Community Diversity And DNA Barcoding Of Alfalfa Insects In Loess Plateau Of East Gansu Province

Alfalfa(Medicago sativa) is one of the most widely grown leguminous forage in Northern China. Insect pests are one of the most important factors that limit alfalfa’s yield and quality. Rotation is a traditional crop cultivation pattern in rainfed agricultural region in Loess Plateau of east Gansu Province, and is an effective method for control of insect pests. During 2013-2015, insect community in Field Station of Lanzhou University(Xifeng District, Qingyang City, Gansu Province) was investigated, all collected specimen were identified, species diversity and dynamics of pests and natural enemies were analyzed, and some insect specimen were identified by DNA barcoding technique. The main results are as follows:1. All collected specimens are identified as 103 species in 42 families belonging to eight orders. Most specimens belong to three orders(Coleoptera, Lepidoptera and Hemiptera), with 80 species in 27 families. Most species are pests, accounting for over 80%, and mirids, true bugs, aphids and weevils are dominant groups. Ladybugs, lacewings and spiders are main enemy resources in the field station, and dominant species are Coccinella septempunctata, Harmonia axyridis, Adonia variegata, Chrysoperla sinica and spiders. The species and number of natural enemies in alfalfa field are higher that of crop field.2. Rotation and interplanting systems have control efficiency, but poor efficiency is observed in rotation patterns between crops from the same family. In contrast, rotations between forages and crops have good efficiency for pest control. Alfalfa field provides abundant food and good habitats for natural enemies which have a significant control efficiency for pests in neighbouring crop fields.3. A total of 146 insect specimens are PCR amplified and sequenced using mitochondrial cytochrome oxidase subunit I(COI) as molecular marker. The average K2 P genetic distance is 26.5%, and genetic distances within families are much lower that between families. Using ABGD and phylogenetic analysis, species identifications are performed for the three orders(Coleoptera, Lepidoptera and Hemiptera) which have the most high species diversity and are the most sequenced groups. The two methods have almost the same results. Species identification using the COI gene as barcoding marker is not always accurate at the order level, whereas reliable results are obtained at the family level.