A sampling procedure for quantifying mites in soybeans

Abstract

To control phytophagous mites on soybean crops in an economically viable way, it is necessary to quantify the occurrence of the mites on the leaflets. Estimating the number of mites cm(-2) on leaflets is more difficult because of their irregular distribution on the leaflet surface. Therefore, the aim of this study was to determine the count-area/leaflet and the number of soybean leaflets to quantify the mites. One hundred infested plants were randomly collected. One leaflet was removed from each plant and divided into 32 sections (1.0 cm(2) per section), arranged in four columns and eight rows, to count the mites (adults, nymphs and eggs). The ideal count-area size per leaflet (Xo) was estimated by the maximum curvature of the coefficient of variation method for each of the 100 leaflets. For a count-area of Xo size, we obtained the number of mites cm(-2) per leaflet and, using the bootstrap resampling method, we estimated the point and interval averages as well as the sample size for a pre-established error. We suggest that the determination of the evaluated area size on each soybean leaflet (20 cm(2) in this case) and the bootstrap resampling estimate of the appropriate number of leaflets (12 in this case) for a bootstrap confidence interval of four mites (adults + nymphs) cm(-2) is sufficient to standardize the sampling-procedures for quantifying mites on soybean leaflets.

Comparison of beat cloth and entomological net methods for determining faunistic indices of soybean in Rio Grande do Sul, Brazil

“…For each of the faunistic indices and sampling methods, the sample size (number of quadrants) necessary to estimate the faunistic indices based on an estimation error of 20 % of the average with a 5 % error probability was estimated using the bootstrap resampling method (Efron, 1979) and applied as indicated in Storck et al (2012). In this procedure, 2,000 resamplings with replacements were repeated for different resamplings sizes or numbers of quadrants (k = 3, 4, ..., 300).…”

Tamanho de amostra para avaliar a densidade populacional de percevejos em lavouras de soja

“…O tamanho de amostra foi obtido pelo método de reamostragem (EFRON, 1979;FERREIRA, 2005;STORCK et al, 2012). Esse método é adequado, tendo em vista que os valores do número de insetos por ponto (densidade populacional), em geral, não seguem distribuição de probabilidade conhecida ou não é a mesma para os diferentes ambientes, método de coleta e espécies (BARBOSA, 2001).…”

Tamanho de amostra para avaliar a densidade populacional de lagartas em lavouras de soja

“…Para cada uma das 100 lavouras, cada método de coleta e cada espécie, foi estimada a média e determinado o tamanho de amostra pelo método de reamostragem (Efron 1979, Ferreira 2005, Storck et al 2012. Esse procedimento estatístico é adequado, tendo em vista que os valores do número de insetos por ponto (densidade populacional), em geral, não seguem distribuição de probabilidade conhecida ou não, e é a mesma para os diferentes ambientes, método de coleta e espécies (Barbosa 2001).…”