Effects of spraying pesticide and grass management on arthropod community and relative stability in the apple orchard

Abstract：【Objective】In China, diseases and pests always occur in the apple- growing regions causing economic losses and restrict the development of apple industry. Conventional agriculture is based on a high level of chemical inputs such as pesticides and fertilizers, leading to serious environmental impacts, health concerns and loss of biodiversity in agrosystems. The reduction of pesticide use is a priority for intensively sprayed agricultural systems such as orchards. The preservation and promotion of biodiversity within orchards is therefore an issue to explore. The aim of this study was to determined arthropod community characteristics and relative stability of spraying pesticide and different grass managements in young apple orchards, to provide a reference for improving the effectiveness of ecological control in newly-built apple orchards.【Methods】We investigated the arthropod community in young apple orchards in Changli County, Qinhuangdao City in 2017, including six treatments, spraying pesticide clean tillage, ground cloth +inter-row natural grass, natural grass planting and no pesticide clean tillage, ground cloth + inter-row natural grass and natural grass planting. Arthropods were sampled at 15 day intervals from Mayto November, for a total of 11 sampling dates. Tree canopy survey and sweeping method were used in this study. Within each treatment, five similar heights apple trees were selected as sample to monitor the community of arthropods, sweeping surveys were used to catch ground-cover arthropod. Arthropod community were divided into parasitic community, predacious community, herbivore community and neutral community. The community characteristic index, community similarity, community relative stability, principal component analysis and cluster analysis were used in this study.【Results】The results showed that 206 168 arthropod were collected in young apple orchards, belonging to 14 orders, 77 families, and 123 species. The main phytophagous pests included Aphididae, Thripidae, Hoppers, the main predatory enemies were Argiopidae, and neutral species were Muscidae. Compared with no spraying management, the number of herbivorous pests in natural grass communities were significantly reduced after spraying of pesticides, but there was no significant difference on the number of herbivorous pests in clean tillage and ground cloth + row natural grass The number of predacious and parasitic natural enemies in natural grass and ground cloth + row natural grass were significantly decreased, and neutral community were diminished in clean tillage. Regardless of the spraying pesticide, the grass significantly increased the number of parasitic and predacious natural enemies and neutral individuals in the young apple orchard, but had no significant effect on the number of herbivorous pests. Compared with no spraying for the community characteristic indexes, the arthropod community diversity index (H’) and evenness index and (J) and richness (S) of clean tillage, natural grass and ground cloth + row natural grass treatment were significantly lower, whereas the community dominance index was higher. Under spraying, the index of S, H and J were significant higher in natural grass and ground cloth + row natural grass compared with clean tillage, whereas C was higher in clean tillage than the others. Under no spraying, the index of S and J were significant higher in natural grass and ground cloth + row natural grass compared with clean tillage, whereas C was higher in clean tillage than the others, and there was a significant difference in the index of H’. In all plots, the index of richness/number of total arthropod community (S/N) were greatly reduced, but no significant difference in the index of species number of predatory group/species number of herbivorous group (Sn/Sp). Under spraying, there was significant difference in the index of S/N, but no significant difference was observed in the index of Sn/Sp. Under no spraying, the index of S/N was significantly higher in natural grasses and ground cloth + natural grass than in clean tillage. No significant difference was observed in the index of Sn/Sp. Principal component analysis showed that species diversity index, evenness, species number, dominant concentration were the first principal component, species richness was the second principal component, and the five components all influenced the community composition. The results of similarity index and cluster analysis showed that the arthropod community was divided into four categories: natural grass spraying and ground cloth + inter-row natural grass spraying, natural grass spraying and inter-row natural grass spraying, clean tillage spraying, clean tillage without spraying.【Conclusion】Pesticide had an negative effect on arthropod community diversity index and stability after spraying pesticide. Moreover, natural grass bring a considerable improvement in arthropod pest management by enhancing the structure of community diversity, evenness, relative stability and quantity of natural enemies within the apple orchard systems. Therefore, our results indicate that natural grass in young apple orchards can optimize the arthropod community structure, increase community diversity, evenness, relative stability, and the number of natural enemies. It can gradually achieve the purpose of controlling harmful organisms through ecological pathways and reducing the use of chemical pesticides.