Summary Popillia japonica Newman (Coleoptera: Scarabaeidae) is a highly polyphagous invasive beetle originating from Japan. This insect is highly resilient and able to rapidly adapt to new vegetation. Insect‐associated microorganisms can play important roles in insect physiology, helping their hosts to adapt to changing conditions and potentially contributing to an insect's invasive potential. Such symbiotic bacteria can be part of a core microbiota that is stably transmitted throughout the host's life cycle or selectively recruited from the environment at each developmental stage. The aim of this study was to investigate the origin, stability and turnover of the bacterial communities associated with an invasive population of P. japonica from Italy. Our results demonstrate that soil microbes represent an important source of gut bacteria for P. japonica larvae, but as the insect develops, its gut microbiota richness and diversity decreased substantially, paralleled by changes in community composition. Notably, only 16.75% of the soil bacteria present in larvae are maintained until the adult stage. We further identified the micro‐environments of different gut sections as an important factor shaping microbiota composition in this species, likely due to differences in pH, oxygen availability and redox potential. In addition, P. japonica also harboured a stable bacterial community across all developmental stages, consisting of taxa well known for the degradation of plant material, namely the families Ruminococcacae, Christensenellaceae and Lachnospiraceae. Interestingly, the family Christensenallaceae had so far been observed exclusively in humans. However, the Christensenellaceae operational taxonomic units found in P. japonica belong to different taxonomic clades within this family.

In the contest of global biodiversity loss, molecular species delimitation approaches can be very useful for accelerating species discovery through DNA taxonomy and inventory through DNA metabarcoding. In this study, the effect of some intrinsic factors on the efficiency of various single-marker species delimitation methods (fixed and variable nucleotide distance thresholds, ABGD, ASAP, GMYC, mPTP) was tested on more than empirical datasets, derived from a set of 7,237 COI sequences attributed to leaf beetles species (Coleoptera: Chrysomelidae). The considered factors were: i) the number of haplotypes per species (as a proxy for genetic diversity); ii) the geographic distance among conspecific collection localities (as a proxy of sampling width); iii) the difficulty related to morphological identification of species; iv) the taxonomic rank. Distance-based methods, with on average more than 70% of match with morphological identification, outperformed those relying on phylogenetic trees, with less than 59%. A high number of haplotypes per species was found to have a negative effect on delimitation efficiency, whereas large geographic distances within species had a positive effect. All methods delimitations (except for GMYC) were significantly affected by the presence of species that are difficult to be identified, decreasing their efficiency. Finally, the only method influenced by the taxonomic rank of the dataset was GMYC, showing lower efficiency in datasets at the genus than at higher levels. The observed biases we highlighted affecting efficiency could be accounted for when developing input datasets for species delimitation analyses to obtain a more reliable representation of biological diversity.

Insects are a highly diverse group of organisms and constitute more than half of all known animal species. They have evolved an extraordinary range of traits, from flight and complete metamorphosis to complex polyphenisms and advanced eusociality. Although the rich insect fossil record has helped to chart the appearance of many phenotypic innovations, data are scarce for a number of key periods. One such period is that following the End-Permian Extinction, recognized as the most catastrophic of all extinction events. We recently discovered several 240-million-year-old insect fossils in the Mount San Giorgio Lagerstätte (Switzerland–Italy) that are remarkable for their state of preservation (including internal organs and soft tissues), and because they extend the records of their respective taxa by up to 200 million years. By using these fossils as calibrations in a phylogenomic dating analysis, we present a revised time scale for insect evolution. Our date estimates for several major lineages, including the hyperdiverse crown groups of Lepidoptera, Hemiptera: Heteroptera and Diptera, are substantially older than their currently accepted post-Permian origins. We found that major evolutionary innovations, including flight and metamorphosis, appeared considerably earlier than previously thought. These results have numerous implications for understanding the evolution of insects and their resilience in the face of extreme events such as the End-Permian Extinction.

Leaf beetles (Coleoptera: Chrysomelidae), with more than 37,000 species worldwide and about 2,300 in the Euro-Mediterranean region, are an ecological and economical relevant family, making their molecular identification of interest also in agriculture. This study, part of the Mediterranean Chrysomelidae Barcoding project (www.c-bar.org), aims to: (i) develop a reference Cytochrome c oxidase I (COI) library for the molecular identification of the Euro-Mediterranean Chrysomelidae; (ii) test the efficiency of DNA barcoding for leaf beetles identification; (iii) develop and compare optimal thresholds for distance-based identifications estimated at family and subfamily level, minimizing false positives and false negatives. Within this study, 889 COI nucleotide sequences of 261 species were provided; after the inclusion of information from other sources, a dataset of 7,237 sequences (542 species) was analysed. The average intra-interspecific distances were in the range of those recorded for Coleoptera: 1.6–24%. The estimated barcoding efficiency (~94%) confirmed the usefulness of this tool for Chrysomelidae identification. The few cases of failure were recorded for closely related species (e.g., Cryptocephalus marginellus superspecies, Cryptocephalus violaceus - Cryptocephalus duplicatus and some Altica species), even with morphologically different species sharing the same COI haplotype. Different optimal thresholds were achieved for the tested taxonomic levels, confirming that group-specific thresholds significantly improve molecular identifications.

Plants generate energy flows through natural food webs, driven by competition for resources among organisms, which are part of a complex network of multitrophic interactions. Here, we demonstrate that the interaction between tomato plants and a phytophagous insect is driven by a hidden interplay between their respective microbiotas. Tomato plants colonized by the soil fungus Trichoderma afroharzianum , a beneficial microorganism widely used in agriculture as a biocontrol agent, negatively affects the development and survival of the lepidopteran pest Spodoptera littoralis by altering the larval gut microbiota and its nutritional support to the host. Indeed, experiments aimed to restore the functional microbial community in the gut allow a complete rescue. Our results shed light on a novel role played by a soil microorganism in the modulation of plant–insect interaction, setting the stage for a more comprehensive analysis of the impact that biocontrol agents may have on ecological sustainability of agricultural systems.