Background: Various methods have been proposed to assign unknown specimens to known species using their DNA barcodes, while others have focused on using genetic divergence thresholds to estimate “species” diversity for a taxon, without a well-developed taxonomy and/or an extensive reference library of DNA barcodes. The major goals of the present work were to: a) conduct the largest species-level barcoding study of the Muscidae to date and characterize the range of genetic divergence values in the northern Nearctic fauna; b) evaluate the correspondence between morphospecies and barcode groupings defined using both clustering-based and threshold-based approaches; and c) use the reference library produced to address taxonomic issues.Results: Our data set included 1114 individuals and their COI sequences (951 from Churchill, Manitoba), representing 160 morphologically-determined species from 25 genera, covering 89% of the known fauna of Churchill and 23% of the Nearctic fauna. Following an iterative process through which all specimens belonging to taxa with anomalous divergence values and/or monophyly issues were re-examined, identity was modified for 9 taxa, including the reinstatement ofPhaonia luteva(Walker)stat. nov.as a species distinct fromPhaonia errans(Meigen). In the post-reassessment data set, no distinct gap was found between maximum pairwise intraspecific distances (range 0.00-3.01%) and minimum interspecific distances (range: 0.77-11.33%). Nevertheless, using a clustering-based approach, all individuals within 98% of species grouped with their conspecifics with high (>95%) bootstrap support; in contrast, a maximum species discrimination rate of 90% was obtained at the optimal threshold of 1.2%. DNA barcoding enabled the determination of females from 5 ambiguous species pairs and confirmed that 16 morphospecies were genetically distinct from named taxa. There were morphological differences among all distinct genetic clusters; thus, no cases of cryptic species were detected.Conclusions: Our findings reveal the great utility of building a well-populated, species-level reference barcode database against which to compare unknowns. When such a library is unavailable, it is still possible to obtain a fairly accurate (within ~10%) rapid assessment of species richness based upon a barcode divergence threshold alone, but this approach is most accurate when the threshold is tuned to a particular taxon.

Estimations of tropical insect diversity generally suffer from lack of known groups or faunas against which extrapolations can be made, and have seriously underestimated the diversity of some taxa. Here we report the intensive inventory of a four-hectare tropical cloud forest in Costa Rica for one year, which yielded 4332 species of Diptera, providing the first verifiable basis for diversity of a major group of insects at a single site in the tropics. In total 73 families were present, all of which were studied to the species level, providing potentially complete coverage of all families of the order likely to be present at the site. Even so, extrapolations based on our data indicate that with further sampling, the actual total for the site could be closer to 8000 species. Efforts to completely sample a site, although resource-intensive and time-consuming, are needed to better ground estimations of world biodiversity based on limited sampling.

The Canadian Diptera fauna is updated. Numbers of species currently known from Canada, total Barcode Index Numbers (BINs), and estimated numbers of undescribed or unrecorded species are provided for each family. An overview of recent changes in the systematics and Canadian faunistics of major groups is provided as well as some general information on biology and life history. A total of 116 families and 9620 described species of Canadian Diptera are reported, representing more than a 36% increase in species numbers since the last comparable assessment by JF McAlpine et al. (1979). Almost 30,000 BINs have so far been obtained from flies in Canada. Estimates of additional number of species remaining to be documented in the country range from 5200 to 20,400.

The adult of a new genus and new species of Muscidae, Callainireinwardtia woodi sp. nov, gen. nov., is described from Costa Rica. This new genus is placed in the tribe Reinwardtiini and can be distinguished from other members of the group as well as other New World Muscidae by the presence of a striking blue to blue-green metallic color combined with a bare anepimeron, setulose metepisternum, a plumose arista, and wings without clouds or spots. Conflicting data on the phylogenetic position of the reinwardtiine genera is summarized and potential avenues for future research are suggested.

Climate change rapidly drives species range dynamics, prompting many terrestrial organisms to shift northward to higher latitudes and forcing new species–species and species–environment interactions. The blacklegged tick, Ixodes scapularis , a biological vector of human pathogens including Borrelia burgdorferi (the bacteria causing Lyme disease), is undergoing rapid and persistent expansion into Canada, exposing new human populations to zoonotic diseases. Here, we used an ensembled forecasting approach to construct niche models of I. scapularis' current and future distribution and to identify the environmental drivers of habitat range. Georeferenced occurrence points were acquired from community science programs (eTick and iNaturalist) between 2017 and 2022 in Canada and the United States. We also collected high‐resolution environmental data using a spacing of approximately 1 km. We carried out 4704 model iterations across two datasets, 12 algorithms, and 10 climate profiles using 40 environmental variables. We extrapolated select models over three time periods, 2011–2040, 2041–2070, and 2071–2100, across two projected climate scenarios, SSP5‐8.5 and SSP3‐7.0, incorporating 2094 future outcomes of I. scapularis distribution. Our ensembles (AUC: 0.9565 ± 0.0065; TSS: 0.8435 ± 0.0155; Kappa: 0.819 ± 0.014) identified temperature, precipitation, biomass production (NPP), length of the growing season, climate moisture index, and number of yearly degree days as the variables that best explained I. scapularis distribution. Further changes to these climate conditions will result in continued I. scapularis range expansion, with, at the highest estimate, an increased niche area of ~248% (447,532 km ² to 1,556,760 km ² ) and, at the lowest estimate, by ~205% (409,475 km ² to 1,247,689 km ² ) before the turn of the century. These distributional niche changes coincide with a northern latitude limit reaching as far as ~48° N by 2040, ~50° N by 2070, and ~52° N by 2100. These findings highlight the invasive potential of I. scapularis , with implications for public health and changing ecosystem dynamics.