysia by two synapomorphies; the embryo immersed in the yolk until just before hatching, thickened serosal cells (hydropyle cells) absent. The only apomorphic embryonic characters observed in the Ditrysia are the thick periplasm and constancy of egg volume. The phylogeny obtained from the distribution of these embryonic characters is : Incurvarioidea+(Nepticuloidea+Ditrysia). Although this relationship strongly supports the monophyly of the infraordinal taxon Heteroneura, it does not coincide with any other arrangements formerly proposed on the basis of adult and larval characters.