Comparison of Dispersion and Regression Indices for Helicoverpa zea (Boddie) [Lepidoptera:noctuidae] on Cotton, in New Mexico

Ahmed A. H. Amin, Zarief R. Sawiers, Tracey Carrillo, Joe Ellington


Dispersion indices, including the k negative binomial distribution, Green's coefficient of dispersion, (C(x)), standardized Morisita's coefficient (IP), mean crowding (m(*)), Lloyd's "Patchiness index" (m(*)/m) and variance mean ratio (s (2)/m), as well as Taylor's regression of log variance against log mean, were calculated for populations of male moths Helicoverpa zea (Boddie) infesting cotton at Las Cruces, NM. Comparisons showed that k, C(x), IP and m(*)/m as well as slopes from regressions all indicated that under the conditions of this test,(at the densities tested), the populations of H. zea were random. 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.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pp. 1031 - 1034
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998