关键词: 半翅目, 头喙亚目, 形态, 发育, 同源性, 共生菌

Abstract: 【Aim】 This study aims to clarify the embryonic development process of the cicada Cryptotympana atrata and the distribution of symbionts in the embryo, determine the number of instars of nymphs, and clarify the morphogenetic process of related organs and the correlation between the morphological changes (differentiation) of nymphs and the habitat as well as the nutrient supply conditions of host plants. 【Methods】 By field collecting and laboratory artificial breeding, samples of various developmental stages of C. atrata were obtained, and the embryonic development was observed and the morphological changes of nymphs at different instars were measured and analyzed using optical microscopy and electron microscopy. 【Results】 The eggs of C. atrata are elongated with reticulated stripes on the chorion, and the micropyle is located about a quarter the distance of the egg length from the posterior pole. At the early stage of embryonic development, the symbiont Candidatus Sulcia muelleri (Sulcia) and the yeast-like fungal symbionts (YLS) gathered to form a “symbiont ball” near the posterior pole of the egg. At ~72 h after oviposition, the newly formed germ band gradually merged into the yolk, and the symbiont ball gradually moved to the anterior pole and finally entered the nearby host cells, which finally colonized the dorsal region of the 6th-8th abdominal segments. At ~55 d after oviposition, the embryo entered diapause for overwintering, and the diapause period was about 130 d. During the early stage of embryonic development, the labral appendages gradually fused basally, and eventually fused with the anteclypeus. The appendages of the mandible segment extended continuously, and modified to form the mandibular stylets. The maxillary appendages differentiated into the lateral and medial prominences, which further developed into the proximal maxillary plate (eventually disappeared) and the distal maxillary stylet, respectively. The labial appendages appeared in pairs at the early stage of embryonic development, but gradually fused to form the rostrum to contain the mandibular and maxillary stylets. At ~200 d after oviposition, the pleuropodium formed at the first abdominal segment, which gradually degenerated by the time of dorsal closure at ~210 d after oviposition. The pronymph had no tooth on the head but possessed massive tooth-bulge on the thorax and abdomen, which could help the insect to crawl out from the egg shell. At ~245 d after oviposition, some of the embryos began to hatch. The nymphs had five instars, which exhibited a series of morphological changes in the compound eyes, antennae, wing buds, thoracic legs and reproductive segments, along with the increase in body size. Particularly, the three pairs of thoracic legs showed significantly morphological/functional differentiation during the nymphal stage: the mesothoracic and metathoracic legs were slender and suitable for supporting and balancing the body; the prothoracic legs were thick and strong, with femoral comb gradually developed on the flattened femur, and an apical tooth and a blade formed on the sickle-like tibia, which are suitable for digging tunnels and fixing the body on the root of host plants for feeding. The 1st-4th instar nymphs morphologically differentiated into two types: individuals of Type Ⅰpossessed a swollen abdomen, and individuals of Type Ⅱ possessed an unswollen abdomen. In contrast, the 5th instar nymphs showed no obviously morphological differentiation. In addition, the differentiation of the 1st instar nymphs feeding on vigorous host plants appeared earlier than those feeding on weak host plants; the 1st instar nymphs with an unswollen abdomen entered the 2nd instar earlier than those with a swollen abdomen; and all the nymphs initially entered the 2nd instar with an unswollen abdomen. 【Conclusion】 During the embryonic development process of C. atrata, the symbiont ball consisting of Sulcia and YLS migrates from the posterior pole to the anterior pole of the egg, and finally colonizes the 6th-8th abdominal segments. The mandiblular stylets are coxognathic and the maxillary stylets telognathic in origin. The nymphs of C. atrata have five instars, and the morphological/functional specialization of the nymphs are closely associated with the very long, subterranean pre-adult stage and the niche shift between the nymphal and the adult stages, as well as the nutrient supply of the host plants.

Key words:  Hemiptera; Auchenorrhyncha, morphology, development, homology, symbionts