Short-sequence fragments ('DNA barcodes') used widely for plant identification and inventorying remain to be applied to complex biological problems. Host-herbivore interactions are fundamental to coevolutionary relationships of a large proportion of species on the Earth, but their study is frequently hampered by limited or unreliable host records. Here we demonstrate that DNA barcodes can greatly improve this situation as they (i) provide a secure identification of host plant species and (ii) establish the authenticity of the trophic association. Host plants of leaf beetles (subfamily Chrysomelinae) from Australia were identified using the chloroplast trnL(UAA) intron as barcode amplified from beetle DNA extracts. Sequence similarity and phylogenetic analyses provided precise identifications of each host species at tribal, generic and specific levels, depending on the available database coverage in various plant lineages. The 76 species of Chrysomelinae included-more than 10 per cent of the known Australian fauna-feed on 13 plant families, with preference for Australian radiations of Myrtaceae (eucalypts) and Fabaceae (acacias). Phylogenetic analysis of beetles shows general conservation of host association but with rare host shifts between distant plant lineages, including a few cases where barcodes supported two phylogenetically distant host plants. The study demonstrates that plant barcoding is already feasible with the current publicly available data. By sequencing plant barcodes directly from DNA extractions made from herbivorous beetles, strong physical evidence for the host association is provided. Thus, molecular identification using short DNA fragments brings together the detection of species and the analysis of their interactions.

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The relative amount of C-banded heterochromatin varies strikingly in seven species of tenebrionid beetles, from 25 to 58%, but most species show procentric bands only. Nevertheless, Gonocephalum patruele exhibits an almost completely heterochromatic X chromosome. The nuclear DNA content of Feulgen-stained spermatids has yielded up to a threefold difference, from 0.27 to 0.86 pg, which is not completely in accordance with the amount of C-banded heterochromatin. However, the genome sizes correlate significantly with the total chromosome areas at metaphase I and with the spermatid areas. Furthermore, the genome sizes agree with the subfamilial taxonomic groupings of these tenebrionids.Key words: Tenebrionidae, genome size, C-banding.

In situ hybridization to chromosomes and nuclei of Tenebrio molitor shows the massive presence of a species-specific satellite DNA in all chromosomes and six sites of rDNA in mitotic chromosomes. These sites are located in two autosomal pairs and in the X and Y chromosomes. In a related species, Misolampus goudoti, in which two different families of highly repetitive DNA have been previously characterized, one family is located in centromeric regions of all chromosomes with the exception of chromosome Y, while the other repeated DNA family is present both in centromeric and distal regions of all chromosomes. rRNA genes in this species are present in a medium-sized autosomal pair only. These results show that molecular cytogenetics can be applied to coleopteran chromosomes and open the way for a physical mapping of DNA sequences in these organisms. The results also provide insights into the type of meiotic association of the X and Y chromosomes in Coleoptera and the distribution of repeated DNAs within the genome of these insects.

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