Impacts of field margins and organic practices on arthropod natural enemy and pest diversities in paddy fields

Although the expansion of agricultural land and intensive production have contributed to increased food production, the resulting high-intensity human disturbances and excessive use of agrochemicals have caused significant environmental damage. This has led to the loss of biodiversity and degradation of ecosystem services, ultimately posing threats to both sustainable food production and human health. Therefore, it is crucial to develop sustainable production management strategies. Organic production at the field scale and the establishment of flowering boundaries are considered efficient measures for biodiversity and ecosystem services. However, few studies have investigated whether organic practices and flowering boundaries can effectively increase the natural enemies of arthropods and improve the control of pests in cultivated fields, particularly in paddy planting systems. In this study, we aimed to fill this knowledge gap by investigating the distribution and diversity of natural enemies and pests of arthropods in paddy fields and their field margins, and how vegetation on the field margin affect diversities of natural enemies and pests of arthropods in paddy fields. The following three treatments were established: conventional paddy fields with traditional field margins (Con), organic paddy fields with traditional field margins (Org), and organic paddy fields with flowering boundaries (OrgF). Arthropods were sampled at the field margins and in paddy fields 5 and 20 m away from the margin using a suction sampler. Vegetation coverage and diversity in the field margins were also investigated. The results are as follows: 1) a total of 9531 arthropods belonging to 50 families were caught, with 2653 individuals identified as natural enemies from 28 families (including 2253 individual spiders belonging to 14 families and 41 species), and a total of 3971 individual pests representing 18 families (dominated by Cicadellidae, accounting for 84.01% of the total pests). 2) The richness of the natural enemies in Org was greater than that in Con. The richness of natural enemies in OrgF was higher than that in Con and Org, and the abundance of natural enemies in OrgF was higher than that in Con. 3) In OrgF, the abundance and richness of natural enemies at different distances between the boundary of the paddy field and the interior of the paddy field were significantly different, with a greater richness of natural enemies in the paddy field 5 m away from the field margin than at 20 m. Furthermore, the abundance of natural enemies was significantly lower at the field margins than in paddy fields 5 m away from the boundary. 4) The richness and abundance of natural enemies and pests in paddy fields and their boundaries were positively correlated with vegetation coverage at the paddy field boundary. 5) The ratio of enemies to pests was the highest in the conventional paddy fields (Con), as most pests might be killed by broad-spectrum insecticides, followed by Org and OrgF, which had a large number of pests with only targeted bio-pesticides being used. In conclusion, organic practices in the fields and the flowering boundaries can effectively help to maintain arthropod diversity and increase the diversity of natural enemies in paddy fields. However, to effectively control pests and improve biological control services, an in-depth understanding of the plant-arthropod relationship and careful selection of the “correct” plant diversity are required.