Spatial distribution of adult Anthonomus grandis Boheman (Coleoptera: Curculionidae) and buds with feeding punctures on conventional and Bt cotton

Abstract

Dispersion patterns of Anthonomus grandis adults and damaged squares with their feeding punctures are important to enhance pest monitoring and control on cotton. In this research we performed probabilistic analyses of the distribution patterns of adults and squares with feeding punctures of A. grandis on two cotton genotypes, Bt and non-Bt near isogenic lines. We conducted the field experiment in two experimental areas; each area had 100 plots composed of seven rows, each seven metros long. Between Jan and May 2010, 16 samplings were made, in each, five plants were evaluated per plot by counting the adults and damaged squares. The dispersion indexes (ratio of the variance/mean, the Morisita index, and Exponent k of the Binomial Negative Distribution) and the theoretical distribution of frequencies (Poisson, Negative Binomial and Positive Binomial) were calculated. No differences between cotton genotypes were found. The spatial distribution of A. grandis adults fit the Negative Binominal (aggregate) and Positive Binominal (uniform) distributions, depending on the number of days after cotton emergence. The dispersion analyses of the feeding damaged squares on the Bt and conventional cotton revealed Poisson (random), Negative Binominal (aggregate) and Positive Binominal (uniform) distribution patterns in sequence during the crop cycle.