Abstract
Winter-flooding of rice paddies without the application of agricultural chemicals is attracting attention as a new agricultural method for enhancing the habitat conditions of wintering waterfowl in rice paddy ecosystems throughout Japan and east Asia. Conditions in these paddies are expected to result in restoration of not only the winter habitats of waterfowl but also those of other taxonomic groups during the rice growing season. In this study, we tested whether the diversity of summer spiders––ubiquitous predators in rice paddies––was higher in the winter-flooded paddies than in the conventional ones by conducting field measurements in 31 winter-flooded and 7 conventional paddies. Limiting factors of spiders in the winter-flooded paddies were then examined. Results revealed that both the density and species richness of spiders were significantly higher in the winter-flooded paddies than in the conventional ones both before and after the insecticide application against pecky rice bug Stenotus rubrovittatus (Matsumura)(Hemiptera: Miridae) to conventional paddies. In addition, spider density and species richness in the winter-flooded paddies correlated with the availability of two prey groups––chironomids and other nematocera. These findings suggest that in the winter-flooded paddies the diversity of generalist predators is higher than in the conventional ones during the rice-growing season and that the combination of management at both the landscape and field level is likely more effective for increasing spider abundance in winter-flooded paddies.
Highlights
Biological communities in agricultural crop fields that have received low or no chemical application are more diverse than those of conventionally farmed fields (e.g. Bengtsson et al 2005)
We focused on the vegetation structure of rice and abundant weeds, as well as the biomass of abundant arthropod groups, such as chironomidae and other nematocera, brachycera, and hoppers including Cicadellidae and Delphacidae, and the pecky rice bug Stenotus rubrovittatus, as potential limiting factors of the spiders
We examined the limiting factors of spider density and species richness using only the data of the first survey to avoid redundant analyses, because spider density in the WF paddies tended to be higher in the first field survey than in the second and the results obtained from preliminary analyses using the data of the second survey were similar to those of the first survey
Summary
Biological communities in agricultural crop fields that have received low or no chemical application are more diverse than those of conventionally farmed fields (e.g. Bengtsson et al 2005). Rice paddies maintained by biodiversity-friendly farming techniques are expected to function as important substitute habitats for organisms in natural wetlands, which have declined due to the development of urban and agricultural fields (Fasola and Ruiz 1997; Washitani 2007). Crop yield in biodiversity-friendly fields can be low compared with that in paddies that receive conventional chemical applications (de Ponti et al 2012). Identifying the limiting factors of generalist predators in the WF paddies can help with the construction of effective management plans for insect pest control, because our previous studies showed that the spiders predate insect pests (Kobayashi et al 2011; Takada et al 2013), and suppress the density and the consequent damage in organic paddy fields (Takada et al 2012). We focused on the vegetation structure of rice and abundant weeds, as well as the biomass of abundant arthropod groups, such as chironomidae and other nematocera, brachycera, and hoppers including Cicadellidae and Delphacidae, and the pecky rice bug Stenotus rubrovittatus, as potential limiting factors of the spiders
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