Embryonic Development Of Subpsaltria Yangi Chen And Morphology And Structure Of Compound Eyes Of Last-instar Nymphs And Adults Of Meimuna Mongolica(Hemiptera:Cicadidae)

The embryonic development of insects can provide important information for taxonomy and phylogenetic analysis of related taxa.Compound eyes are important visual organs of insects,which also have important significance in phylogeny.In this study,the embryonic development of Subpsaltria yangi and the morphology and structure of the compound eyes of nymphs and adults of Meimuna mongolica were observed using light,scanning and transmission electron microscopy.Results and conclusions are as follows:1.The embryonic development of S.yangi undergoes about 34 days,which can be divided into seven stages according to the external embryonic features.The labial and labral appendages exist as a pair of independent processes during the first 13 days(Stages 1–3),but begin to fuse with each other in the midline since then(about 337 h)(Stage 4),and become completely fused at the 15 th day(about 350 h later after oviposition)(Stage 5).The appendages of thorax have differentiated in Stage 2(152–174 h).The abdomen comprises five segments in the early embryonic stages(Stages 1–2),but consists of 11 segments in the late embryonic stage(408–816 h)(Stage 7),which is the same as that in the first-instar nymphs and less than that in the adults(abdomen of adults comprises nine segments),suggesting the abdominal segments fused or degenerated during the development of the elder nymphs.The mandibular and maxillary stylets of an embryo are short and tubular-like during the late embryonic development,with more basal parts keep developing inside the head capsule.The antennae of the first-instar nymphs comprise the scape,pedicel and the flagellum,and the flagellum is composed of five subsegments.The thoracic legs of the first-instar nymphs all consist of coxa,trochanter,femur,tibia,tarsus and pretarsus.The pretarsus of all legs are well developed,with a pair of claws.The forelegs of the first-instar nymphs have developed into digging legs,in which a groove is present on the ventral side of the femur,and posterior tooth and accessory teeth are embedded in the groove.The results of this study may inform future studies on the embryonic development and control of cicadas,and provide information for phylogenetic analysis of hemipteran insects.2.The compound eyes are of apposition type,and the color of the compound eyes of the last-instar nymphs change from white into red and dark brown gradually before the adult emergence;whereas the compound eyes of the adults are light brown.Basiconica,trichoid and chaetica sensilla were observed on the surface of the compound eyes of nymphs,but no sensilla were found on that of adults.The white compound eyes of nymphs have a complete cornea,from which ommatidia could not be found.The red and dark brown compound eyes of nymphs are composed of many irregular,hexagonal or pentagonal ommatidia;whereas the compound eyes of adults are composed of equilateral hexagonal ommatidia.The white compound eyes of nymphs are composed of a large amount of clustered cells,and no ommatidia were observed.In each ommatidium of the dark brown compound eyes of nymphs,the nuclei of secondary pigment cells are distributed between the rhabdom and the crystalline cone.In the compound eyes of adults,the nuclei of secondary pigment cells are distributed around the proximal center of crystalline cone.In the dark brown compound eyes of nymphs,the pigment granules of the primary pigment cells and retinula cells are evenly distributed,while those in the compound eyes of adults are mainly distributed around the rhabdoms.The compound eyes of nymphs and adults of M.mongolica have significant differences in the development of ommatidia,the distribution of pigment cells,and in the presence or absence of sensilla.We conclude that the compound eyes of nymphal cicadas of young-instars and in the earlier development stage of the last-instar do not have visual ability,but can function to sense mechanical pressure or other environmental signals underground.This should be an adaptation to the niche shift during the ontogeny of cicadas which live underground for a very long time in the nymphal stage and have a short adult lifespan above ground.Findings of morphological,ultrastructural and functional characteristics of compound eyes of nymphs and adults of this species improve our understanding of the development and function of compound eyes in Cicadoidea,which are informative to future study to clarify the phylogenetic relationship between Cicadoidea and allies in Hemiptera.