| Pentatomidae is a big family of Hemiptera-Heteroptera. There are 760 genera 4100 species known in the world and about 170 genera 500 species known in China so far. All of them live on land. Most species of Pentatomidae are phytophagous insects.They are important pests of agriculture and forest. Asopinae are all predatory insects, and they are important natural enemy insets that can be used in biocontrol of pests. So insects of Pentatomidae are very important in economy. There have comprehensive studies of classification, cell biology, biochemistry, ecology, biocontrol and other aspects of Pentatomidae home and abroad. However, there are lots of debates about the phylogenetic relationships of subfamilies and genera in the systematics of Pentatomidae all the times. Former researchers have discussed it from the aspects of external morphological characters, eggs' characters, chromosome characters etc. But no consentaneous opinions have being obtained.In this paper, partial species of Pentatomidae are studied from morphology and molecular systematics. As for morphology, we selected 40 important external characters and constructed the phylogenetic relationships of some species of Pentatomidae by using parsimony method of Wagner. In molecular systematics studies, we amplified and sequenced mitochondrial cytochrome oxidase (COII) gene 585 bp sequence from 23 species of Pentatomidae (19 species), Scutelleridae (2 species), Tessaratomidae (1 species) and Cydnidae (1 species). Based on the analyses of COII gene sequences, we reconstructed the phylogenetic relationships of these species from family, subfamily and genus aspects by using Neighbor-Joining (NJ), Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI) methods.Summarizing the outcomes of two aspects, we can conclude the results as follows:1. The parsimony analysis based on 40 morphological characters of some species indicates that the relationship of 4 subfamilies is Phyllocephalinae + (Asopinae+ (Pentatominae+Podopinae)). Pentatominae has a close relationship with Podopinae, while Phyllocephalinae has a relatively far relationship with other subfamilies.2. The average content of A, T, G, C of COII gene sequences of 19 species of Pentatomidae are 39.8%, 31.8%, 12.5%, 15.8% respectively. And A+T content is 71.7 %, G+C content is 28.3 %, which shows a strong A+T bias. The COII gene sequence ofall insects coding 195 amino acids except Scotinophara Horvathi which only coding 190 amino acids. Average variation rate of amino acids is 40.5%. All insects contain 19 kinds of amino acids, not contain Cys. The content of Leu and He are very high.3. The average transition and transversion ratio of COII gene sequence is 0.9. Transversion is just a little higher than transition. Sequence substitution saturation analysis indicates that the substitution is not saturated. Most transition occurs between T and C, and most transversion occurs between A and T.4. Genetic distances show that the distance among the species of the same genus is the smallest. For example, the distance between Carbula obtusangula and C. sinica is 0.082, the distance between Eurydema dominulus and E. gebleri is 0.063. Distances among the genera of Pentatominae ranged from 0.132 to 0.190, bigger than distances among species of the same genus. Distances among subfamilies ranged from 0.143 to 0.204. The distance between ingroup and outgroup is the biggest one (0.193-0.240).5. Downloading the COII gene sequence of Oncopeltus fasciatus from GenBank database as a outgroup, we reconstructed the phylogenetic relationships of Pentatomidae, Scutelleridae, Tessaratomidae and Cydnidae. The result supports the categories of every family, insects of Pentatomidae clustered together. Tessaratomidae clustered with Cydnidae, seemingly more primitive than Scutelleridae, which contradicted with the conclusion of morphology that deems Scutelleridae and Tessaratomidae as a sister group. Molecular data can not resolve all relationships between these 4 families. Long branches are attracted together probably caused by the small size of samples, which also attributed to the relatively quick evolution rate of COII gene.6. When select 2 species of Scutelleridae as outgroup to construct the phylogenetic relationship of all 19 species of Pentatomidae, trees contructed by different methods indicate that Phyllocephalinae is more primitive. However, all trees can not resolve the relationship of other 3 subfamilies. This problem might be caused by the bias of sampling. So we selected 2 genera from every subfamilies and reconstructed the relationships of four subfamilies. Relationships of 4 subfamilies are well resolved. The relationship derived from molecular data is: Phyllocephalinae+ (Pentatominae + (Asopinae+Podopinae)).7. Based on COII gene sequences, the relationships of 11 species of Pentatominae can be well resolved. There are 3 branches can be observed: Pentatoma, Eurydema+Plautia, Carbula+Halyomorph. The results support the conventional...
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