Studies on the population dynamics of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (coleoptera: curculionidae).

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  • イネミズゾウムシの個体群動態と平衡密度
  • イネミズゾウムシ ノ コタイグン ドウタイ ト ヘイコウ ミツド

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Population dynamics of the rice water weevil was studied in paddy fields from 1978 to 1983 in association with some laboratory experiments. Oviposition experiments with potted rice plants indicated that the fecundity decreased with the increase in the density of parthenogenic females above 2 adults per hill. The mean fecundity was 75-78 eggs per female with a maximum of 120 eggs. Key-factor analysis suggested that the mortality rate from egg to young larva was the key factor determining the mortality rate from egg to adult emergence in a generation. On the other hand, the mortality rate from mature larva to cocoon contributed to a lesser extent to the mortality rate in a generation. These mortality rates were density-dependent in relation to the population density in the respective stages. The population density of this weevil, therefore appears to be regulated mainly by density-dependent processes that operate during the time interval from oviposition of adults to the emergence of young larvae. The pattern of population growth can be simulated by a logistic equation. Equilibrium densities of overwintering adults in the paddy fields, however, seemed to be determined by the availability of favorable overwintering sites which depended on the topographical conditions of the area concerned. The equilibrium densities were estimated at 0.38, 1.78 and 2.44 overwintering parthenogenetic females per hill in coastal plain, interior hilly and mountain areas, respectively.

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