The Microphorella chiragra species group is revised and includes M. chiragra Melander, M. longitarsis Melander and M. ornatipes Melander, plus the following 17 newly described species: M. barda sp. nov., M. bicristata sp. nov., M. bradleyisp. nov., M. dilatasp. nov., M. discretasp. nov., M. enigma sp. nov., M. megapternasp. nov., M. obscura sp. nov., M. paraplatypeza sp. nov., M. patrickensis sp. nov., M. platypeza sp. nov., M. sasquatchi sp. nov., M. setosa sp. nov., M. shorthouseisp. nov., M. tubulasp. nov., M. virgata sp. nov. and M. wilderaesp. nov. The species group occurs in the western Nearctic Region from Washington, Idaho and western Montana south through Oregon and California. The distribution of each species is mapped and a key to males is provided. COI mitochondrial DNA barcode analyses indicate the possible existence of additional cryptic species, and/or high intra-specific DNA barcode variation.

It has recently come to our attention that the name Empis (Enoplempis) occidentalis Sinclair, Brooks & Cumming (2025: 16) (Diptera: Empididae) is a junior primary homonym of Empis occidentalis Daugeron & Plant (in Daugeron et al. 2009: 645). The junior primary homonym is an invalid name according to Article 57.2 of the International Code of Zoological Nomenclature (ICZN, 1999) and Empis (Enoplempis) neoccidentalis nom. nov. is here proposed as a replacement name as required by Article 60.3 (ICZN, 1999) of the Code. The new specific name is a combination of neo for new and We thank Zachary Dankowicz (Washington, DC) who alerted us to the existence of the senior homonym and Jim O'Hara (Canadian National Collection of Insects, Ottawa) who reviewed an earlier draft of this publication.

The species of the Empis subgenus Enoplempis Bigot from western North America, including the Rocky Mountains westward, are revised. A total of 75 species are recorded from this region, including 54 new species. The western species are classified into 12 species groups as follows: the Empis (En.) arrecta species group-E. (En.) arrecta sp. nov., E. (En.) diokra sp. nov., E. (En.) occidentalis sp. nov., E. (En.) shoshona sp. nov.; the Empis (En.) bigoti species group-E. (En.) aerobatica Melander, E. (En.) bigoti Melander, E. (En.) collinsi sp. nov., E. (En.) montgomeryi sp. nov., E. (En.) multifaria sp. nov., E. (En.) paraerobatica sp. nov., E. (En.) podagra Melander; the Empis (En.) canaster species group-E. (En.) arizonensis sp. nov., E. (En.) canaster Melander, E. (En.) chillcotti sp. nov., E. (En.) contrasta sp. nov., E. (En.) falcata Melander, E. (En.) fitzgeraldi sp. nov., E. (En.) safra sp. nov., E. (En.) sagehenensis sp. nov., E. (En.) spokanensis sp. nov., E. (En.) subcanaster sp. nov.; the Empis (En.) clava species group-E. (En.) clava sp. nov., E. (En.) mariposa sp. nov., E. (En.) tularensis sp. nov.; the Empis (En.) delumbis species group-E. (En.) delumbis Melander, E. (En.) floricola sp. nov., E. (En.) sphaera sp. nov., E. (En.) spiculata sp. nov., E. (En.) tripenicillata sp. nov.; the Empis (En.) geneatis species group-E. (En.) fisheri sp. nov., E. (En.) geneatis (Melander), E. (En.) oharai sp. nov., E. (En.) subgeneatis sp. nov.; the Empis (En.) manca species group-E. (En.) bova sp. nov., E. (En.) manca Coquillett, E. (En.) submanca sp. nov., E. (En.) wilderae sp. nov.; the Empis (En.) mira species group-E. (En.) macdonaldi Sinclair, Brooks & Cumming, E. (En.) mira (Bigot), E. (En.) submira Sinclair, Brooks & Cumming, E. (En.) williamturneri Sinclair, Brooks & Cumming, E. (En.) winkleri Sinclair, Brooks & Cumming; the Empis (En.) nodipoplitea species group-E. (En.) nodipoplitea Steyskal; the Empis (En.) teres species group-E. (En.) scotti sp. nov., E. (En.) scutica sp. nov., E. (En.) teres Melander, E. (En.) undulasetosa sp. nov.; the Empis (En.) turgida species group-E. (En.) turgida sp. nov., E. (En.) woodleyi sp. nov.; and the Empis (En.) valentis species group-E. (En.) aeripes Melander, E. (En.) disconvenita Melander, E. (En.) dolabraria Melander stat. rev., E. (En.) flavobulla sp. nov., E. (En.) fresno sp. nov., E. (En.) mixopolia Melander, E. (En.) paraeripes sp. nov., E. (En.) subaeripes sp. nov., E. (En.) valentis Coquillett. Additionally, the following 17 western species are unplaced to species group: E. (En.) aphela sp. nov., E. (En.) blodgettensis sp. nov., E. (En.) californica sp. nov., E. (En.) cerina sp. nov., E. (En.) culcitella sp. nov., E. (En.) delnortensis sp. nov., E. (En.) dubitata sp. nov., E. (En.) genista sp. nov., E. (En.) holoptica sp. nov., E. (En.) manning sp. nov., E. (En.) missoula sp. nov., E. (En.) oregonensis sp. nov., E. (En.) poplitea Loew, E. (En.) richardvockerothi sp. nov., E. (En.) sierraensis sp. nov., E. (En.) susanae sp. nov., E. (En.) yakimensis sp. nov. The following new synonymy is designated: E. (En.) bullifera Kessel & Kessel = E. (En.) bigoti. Lectotypes are designated for the following species: E. (En.) aeripes, E. (En.) disconvenita, E. (En.) dolabraria, E. (En.) mixopolia, E. (En.) aerobatica, E. (En.) podagra, E. (En.) canaster, E. (En.) falcata, E. (En.) delumbis, E. (En.) manca, E. (En.) teres and E. (En.) poplitea. A key to all the western species is presented with distributions illustrated. The form of nuptial gift presentation displayed within this group, including the use of balloons (with or without prey) and unwrapped prey is indicated for species when known. In addition, new eastern records are listed and two new species from eastern North America are described (E. (En.) deceptiva sp. nov. and E. (En.) joanae sp. nov.). A complete list of all known species and species groups in the subgenus Enoplempis is also provided.

The Microphorella acroptera species group is revised and the Microphorella arcana species group is established. The M. acroptera species group includes M. acroptera Melander and M. tubifera Melander, plus the following 14 newly described species: M. acuminata sp. nov., M. bifida sp. nov., M. compacta sp. nov., M. convoluta sp. nov., M. cornuta sp. nov., M. elongata sp. nov., M. maculata sp. nov., M. paracroptera sp. nov., M. serpentina sp. nov., M. sinuosa sp. nov., M. subacroptera sp. nov., M. tenuis sp. nov., M. triangulata sp. nov. and M. trochanterata sp. nov. Four distinct lineages within the M. acroptera species group are recognized. The M. arcana species group includes the following three newly described species: M. arcana sp. nov., M. gilaensis sp. nov. and M. ovata sp. nov. Both species groups occur only in the western Nearctic Region. The M. acroptera species group is recorded from southeastern Alberta south to Washington, western Oregon and southern California, east to Nevada and northwestern Arizona. The M. arcana species group is known from California and central Arizona. The distribution of each species is mapped and a key to males of both species groups is provided, including an update to the Nearctic Microphorella species group key published by Cumming & Brooks (2022).

Churchill, Manitoba, Canada is a diverse Subarctic region that has been the focus of DNA barcoding efforts and research for decades. Despite this effort, there are still taxa in this region that are underrepresented in public databases, particularly hyperdiverse insect groups. We present a collaborative large-scale DNA barcode reference library for Diptera based on molecular data and expert taxonomic identification. The reference library contains 16786 specimens sampled around Churchill from 2005 to 2011. Specimens were identified by morphological means, sequenced for the animal barcode marker, and sorted into 2235 Molecular Operational Taxonomic Units (using Barcode Index Numbers: BINs) representing 68 families and 1211 named species. Eighty-four species shared a BIN with another species, 98 species were split across several BINs, and 1028 species were assigned to a unique BIN. The intraspecific and nearest neighbour distances varied across families, but most species can be easily distinguished from their nearest neighbours. By combining molecular data with taxonomic expertise, the barcode library provides species-level information for 12612 specimens, supplying future researchers with detailed taxonomic information and the opportunity to perform barcode-based specimen identifications for large-scale studies through sequence matching. Comparison of the Diptera composition of Churchill to other geographic regions reflected likely postglacial colonization northwards as well as a Beringian component. This study provides a publicly available, detailed reference library for use in future research, as well as new insights into the current diversity of Diptera present among the diverse habitats in this Subarctic region.### Competing Interest StatementThe authors have declared no competing interest.

Two new species of Microphorella Becker are described and illustrated from Chile and South Africa, respectively: M. amorimi sp. nov. (Maule Region) and M. irwini sp. nov. (Western Cape Province), representing the first formal records of the genus from the Neotropical and Afrotropical Regions. In addition, a key to the genera of Parathalassiinae and species of Microphorella from the Southern Hemisphere is also provided.

The Microphorella breviradia species group is established for three new species from western North America, namely Microphorella breviradia sp. nov., M. macdonaldi sp. nov. and M. vespera sp. nov., including an identification key to species. COI mitochondrial DNA barcode sequences were obtained for two of the three species and possibly suggest the existence of additional cryptic species. The phylogenetic relationships of the Microphorella breviradia species group to the remainder of the Microphorella species groups are reviewed on a worldwide basis. A key to the four known Nearctic species groups of Microphorella is also provided.

One species of Chimerothalassius Shamshev & Grootaert, namely C. marshalli sp. nov. is described from New Zealand, and two other species, namely C. riparius sp. nov. and C. sinclairi sp. nov. are described from New Caledonia. Two species of Microphorella Becker, namely M. bungle sp. nov. and M. viticula sp. nov., are described from Australia. These new parathalassiine descriptions increase the Australasian species diversity of Chimerothalassius and Microphorella to four species each. In addition, the genus Eothalassius Shamshev & Grootaert is recorded from New Caledonia based on a single female, and the male genitalia of the Australian species M. iota Colless is newly illustrated. A key to the genera and species of male Parathalassiinae in the Australasian Region is also provided.

The Nearctic species of the dolichopodid subfamily Microphorinae are revised. Two genera and 33 species are recognized including five species of Microphor Macquart and 28 species of Schistostoma Becker. Both genera are redefined, redescribed and diagnosed, a key to the genera and species in the Nearctic Region is provided, the known geographical distribution of each species is mapped and ecological information is summarized. In addition to the three previously known species of Nearctic Schistostoma, i.e., S. armipes (Melander), S. sycophantor (Melander) and S. yakimense (Melander), the Nearctic fauna includes eight species newly transferred from Microphor as well as 17 new species. These species of Schistostoma are classified into four species groups as follows: the S. atratum species group including S. atratum (Coquillett, 1900) comb. nov., S. borkenti sp. nov., S. chloeae sp. nov. and S. lillyae sp. nov.; the S. isommatum species group including S. caroleae sp. nov., S. evisceratum (Melander, 1940b) comb. nov., S. fitzgeraldi sp. nov., S. isommatum (Melander, 1928) comb. nov., S. powelli sp. nov., S. shamshevi sp. nov., S. sinclairi sp. nov., S. susanae sp. nov. and S. tacomae (Melander, 1940b) comb. nov.; the S. ravidum species group including S. armipes (Melander, 1928), S. arnaudi sp. nov., S. cirripes (Melander, 1940b) comb. nov., S. heatherae sp. nov., S. longistylum sp. nov., S. michaeli sp. nov., S. oharai sp. nov., S. ravidum (Coquillett, 1895) comb. nov., S. robustum (Melander, 1928) comb. nov., S. rudei sp. nov., S. strigilifer (Melander, 1940b) comb. nov. and S. sycophantor (Melander, 1902); and the S. yakimense species group including S. pecki sp. nov., S. runyoni sp. nov. and S. yakimense (Melander, 1928). Schistostoma ravum (Melander, 1940b) comb. nov. is also transferred from Microphor and is newly synonymized with S. evisceratum (Melander, 1940b), syn. nov. The Nearctic members of Microphor now comprise only three of the previously known species, plus two new species. These five species are classified into two species groups as follows: the M. discalis species group including M. discalis Melander, 1940b, M. skevingtoni sp. nov. and M. turneri sp. nov.; and the M. obscurus species group including M. bilineatus (Melander, 1902) and M. obscurus Coquillett, 1903. Lectotype designations are made for Holoclera bilineata Melander, Microphorus armipes Melander, Microphorus ravidus Coquillett, Microphorus strigilifer Melander and Holoclera sycophantor Melander.

The Empis (Enoplempis) mira species group is revised and includes the type species of Enoplempis and four new species (E. macdonaldi sp. nov., E. submira sp. nov., E. williamturneri sp. nov., E. winkleri sp. nov.). A lectotype is designated for Enoplempis mira Bigot. The species group is defined by the yellow body colour, directionally asymmetrical male hindlegs and geniculate hindlegs in both males and females. The group has not been found outside of western North America and is known from California, Oregon, Idaho and Washington.

The Nearctic genus Philetus Melander, 1928 is a rarely collected group of empidid flies that contains two western species, namely P. memorandus Melander and P. schizophorus Melander. The genus was fully diagnosed by Cumming et al. (2016) with both known species redescribed and their distributions mapped. Here we describe a third species of Philetus from a single male collected recently in the Richardson Mountains of the Yukon Territory in Canada and provide a key to species based on male morphology. Terms used for adult structures follow those of Cumming & Wood (2017) and methods follow those outlined in Cumming et al. (2016).

The Holarctic genus Gloma Meigen is revised and includes five species (G. fuscipennis Meigen, G. fuscipes Melander, G. luctuosa Melander, G. pectinipes Melander, G. pyricornis Saigusa Sinclair sp. nov.) and two undescribed species from China, presently known only from females. The monotypic Baltic amber genus Palaeoparamesia Meunier is discussed as possibly congeneric with Gloma. The Baltic amber species Gloma hirta Loew is considered a nomen dubium. A lectotype is designated for Gloma luctuosa. All species are described or diagnosed, and their geographic distributions mapped. A World key to the species of Gloma is provided. Phylogenetic placement of the genus, including a possible new relationship with Oreogeton Schiner is considered, and the relationships and zoogeographic history of the species are discussed based on a morphological cladistic analysis.

Phylogenetic relationships of the subgroups of Parathalassiinae are presented, based on a morphological cladistic analysis. Worldwide, all known extant genera, species groups and newly discovered undescribed lineages are represented in the analysis. Some previously proposed generic relationships are supported by the analysis, but recognition of many current genera renders the present concept of Microphorella Becker as both paraphyletic and polyphyletic. Microphorella merzi Gatt is here classified in Eothalassius Shamshev Grootaert, as Eothalassius merzi (Gatt) comb. nov. A preliminary classification with all included extant lineages within the Parathalassiinae (at the genus and species group level) is outlined. The ranking of these lineages is discussed and several species groups of Microphorella may need to be elevated to generic or subgeneric level, whereas some currently recognized genera may need to be relegated to subgenera.

Two closely related and distinctive species of Schistostoma Becker, i.e. Schistostoma burmanicum sp. nov. and Schistostoma foliatum sp. nov., are described from two male specimens preserved in mid-Cretaceous Burmese amber and recorded as the first known fossil representatives of this extant genus of Microphorinae. Both species possess greatly enlarged lamellate fore tibiae and modified leg chaetotaxy that are presumably male secondary sexual features. The generic limits of Schistostoma are briefly discussed and a rationale for the inclusion of these new species is provided.

Study of all flies (Diptera) collected for one year from a four-hectare (150 x 266 meter) patch of cloud forest at 1,600 meters above sea level at Zurquí de Moravia, San José Province, Costa Rica (hereafter referred to as Zurquí), revealed an astounding 4,332 species. This amounts to more than half the number of named species of flies for all of Central America. Specimens were collected with two Malaise traps running continuously and with a wide array of supplementary collecting methods for three days of each month. All morphospecies from all 73 families recorded were fully curated by technicians before submission to an international team of 59 taxonomic experts for identification.        Overall, a Malaise trap on the forest edge captured 1,988 species or 51% of all collected dipteran taxa (other than of Phoridae, subsampled only from this and one other Malaise trap). A Malaise trap in the forest sampled 906 species. Of other sampling methods, the combination of four other Malaise traps and an intercept trap, aerial/hand collecting, 10 emergence traps, and four CDC light traps added the greatest number of species to our inventory. This complement of sampling methods was an effective combination for retrieving substantial numbers of species of Diptera. Comparison of select sampling methods (considering 3,487 species of non-phorid Diptera) provided further details regarding how many species were sampled by various methods.        Comparison of species numbers from each of two permanent Malaise traps from Zurquí with those of single Malaise traps at each of Tapantí and Las Alturas, 40 and 180 km distant from Zurquí respectively, suggested significant species turnover. Comparison of the greater number of species collected in all traps from Zurquí did not markedly change the degree of similarity between the three sites, although the actual number of species shared did increase.        Comparisons of the total number of named and unnamed species of Diptera from four hectares at Zurquí is equivalent to 51% of all flies named from Central America, greater than all the named fly fauna of Colombia, equivalent to 14% of named Neotropical species and equal to about 2.7% of all named Diptera worldwide. Clearly the number of species of Diptera in tropical regions has been severely underestimated and the actual number may surpass the number of species of Coleoptera.        Various published extrapolations from limited data to estimate total numbers of species of larger taxonomic categories (e.g., Hexapoda, Arthropoda, Eukaryota, etc.) are highly questionable, and certainly will remain uncertain until we have more exhaustive surveys of all and diverse taxa (like Diptera) from multiple tropical sites.        Morphological characterization of species in inventories provides identifications placed in the context of taxonomy, phylogeny, form, and ecology. DNA barcoding species is a valuable tool to estimate species numbers but used alone fails to provide a broader context for the species identified.

Chimerothalassius runyoni sp. nov. is described from rocky coastlines of Montserrat and Dominica, and the genus is newly recorded from the Pacific coast of Costa Rica, based on female specimens of an undescribed species.

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.

Cheiromyia carolina Limeira-de-Oliveira & Brooks sp. nov. and C. nordestina Limeira-de-Oliveira & Cumming sp. nov. are described from Brazil, and C. fuscipennis Pollet & Brooks sp. nov. is described from the Mitaraka Mountains in southwestern French Guiana. New distribution records are reported for C. brevitarsis Brooks, C. palmaticornis (Parent) and C. pennaticornis (Parent), and a revised key to males of the eight known species of Cheiromyia Dyte, 1980 is provided. The female of C. pennaticornis is also described for the first time.

A large diversity of saproxylic Empidoidea from a temperate deciduous forest in southern Quebec is documented. Adults of 43 empidoid species representing 19 genera in 12 subfamilies and three families were collected from in situ sealed emergence traps placed over decayed logs of American beech (Fagus grandifolia Ehrhart) and sugar maple (Acer saccharum Marshall). The results of this technique give a clear indication of the saproxylic larval and pupal habitat of these species. The importance of Empidoidea as larval predators in decayed wood niches is noted.