Structure And Dynamics Of Alfalfa Arthropod Communities In HeXi Region

The arthropod community of alfalfa fields was investigated for two consecutive years from2021 to 2022 in Zhangye,Gansu.We clarified the community composition and distribution characteristics of arthropods in alfalfa fields by using population ecology and geostatistics,mapped the community characteristics and dynamic changes of major pests and natural enemies in alfalfa fields,explored the effects of different management modes on the structure and stability of arthropod communities in alfalfa fields.And clarified the spatial and temporal dynamics of aphids and ladybugs in alfalfa fields,providing a scientific basis for the integrated management of pests and the conservation and utilization of natural enemies in alfalfa fields for the Hexi region.The main findings are as follows:(1)The arthropod community of alfalfa fields in Zhangye area was rich in species.A total of 39 species in 8 orders and 22 families were surveyed in two years,including 24 phytophagous pests in 6 orders and 15 families,14 predatory natural enemies in 5 orders and 6 families,and1 parasitic natural enemy.Aphidinae,Thripidae,Lygus pratensis Linnaeus,Propylea japonica,Araneida,Orius similis are the dominant arthropod populations in alfalfa fields.The phytophagous subcommunity was the main component of the total arthropod community,and was much higher than that of the predatory subcommunity in relative abundance.The dominant phytophagous pest species were Aphididae and Thripidae,and the dominant natural enemies were Coccinellidae,Anthocoridae and Arachnida Araneida.(2)The temporal dynamics of the total arthropod community and subcommunity structure of alfalfa fields in Zhangye showed regular changes.The first maximum population of arthropods in 2022 was reached around May 26,with a sharply increasing population of arthropod communities on regenerating alfalfa,with a 2nd peak in early July in each plot,and a decreasing population of arthropods as the alfalfa matured.During 2-year investigation,the changes in the phytophagous subcommunity over time were consistent with the trends in the total arthropod community.Mowing significantly reduced the population number of arthropods,and with the regeneration of alfalfa,the populations of phytophagous pests as well as predatory natural enemies recovered gradually.(3)Mowing had a significant effect on arthropod diversity in alfalfa fields.By investigating the arthropod in mowing and non-mowing alfalfa fields,we found that mowing could significantly reduce the arthropod populations as well as species numbers in alfalfa fields,but had little effects on natural enemies.Using the level of community characteristic parameters as the indicators,our study indicated that the level of arthropod diversity in the non-mowed field was significantly higher than that of mowed field.Altogether,our study showed that mowing could enhance the evenness of arthropod communities by weakening the dominant species of the community,and balancing the species and number of pests and natural enemies to make the community more stable.(4)P.japonica had an appreciable time-spatial following performance to alfalfa aphids.We ranked the natural enemies of aphids and ladybugs according to affinity index in quantity,time and space,the P.japonica was the dominant natural enemy of aphids.The population dynamics results showed that the population occurrence trends of P.japonica and aphids were similar,with an obviously significant following effect.The traditional statistical analysis showed that the distribution pattern of aphids was uniform throughout the alfalfa reproductive period;P.japonica was uniform,aggregate,uniform and uniform distributed during the budding-early flowering,blooming,podding and maturity periods,respectively;while ladybugs larvae were aggregate,aggregate,uniform and aggregate distribution.The geostatistical analysis showed that the best-fitting models for aphids,P.japonica and ladybug larvae in the budding-early flowering stage were exponential,exponential and linear;the blooming was linear,spherical and linear;exponential,exponential and linear at podding;mature periods were spherical,linear and linear,and all spatial distribution types were aggregated.A simulated map of the 3D and 2D spatial distribution obtained by Kriging interpolation,with the center of aggregation of aphids at the budding-early flowering stage in the southwest;the concentration centers of the ladybug species were in the southeast.From the blooming to maturity,P.japonica and ladybugs larvae overlapped with the aphid aggregation center.The ranking of the angular cosine coefficients between the natural enemies of the 3 types of ladybugs and the aphid population variation was carried out,and the P.japonica’s was the largest,showed that P.japonica was the dominant natural enemy of the aphids in alfalfa fields in the Hexi region,and had a more effective following effect on the aphid population.