Dynamics Of The Important Insect Pests And Arthropod Diversity In The Fish-lotus Symbiotic System Fields

Nelumbo nucifern Gaertn is an aquatic vegetable which occupies the largest planting area among all the aquatic vegetables in China. But there was little studies done about the arthropod and pests in the ecosystem. The fish-lotus symbiotic system, as an old ecological model been applied for years, has been proven effective to the controlling of pests on lotus. However, the related studies just stay on the surface. In this study, the fishes of different densities and species were put into the lotus field, and the occurrence and the population dynamics of the arthropod were regularly investigated, and the arthropod diversity impacted by different fish densities were discussed. The potential economic benefit of the fish-lotus symbiotic was discussed in detail. Moreover, the population dynamics and behavioral characteristics of major pests, such as Donacia provostii, were studied, and the control viability of these pests in the fish-lotus symbiotic system was furtherly discussed. The main results are summarized as follows:(1) The arthropod diversity in lotus field at different stocking fish density treatments:The fish-lotus symbiotic system did not affect the composition and the richness of arthropod, but it significantly affected the individual number of Rhopalosiphum nymphaeae, Pirata subpiraticus and Chironomidae pests. The different density of fishes had certainly affected on the nutrition functional group structure of arthropod in N. nucifern field, mainly being demonstrated on the larger number of phytophagous arthropod in fish-lotus symbiotic system. This was probably due to the number of major pests such as R. nymphaeae was reduced, and the competitive pressure of food for other phytophagous arthropod was also reduced in the fish-lotus symbiotic system.(2) The composition and seasonal dynamics of arthropod at different fish density treatments:The primary pests in N. nucifern field are R. nymphaeae and Prodenia litura, and the primary natural enermies is P. subpiraticus. No significant difference showed in seasonal dynamics of primary pests as well as natural enemies in the field at different fish density treatment, including species number, individual amount and the percentage of the most dominant species. But there were significant impacts on the number of R. nymphaeae, P. subpiraticus and Chironomidae pests in different periods.(3) The niche of primary pests and natural enemies in the fish-lotus symbiotic system:The time niche of main pests and natural enemies influenced by different fish density is more significantly the spatial niche. The time niche breadth had most significant effect in main pests and natural enemies including R. nymphaeae, p. litura, Chironomidae pests and Pirata subpiraticus, and had more significant effect on spatial niche breadth for other spider groups.(4) The economic benefit of fish-lotus symbiotic system:Through a systematic study in detail, the results showned that the optimal economic benefit of the fish-lotus symbiotic system is closely related to the density and the species of fish. And the common carp fish maybe is the most optimum for release in terms of economic effectiveness.(5) The annual population dynamics and behavioral characteristics of an important pest, Donacia provostii:The annual dynamic investigation showed that the adult exsisted in changsha area from mid-april to late September, which proved that this species happened many generations one year and existed serious generation overlapping phenomenon in Changsha area. The further study to the rhythm of D. provostii indicates the behavior is significantly different in time point and time period, and the the percentage of behavior is also significantly different in different positions. The difference of behavior is shown in temporal and spatial, and the behavior is more obovious influenced by spatial. Behavioral characteristics on different host determined the difference of its governance approach and ease, the study of D. provostii provides basic scientific data for construsting effective control technology system to this pest.