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Comparison of Dispersion and Regression Indices forTetranychus cinnabarinus(Boisduval) (Acari: Tetranychidae) Populations in Cotton
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1984
Year
Dispersion indices, including Green's coefficient of dispersion ( Cx ), the standardized Morisita's coefficient ( Ip ), mean crowding (<mml:math><mml:mrow><mml:mover><mml:mi>m</mml:mi><mml:mo>*</mml:mo></mml:mover></mml:mrow></mml:math>), Lloyd's “patchiness index” (<mml:math><mml:mrow><mml:mover><mml:mi>m</mml:mi><mml:mo>*</mml:mo></mml:mover></mml:mrow></mml:math>/m) and variance/mean ratio ( s2 / m ), as well as Iwao's regression of m against the mean and Taylor's regression of log variance against log mean, were calculated for populations of female Tetranychus cinnabarinus (Boisduval) infesting cotton. Comparisonhs show that Cx, Ip and <mml:math><mml:mrow><mml:mover><mml:mi>m</mml:mi><mml:mo>*</mml:mo></mml:mover></mml:mrow></mml:math>/ m as well as slopes from the regressions all indicated that the population was slightly aggregated. The variance/mean ratio fluctuated considerably more than other indices examined, which, when coupled with a strongly dependent relationship with the mean, suggested that this index may be less reliable than previously thought.