Abstract
The Tetranychidae family or spider mites comprises a large group of phytophagous mites with many of its species considered as important pests of agricultural crops worldwide. The two-spotted spider mite, Tetranychus urticae Koch (Prostigmata: Tetranychidae), an ubiquitous species causing outbreaks in many crops, is certainly the most studied species. Many aspects of its systematic, biology, feeding habits, and control have been studied. In Brazil, T. urticae is considered as one of the three main mite pests. Despite the unquestionable progress on tetranychid studies in the country, it is essential to gain in knowledge of these mites from unexplored regions or crops. The use of molecular tools to study phylogentic relationship among species and also population genetic structure of key pest species, such as T. urticae would enhance the understanding of the family. In this study we performed a survey of Tetranychidae mites from Brazil, including 15 States and the Federal District. A total of 550 samples of 120 different plant species were collected. Tetranychid mite infestations were confirmed in 207 samples, and 22 species belonging to seven genera of the Bryobiinae and Tetranychinae subfamilies were identified on 58 different host plants. Thirty-six new hosts for the Tetranychidae were recorded in Brazil, South America and worldwide for eleven species. New localities were registered for four tetranychid genera and a new record to South America was confirmed. Four species were identified as new for science: two belonging to the Oligonychus Berlese genus, on grape (Vitis vinifera L.) and rose (Rosa sp.) from Minas Gerais; and two belonging to the Monoceronychus McGregor and Schizotetranychus Tragardh genera, both from weeping fingergrass (Eustachys distichophylla Lag. Nees) from Rio Grande do Sul. We also analyzed sequences of the genus Tetranychus deposited in databases. We analyzed and evaluated the identity of 105 Genbank accessions of ITS2 rDNA and 138 COI mtDNA sequences which were deposited as T. urticae and as fourteen other taxa morphologically closely related to Tetranychus sensu stricto. In addition, ITS2 and COI sequences of 18 T. urticae samples unambiguously identified by morphological criteria were generated in this study and included in the analyzed dataset. Among the deposited sequences in the Genbank, numerous cases of apparently mistaken identities were identified in the group Tetranychus s. str., especially between T. urticae, T. cinnabarinus, T. kanzawai and T. truncatus. The results suggest that nearly 30% of the studied sequences may be unreliable (misidentified or dubious). In particularly this study sheds new light on the controversial taxonomic status of T. cinnabarinus and highlights the need of using combined morphological and molecular approaches to guaranty reliability of accessions in public databases. Information on genetic variability and structure of T. urticae populations from Brazil and worldwide was also performed. New sequences of ITS and COI were obtained from individuals collected in Brazil and some localities of the Palearctic Region (France, continental Spain, Canary Islands, Greece, Syria, Tunisia, Poland and Norway – plus one from x Canada). While significant differences were detected on population genetic structure of the analyzed samples according to the geographic region, any effect of the host plant was observed. Haplotype diversity inferred from both ITS and COI sequences was higher in samples from the Mediterranean basin. ITS sequences obtained from Brazil samples were homogenous, and two COI haplotypes were found, one of them also present in France, Spain and the Canary Islands and the other in Japan.