关键词: 小毛瓢虫属')">小毛瓢虫属, 瓢虫科')">瓢虫科, 12S rRNA, 16S rRNA, 28S rRNA, 系统发育')">系统发育

Abstract: 【Aim】 The genus Scymnus Kugelann is one of the most economically significant genera of natural enemy insects due to its predatory activity against pests including scale insects and aphids. However, the classification of this genus is still ambiguous, and the relationship of the subgenera within this genus is still in dispute. In order to establish a reasonable classification system of the genus Scymnus, the phylogenetic analysis is needed to further refine the taxonomic status of the subgenera within this genus. 【Methods】 The partial sequences of 12S, 16S and 28S rRNA genes from 44 species belonging to five subgenera within the genus Scymnus preserved in the Collection of South China Agricultural University were amplified using PCR. The inter-species genetic distance among the Scymnus species was calculated based on Kimura-2-parameter model using MEGA 7.0. The base composition of 12S rRNA, 16S rRNA and 28S rRNA genes was analyzed by using MEGA 7.0. The phylogeny trees were generated by maximum-likelihood (ML) and Bayesian-inference (BI) methods. 【Results】 The mean length of the 12S, 16S and 28S rRNA gene sequences amplified from the 44 species of Scymnus are 356, 351 and 315 bp, respectively. The average contents of A, T, G and C of 12S rRNA gene sequence are 38.8%, 43.5%, 11.9% and 5.8%, respectively, those of 16S rRNA gene sequence are 37.6%, 403%, 14.4%, and 7.7%, respectively, and those of 28S rRNA gene sequence are 26.7%, 18.3%, 31.4% and 23.5%, respectively. The inter-species genetic distance is 0.004-0.276 based on the concatenated sequence data, and the average genetic distance is 0.115. The phylogenetic analysis revealed that the genus Scymnus is monophyletic, while the subgenera Scymnus (Scymnus) Kugelann, Scymnus (Neopullus) Sasaji, Scymnus (Pullus) Mulsant and Scymnus (Parapullus) Yang are paraphyletic. 【Conclusion】 The phylogenetic analysis of Scymnus based on 12S, 16S and 28S rRNA gene sequences illustrated that the molecular classification system of this genus is not consistent well with its morphological classification system. In order to establish a reasonable classification system, other valid morphological characteristics should be explored to distinguish the relationships among the subgenera. Moreover, more research is needed to further refine the taxonomic status of the subgenera.

Key words: Scymnus, Coccinellidae, 12S rRNA, 16S rRNA, 28S rRNA, phylogeny