Intraspecific variations in life history traits of two pecky rice bug species from Japan: Mapping emergence dates and number of annual generations

The mirid bugs Stenotus rubrovittatus and Trigonotylus caelestialium, which cause pecky rice, have become a threat to rice cultivation in Asia. Damage caused by these pests has rapidly become frequent since around 2000 in Japan. Their expansion pattern is not simple, and predicting their future spread remains challenging. Some insects with wide ranges have locally adapted variations in life-history traits. We performed laboratory rearing experiments to assess the geographical scale of intraspecific variations in life-history traits of S. rubrovittatus and T. caelestialium. The experiments were aimed at increasing the accuracy of occurrence estimates and the number of generations per year. These results were compared with previous research, and differences in development rates were observed between populations of different latitudes, but not of the same latitude. Finally, plotting the timing of adult emergence and the potential number of generations per year on maps with a 5-km grid revealed that they differed greatly locally at the same latitude. These maps can be used for developing more efficient methods of managing mirid bugs in integrated pest management.

Occurrence patterns of crop-foraging sika deer distribution in an agriculture-forest landscape revealed by nitrogen stable isotopes

Conflicts arising from the consumption of anthropogenic foods by wildlife are increasing worldwide. Conventional tools for evaluating the spatial distribution pattern of large terrestrial mammals that consume anthropogenic foods have various limitations, despite their importance in management to mitigate conflicts. In this study, we examined the spatial distribution pattern of crop-foraging sika deer by performing nitrogen stable isotope analyses of bone collagen. We evaluated whether crop-foraging deer lived closer to agricultural crop fields during the winter and spring, when crop production decreases. We found that female deer in proximity to agricultural crop fields during the winter and spring were more likely to be crop-foraging individuals. Furthermore, the likelihood of crop consumption by females decreased by half as the distance to agricultural crop fields increased to 5-10 km. We did not detect a significant trend in the spatial distribution of crop-foraging male deer. The findings of spatial distribution patterns of crop-foraging female deer will be useful for the establishment of management areas, such as zonation, for efficient removal of them.

A global synthesis reveals biodiversity-mediated benefits for crop production

Human land use threatens global biodiversity and compromises multiple ecosystem functions critical to food production. Whether crop yield-related ecosystem services can be maintained by a few dominant species or rely on high richness remains unclear. Using a global database from 89 studies (with 1475 locations), we partition the relative importance of species richness, abundance, and dominance for pollination; biological pest control; and final yields in the context of ongoing land-use change. Pollinator and enemy richness directly supported ecosystem services in addition to and independent of abundance and dominance. Up to 50% of the negative effects of landscape simplification on ecosystem services was due to richness losses of service-providing organisms, with negative consequences for crop yields. Maintaining the biodiversity of ecosystem service providers is therefore vital to sustain the flow of key agroecosystem benefits to society.

Detecting crucial dispersal pathways using a virtual ecology approach: A case study of the mirid bug Stenotus rubrovittatus

Detecting dispersal pathways is important both for understanding species range expansion and for managing nuisance species. However, direct detection is difficult. Here, we propose detecting these crucial pathways using a virtual ecology approach, simulating species dynamics using models, and virtual observations. As a case study, we developed a dispersal model based on cellular automata for the pest insect Stenotus rubrovittatus and simulated its expansion. We tested models for species expansion based on four landscape parameters as candidate pathways; these are river density, road density, area of paddy fields, and area of abandoned farmland, and validated their accuracy. We found that both road density and abandoned area models had prediction accuracy. The simulation requires simple data only to have predictive power, allowing for fast modeling and swift establishment of management plans.

Comparison of generalist predators in winter-flooded and conventionally managed rice paddies and identification of their limiting factors

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.