SummaryTetranychus urticae is a polyphagous mite which is an important pest of citrus worldwide. This mite can be found feeding on many plant species occurring in the citrus agrosystem moving from weeds to trees. Because field samples consist of a mixture of different Tetranychidae species, as a first step necessary to further implement population characterization of T. urticae, species-discriminating criteria based on molecular techniques are needed. In this study, the nucleotide variation of the Internal Transcribed Spacers (ITS) 1 and 2 and the intergenic 5.8S fragment of nuclear ribosomal DNA of T. urticae, T. turkestani, T. evansi, T. ludeni and P. citri, have been determined. Results demonstrate that for these species, the rDNA ITS2 regions are much more conserved than the corresponding rDNA ITS1. The high homogeneity of the ITS2 sequence observed among the specimens of T. urticae obtained from the same eco-region makes this DNA-sequence an excellent tool for species discrimination. ITS sequences differentiate not only species but also specimens from different geographical origin. Furthermore, PCR-RFLP analysis of the ITS2 proved adequate for a quick screening of high numbers of field samples.

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The relationship between the number of immature individuals of Tetranychus urticae used to calculate life table parameters (sex ratio, development time, immature survival and the intrinsic rate of increase) and the accuracy of such determinations has been estimated. Additionally, the approach used in this paper, which considers each female offspring as a separate replicate, has allowed statistical comparison of the parameters obtained. At least the first four eggs from 16 females should be followed up to completion of their development to prevent the occurrence significant differences for the selected parameters. However, our results indicate that optimal sample sizes are different for the different life table parameters considered and should adapt to the preset level of accuracy.