Distribution patterns of and sampling plans forTetranychus urticae Koch (Acarina: Tetranychidae) on roses

Summary

I sampledTetranychus urticae Koch (Acarina: Tetranychidae) regularly from four rose gardens in Kyoto and Nara Prefectures in 1988–1990. When mite density was low,T. urticae showed an uneven vertical distribution, being more abundant in the lower third and absent from the upper third of the plants. Mite density was less variable within than between plants, suggesting that a sampling plan which includes more leaves from different plants rather than from different levels of a plant is favourable. Spatial distribution ofT. urticae was nonrandom and followed the negative binomial distribution. In addition, both the Taylor’s power law and the Iwao’s patchiness regression described the distribution well. An empty-sample method for estimating mite density from the proportion of empty sampling units was developed. Sampling plans for determining the sample size required to reach a predetermined precision level, based on this method and by directly counting the mites, were designed. The counting method was more accurate than the empty-sample method. However, when the time factor was taken into account, the latter was more favourable, because it was faster than the former at a density range of 1.5–300 mites leaf⁻¹, which was most commonly encountered in the field.