Spatial Distribution Pattern of the Low Density Populations of Aphids in the Corn Fields

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  • トウモロコシに寄生するアブラムシ類の低密度個体群の空間分布構造
  • トウモロコシ ニ キセイスル アブラムシルイ ノ テイ ミツド コタイグン ノ

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Abstract

Population dynamics of three species of aphids, (Rhopalosiphum padi, R. maidis and Macrosiphum akebiae), was observed in the unsprayed corn fields for three years. Any actual injuries on plants by pest insects had not been observed over fifteen years in this field. The density of aphids on a plant was very low in each year of observation. Even at the peak of population fluctuation, the mean number per plant was below ten individuals. The population of aphids declined from mid June and became very scarce or disappeared in early July in each year. The autumn population was also at a very low density. The spatial distribution of alatae was random or uniform whenever the size of sampling unit was taken as plot (20 plants), plant, and leaf. The distribution of apterae and larvae was highly contagious regardless of the difference in the size of sampling unit. On a plant the aphid of each species generally inhabited on the leaves grown at low portion. The habitat segregation among the three species of aphids in a plant was not recognized. It seems that such a distribution pattern is diagnostic character of low density population of aphids.

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