To improve the procedures for estimating the abundance of the rice bug, Leptocorisa chinensis Dallas (Heteroptera: Alydidae), field monitoring using traps baited with synthetic attractant was conducted in Tsukuba, central Japan from 2002 to 2006. A mixture of (E)-2-octenyl acetate and 1-octanol, in a ratio of 5 : 1 and incorporated into a plastic pellet, was used as bait on sticky boards and placed at study sites from early June to the end of October. The attractantbaited traps were able to detect the starting of the migration period of the overwintered generation and the population increase of the first generation. The number of trapped insects decreased rapidly after early September, while the number of insects in second generation increased in the grassy weeds field. The decreased temperatures and shorter daylength of autumn (which will have induced reproductive diapause) may have affected the attractiveness of the baited traps. The ratio of males to all captured L. chinensis was 0.88-0.96. Most captured adults had no food in their stomachs, and most males were sexually mature. These results indicate that the males trapped had actively moved for two possible reasons: to search for food and/or to search for females. Based on comparisons between the results of baited trap monitoring and sweep-net surveys, it was considered that immigrant period and density of L. chinenis in the poaceous plants fields depend on the density of dispersal individuals and the heading period of the plants.

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Population subdivision and connectivity within a distribution range are important factors to consider in the development of a management strategy to control widespread pest species. Damage by sorghum plant bug, Stenotus rubrovittatus (Matsumura), has rapidly spread across Japan over the last 10 years. To characterize the fine-scale population structure of this bug and investigate the boundaries of genetic isolation, we analyzed the population structure of 21 local populations within a 72 km 9 200 km area around Fukushima and Ibaraki prefectures. Polymorphism of six microsatellite markers implied that S. rubrovittatus in the study area was divided into northern and southern genetic groups segregated by the 37.3°N line of latitude. The boundary between the two groups, defined by microsatellites, was almost consistent with the range limit of one mitochondrial lineage of the same species. Our result indicated that isolation between these two genetic groups was mediated by historical and ecological origins, and was maintained during the last 10 years when there were rapid outbreaks of this species on rice within the study area.

Abstract:To clarify the timing of the appearance of overwintered and diapausing adults of the rice bug, Leptocorisa chinensis, under natural condition, we adopted two criteria, the developmental stages of gonads and the number of endocuticle layers in the cuticle of the hind-leg femur. Development of gonads after emergence was promoted in adults reared under a long-day photoperiodic condition, but suppressed under a short-day condition. The deposition rate of endocuticle layers was not influenced by the photoperiod but depended on age. These criteria were applied to estimate the annual number of generations of this species in Yamatsuri, Fukushima Prefecture, in 2006. According to these criteria, adults caught in early August, late August and early September were identified as an overwintered, newly-emerged and diapausing individuals, respectively. These data show that L. chinensis has mainly a univoltine life cycle in this region.

Although camera trapping has been effectively used for wildlife monitoring, its application to multihabitat insects (i.e., insects requiring terrestrial and aquatic ecosystems) is limited. Among such insects, perching dragonflies of the genus Sympetrum (darter dragonflies) are agroenvironmental indicators that substantially contribute to agricultural biodiversity. To examine whether custom-developed camera traps for perching dragonflies can be used to assess the relative population density of darter dragonflies, camera trapping, a line-transect survey of mature adult dragonflies, and a line-transect survey of exuviae were conducted for three years in rice paddy fields in Japan. The detection frequency of camera traps in autumn was significantly correlated with the density index of mature adults recorded during the transect surveys in the same season for both Sympetrum infuscatum and other darter species. In analyses of camera-detection frequency in autumn and exuviae in early summer, a significant correlation was observed between the camera-detection frequency of mature adults and the exuviae-density index in the following year for S. infuscatum; however, a similar correlation was not observed for other darter species. These results suggest that terrestrial camera trapping has the potential to be effective for monitoring the relative density of multihabitat users such as S. infuscatum, which shows frequent perching behavior and relatively short-distance dispersal.