During the last few years, DNA barcoding has become an efficient method for the identification of species. In the case of insects, most published DNA barcoding studies focus on species of the Ephemeroptera, Trichoptera, Hymenoptera and especially Lepidoptera. In this study we test the efficiency of DNA barcoding for true bugs (Hemiptera: Heteroptera), an ecological and economical highly important as well as morphologically diverse insect taxon. As part of our study we analyzed DNA barcodes for 1742 specimens of 457 species, comprising 39 families of the Heteroptera. We found low nucleotide distances with a minimum pairwise K2P distance <2.2% within 21 species pairs (39 species). For ten of these species pairs (18 species), minimum pairwise distances were zero. In contrast to this, deep intraspecific sequence divergences with maximum pairwise distances >2.2% were detected for 16 traditionally recognized and valid species. With a successful identification rate of 91.5% (418 species) our study emphasizes the use of DNA barcodes for the identification of true bugs and represents an important step in building-up a comprehensive barcode library for true bugs in Germany and Central Europe as well. Our study also highlights the urgent necessity of taxonomic revisions for various taxa of the Heteroptera, with a special focus on various species of the Miridae. In this context we found evidence for on-going hybridization events within various taxonomically challenging genera (e.g. Nabis Latreille, 1802 (Nabidae), Lygus Hahn, 1833 (Miridae), Phytocoris Fallén, 1814 (Miridae)) as well as the putative existence of cryptic species (e.g. Aneurus avenius (Duffour, 1833) (Aradidae) or Orius niger (Wolff, 1811) (Anthocoridae)).

In contrast to specific bacterial symbionts of many stinkbugs, which are harboured extracellularly in the lumina of midgut sacs or tubular outgrowths, the obligate endosymbiont of birch catkin bug Kleidocerys resedae (Heteroptera: Lygaeidae) resides in a red-coloured, raspberry-shaped mycetome, localized abdominally, close to the midgut section. Phylogenetic analysis, based on the 16S rRNA gene and the groEL (chaperonin) gene, showed that the bacteria belong to the gamma-subdivision of the Proteobacteria and revealed a phylogenetic relationship with bacterial endosymbionts of Wigglesworthia glossinidia, the primary symbiont of tse-tse fly Glossina brevipalpis. Furthermore, RFLP analysis and sequencing revealed that K. resedae was also infected by Alphaproteobacteria of the genera Wolbachia and Rickettsia. The distribution and transmission of Kleidocerys endosymbiont in adults and all nymph stages were studied using FISH. The detection of symbionts at the anterior poles of developing eggs indicated that endosymbionts are transmitted vertically to offspring. Ultrastructural examinations by electron microscopy revealed the packed accommodation of rod-shaped bacteria in the cytoplasm of mycetocytes. A new genus and species name, 'Candidatus Kleidoceria schneideri', is proposed for this newly characterized clade of symbiotic bacteria.

In the present study, Rickettsia sp. was detected in four water beetles of the genus Deronectes (Dytiscidae) for the first time. Rickettsiae were found in 100% of examined specimens of Deronectes platynotus (45/45), 39.4% of Deronectes aubei (28/71), 40% of Deronectes delarouzei (2/5) and 33.3% of Deronectes semirufus (1/3). Analysis of 16S rRNA gene sequences revealed a phylogenetic relationship with rickettsial isolates of Limonia chorea (Diptera), tentatively classified as members of the basal ancestral group. Phylogenetic analysis of the gltA (citrate synthase) gene sequences showed that Deronectes symbionts were closest to bacterial symbionts from spiders. Ultrastructural examinations revealed typical morphological features and intracellular arrangements of rickettsiae. The distribution, transmission and localization of Rickettsia sp. in D. platynotus were studied using a diagnostic PCR assay and FISH. Eggs from infected females of D. platynotus were all Rickettsia-positive, indicative of a vertical transmission.