Comparative Morphology And Ecology Of The Nymphs Of The Dominant Cicadas In Guanzhong Plain, Shaanxi Province, China(Insecta: Hemiptera)

The cicadas Cryptotympana atrata(Fabricius), Meimuna mongolica(Distant) and Platypleura kaempferi(Fabricius) are the three dominant species of the Cicadidae in Guanzhong Plain, Shaanxi Province, China. Previous studies on these cicadas were mainly focused on adult morphology and taxonomy, whereas studies about their nymphs are limited. This study is mainly focused on morphology and ecology of the nymphs of these three species.The present investigation provides comparative morphometrics of the final instar nymphs of these three dominant species. Particularly, characters on the antennae, legs, and apex of abdomen of both males and females of these three species were investigated and analyzed. In addition, the numbers of hind tibial spines of the final instar nymphs of 21 representatives of Cicadoidea were compared. The results provide useful characteristics for nymph identification of related species and for further taxonomic and phylogenetic analysis of Cicadoidea.This study investigated the morphometrics of different instar nymphs of M. mongolica. Particularly, characters on head capsule width and abdominal width were investigated and analyzed. The first-instar nymphs of M. mongolica hatched from eggs and others excavated from the soil of three main host plants(Pinus tabuliformis Carr., Populus tomentosa Carr. and Pyrus xerophila Yü). The mitochondrial COI barcode was employed to further ensure that all individuals(including the variants) belong to M. mongolica. Five instars of nymphal M. mongolica were determined using Dyar’s rule and a regression analysis of the head width of nymphs. Nymphal instars, morphological variation, vertical distribution and population density in soil, and emergence phenology of nymphs of M. mongolica on these three host plants were also studied. To investigate the adult emergence phenology and sex ratio of M. mongolica, exuviae were collected regularly. Results show that(1) the mean densities of nymphs in soil under the three host plants were notably different, i.e., 3.50 nymphs/m2, 12.67 nymphs/m2 and 26.5 nymphs/m2 under P. tabuliformis, Po. tomentosa and Py. xerophila, respectively.(2) The nymphs could extend their distribution from the 0–10 cm soil layer to the 51–60 cm soil layer underground, but not beyond 60 cm soil layer under all the three host plants.(3) Nymphs of third- and fourth-instars present morphological variation. Two types were observed according to the widths of abdomen, e.g., swollen abdomen(Type I) and un-swollen abdomen(Type II). The mean widths of abdomen of the third-instar nymphs of the two types were highly significant, i.e., 3.44±0.14 mm(Type I) and 1.80±0.04 mm(Type II), respectively. The mean widths of abdomen of the fourth-instar nymphs of the two types were also highly significant, i.e., 6.03±0.14 mm(Type I) and 3.29±0.16 mm(Type II). The morphological variation is generally related to host-plant association. Abdomens of nymphs feeding on Po. tomentosa were usually swollen(Type I) with body color mainly white or greenish white; abdomens of nymphs feeding on Py. xerophila were usually swollen(Type I) with body color mainly white; abdomen of nymphs feeding on P. tabuliformis were either swollen(Type I) or un-swollen(Type II), and the former with body color mainly white, and the latter mainly pale brown.(4) Emergence of M. mongolica got started in mid-July and ended in late August, and a protandrous emergence pattern was evident. The sex ratio of the entire population was nearly 1:1, but males dominated in the early 17-d duration the emergence.Population dynamics and the rate of malformed cicada nymphs of the three cicadas in normal habitat and the contaminated habitat by construction and demolition(C&D) waste were investigated in July 2011、2013 and 2014. Results show that(1) in normal habitat, the rate of malformed cicada nymphs is about 3.45%, and there are no significant differences between host plants and years, whereas in contaminated habitat, the rate of malformed cicada nymphs gradually rises year by year, with highly significant differences among the three years.(2) The cicada M. mongolica may evolve into the only one dominant species, gradually replacing the other two species when compete with them in the same ecological niche. There is a distinct trend of decline of the population density of younger and final instar nymphs of C. atrata under the host plant Po. tomentosa in the three years; and a distinct trend of decline of the population density of younger and final instar nymphs of P. kaempferi was also found under the host plant P. tabuliformis in the three years. Conversely, there is a trend of slow increase of the population density of younger and final instar nymphs of M. mongolica under the three main host plants in the three years. These findings suggest that cicada nymphs may be good candidates to act as bioindicators of soil pollution by C&D waste.