The internal transcribed spacers (ITS1 and ITS2) of the rDNA differentiates the bark beetle forest pests Tomicus destruens and T. piniperda

Abstract

The bark beetles species Tomicus destruens and T. piniperda constitute one of the main pests of European and Asian forests. T. destruens has been thought to be the same species as T. piniperda by some authors. A rapid PCR-based method using internal transcribed spacers (ITS1 and ITS2) of the ribosomal DNA has been developed in order to identifying these two species. We have studied differences in the size of the ITS1, and differences in the sequence and restriction patterns of the ITS2 in 75 individuals of both species. The results indicate a size difference of about 100 bp in the ITS1 of T. destruens and T. piniperda. The size of the ITS2 spacer is similar in both species (approximately 600 bp). However, the sequence is consistently different between T. destruens and T. piniperda in all populations analysed, showing some characteristic indels. Differences in the restriction target in both species for the enzymes HincII and DraI produce different band patterns in agarose NuSieve 5% gel electrophoresis. These data suggest the validity of T. destruens as a phylogenetically differentiated entity from T. piniperda. The phylogenetic analysis of a 789 bp fragment of the 3' end of the cytochrome oxidase I gene (COI) agrees with the two groupings obtained with the ITS2, showing a phylogenetic clustering rather than a phylogeographic structure.

Genetic structure and phylogeography of pine shoot beetle populations (Tomicus destruens and T. piniperda, Coleoptera Scolytidae) in Italy

“…The number of private haplotypes was 3 in T. destruens (A, C, G) and 6 in T. piniperda (4,5,6,8,10,11) (Tab. II).…”

“…As T. destruens has been shown to be associated exclusively with Mediterranean pine species [21], the high fragmentation of the hosts range seems to be the most likely factor explaining the separation of the populations. Conversely, the continuous range of the main host of T. piniperda (P. sylvestris), and the possibility for this species to colonize other hosts and even Mediterranean pines [11,15], appear to be the main reason for the lack of genetic structure [24], in spite of the very numerous private haplotypes found in Italy as well as in other regions.…”

“…However, recent papers reported both morphological and genetic characters useful for the separation of the two siblings [11,15,16]. Nevertheless, species determination by morphological analysis is still extremely difficult, and the genetic support is needed.…”

“…Nevertheless, species determination by morphological analysis is still extremely difficult, and the genetic support is needed. In addition, the sympatry of the two Tomicus in some Mediterranean countries [11,15] makes the identification even more difficult.…”

“…Tomicus species for a host plant does not allow to use host species as a tool for insect identification, although T. destruens was found only on Mediterranean pines so far, whereas T. piniperda was collected from both continental (Pinus sylvestris and P. nigra) and Mediterranean pines (P. pinaster) [11,15].…”