Analysis of spatial relations of Dialeurodes citri and its principal natural enemies

Although somehow influenced by sampling size, the aggregated intensity index was used to assess the spatial distribution of pests and their natural enemies and eventually used to determine the relationship between pests and their natural enemies. To analysis the degree of closeness of the spatial relations of natural enemies to Dialeurodes citri and the cause-range aggregation, the block-quadrat variance analysis, grey correlaiton analysis, aggregated intensity index analysis, aggregated population mean analysis and the ρ index analysis were used to study D. citri and 6 of its dominant natural enemies from a total of 11 species of natural enemies under different poly block sizes (namely, different basic quadrats numbers in a poly block) in tea gardens in Qianshan Area, Anhui Province. The study may provide scientific basis for determining the dominant natural enemy species of D. citri. The grey correlation degree analysis showed that the most closely followed natural enemies of D. citri were Erigonidium graminicolum (0.848 6), Theridion octomaculatum (0.840 6) and Propylaea japonica (0.805 5). However, the spatial following relation of Chilocorus kuwanae (0.764 2) with D. citri was not so close. The synthetic block-quadrat variance and aggregate intensity analysis results suggested that by increasing basic quadrat number within the poly block from 1 to 8, the diffusion coefficient C of aggregation pattern increased, while the diffusion coefficient C of uniform and random aggregation patterns decreased. In addition, the aggregation degree of spatial distribution of D. citri and its natural enemies had no significant difference between basic quadrat number 1 and basic quadrat number 2, 4, 8, 16 and 32. The average λ of D. citri was higher than 2, suggesting self-aggregation of D. citri. When average λ was positive, the gathering average of population steadily increased with increasing basic quadrat number within the poly block. The ρ index analysis suggested that the minimum area of aggregation pattern of D. citri was one basic quadrat of 1.7 m². Put together, the results provided a critical basis for further protection of natural enemies and determination of suitable quadrat sizes of pest sampling.