Comparison of Dispersion and Regression Indices for Tetranychus cinnabarinus (Boisduval) (Acari: Tetranychidae) Populations in Cotton

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Abstract
Dispersion indices, including Green's coefficient of dispersion ( Cx ), the standardized Morisita's coefficient ( Ip ), mean crowding (m*), Lloyd's “patchiness index” (m*/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 m*/ 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.

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