Epitrix species (Coleoptera: Chrysomelidae) feed mostly on plants from the family Solanaceae and some of them are major pests of potato crops. All Epitrix species are morphologically highly similar, which makes them difficult to identify and limits their study and management. Identification of species is mostly based on the observation of the genitalia and requires a high level of expertise. Here, we propose a tool to reliably identify all developmental stages of the most economically important Epitrix species feeding on potato in Europe and North America (Epitrix cucumeris, Epitrix similaris, Epitrix tuberis, Epitrix subcrinita and Epitrix hirtipennis). We first sequenced two DNA markers (mitochondrial cytochrome c oxidase I (COI) and nuclear internal transcribed spacer 2 (ITS2)) to test their effectiveness in differentiating among six Epitrix species (126 specimens). Morphospecies of Epitrix were well-differentiated by both DNA barcodes and no mitochondrial introgression was detected. Then, we developed an RFLP-based diagnostic method and showed that unambiguous species discrimination can be achieved by using the sole restriction enzyme TaqI on COI polymerase chain reaction products. The tool proposed here should improve our knowledge about Epitrix species biology, distribution and host range, three capacities that are particularly important in the detection and management of these pest species. Specifically, this tool should help prevent the introduction of E. tuberis and E. subcrinita in Europe and limit the spread of the recently introduced E. cucumeris and E. similaris, with minimal disruption to Solanaceae trade.

Ants (Hymenoptera: Formicidae) are important predators of herbivorous insects on plants (Rosumek et al. 2009). Ant removal or absence may result in negative indirect effects on plants, as herbivore abundance and herbivory increase and plant growth and reproduction decline (Rosumek et al. 2009, Schmitz et al. 2000). Ant presence on plants often results from a mutualistic interaction. For example, strong highly coevolved ant–plant mutualisms are found on myrmecophytic plants that house ants in domatia (specialized nesting sites). Weaker mutualistic associations are found with myrmecophilic plants that only offer extra-floral nectaries (EFNs) or food bodies to attract ants, or on other plants hosting honeydew-producing hemipterans (indirect ant–plant interactions) that mediate ant abundance (Hölldobler & Wilson 1990). However, in most cases, plants and arboreal ants form more passive associations, where ants nest in the natural cavities of branches or bark, or construct carton nests on plant substrates (Hölldobler & Wilson 1990) and the only reward plants offer these ants is the use of their substrates. In these situations the indirect effect of ants on plants is merely by chance, a byproduct of ant presence (byproduct association).