The history of Diptera research at the Canadian National Collection of Insects is briefly outlined. Short biographic sketches of the coordinators of the Manual of Nearctic Diptera are given and the development of the Manual project is presented to provide background on their achievements. Lists of publications by each of the coordinators and of patronyms honouring them are provided. This Festschrift honours the remarkable contributions of the coordinators, J. Frank McAlpine, Bobbie V. Peterson, Guy E. Shewell, Herbert J. Teskey, J. Richard Vockeroth, and D. Monty Wood.

Efferia okanagana sp. nov. is described from specimens collected in the grasslands of the southern Interior of British Columbia, Canada, mainly the Okanagan Valley. The male and female genitalia are described and illustrated. The existing key to species of Efferia Coquillett is modified to enable identification of male and female E. okanagana. The species belongs to the E. arida species group and perhaps is most closely related to E. arida (Williston) and E. pinali Wilcox. Efferia coulei Wilcox is the closest sympatric relative. Sequences of the cytochrome oxidase I gene (DNA barcode) for E. okanagana and E. coulei show distinct clusters for each species that are approximately 7.0% divergent (uncorrected p distance). Efferia okanagana has an early flight period (May and June) and lives in low-elevation grasslands dominated by bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) Á. Löve) (Poaceae), especially where the soil is gravelly. It is considered a potential species at risk by the Committee on the Status of Endangered Wildlife in Canada.

The unusual new Neotropical genus Exalla is described and illustrated, along with three new species, E. browni, E. macalpinei, and E. shewelli. A key to the species is provided. The species are known from wet montane rainforest habitats in Colombia and Ecuador at elevations above 1500m.

Simulium (Simulium) acrotrichum Rubtsov, a black fly from Central Asia, provides a platform for examining the evolutionary relationships of selected species groups in the subgenus Simulium Latreille. The female, male, pupa, and larva of S. acrotrichum are properly associated and morphologically redescribed and illustrated. The banding sequence of the larval polytene chromosomes is compared with that of the Simulium subgeneric standard, from which it differs by nearly 30 fixed rearrangements. Structural and chromosomal features indicate that S. acrotrichum is the sister species of S. flavidum Rubtsov. Simulium acrotrichum can be placed confidently in a group consisting of the S. malyschevi Dorogostaisky, Rubtsov, and Vlasenko and S. reptans (L.) groups, which are part of a larger clade that also includes the S. jenningsi Malloch group. This more inclusive clade is defined chromosomally by a minimum of four fixed inversions, compared with the standard map for the subgenus Simulium. All four inversions are uniquely derived relative to the two selected outgroups, Simulium (Psilozia) vittatum Zetterstedt and Simulium (Boophthora) erythrocephalum (De Geer). The independent monophyly of the S. malyschevi and S. reptans groups, however, cannot be tested without study of additional group members. The problems illustrated by the taxonomic identity and phylogenetic placement of S. acrotrichum argue for an integrated approach to simuliid systematics, drawing from the character stores of morphology, cytology, and molecular biology.

The Nearctic species of the brachystomatid genus Heleodromia Haliday are revised. The following six species are recognized: Heleodromia boreoalpina Saigusa, H. chillcotti Sinclair sp. nov., H. cranehollowensis Cumming and Coovert sp. nov., H. irwini Wagner, H. pullata (Melander), and H. woodi Brooks sp. nov. The following new Palearctic distribution records are also reported: H. boreoalpina (Russian Far East), H. irwini (Germany, Russian Far East), and H. immaculata Haliday (Russian Far East). A key to adults, illustrations of male terminalia, and known distributions are included.

The Nearctic fauna of the genus Calamoncosis Enderlein is reviewed. Five species are present in eastern North America: C. carncrossi Nartshuk was recently described from New York; the Palearctic species C. aprica (Meigen) and C. glyceriae Nartshuk are newly recorded, and two new species, C. brooksi and C. munda, are described from eastern North America. A sixth species present in the Nearctic Region is represented by one female specimen and is not identifiable. Most Nearctic specimens were collected in peatlands or marshes in Quebec, but there are scattered records from other grass-dominated habitats in Ontario, Manitoba, New York, and Texas. A key to the described species of Calamoncosis in the Nearctic Region is given.

Medetera Fischer von Waldheim is the most speciose genus in the Medeterinae, with a nearly ubiquitous global distribution. Phylogenetic relationships within Medetera and between Medetera and four other medeterine genera were investigated using mitochondrial (COI, 16S) and nuclear (18S) markers to test morphological hypotheses. Our results confirm most of Bickel's hypotheses. Thrypticus Gerstäcker shows a sister-group relationship with Medetera + Dolichophorus Lichtwardt. The Medetera species included here split into two clades. One clade corresponds to the M. diadema L. – veles Loew species group sensu Bickel. The second clade is largely composed of the M. apicalis (Zetterstedt) species group sensu Bickel and the M. aberrans Wheeler species group sensu Bickel + Dolichophorus. Although most Medeterinae are associated with plants (mainly trees), species in at least two separate lineages demonstrate a secondary return to terrestrial habitats. The implication of this evolutionary phenomenon is briefly discussed.

Parerigone flavipes sp. nov. is described from Nepal. Morphological characteristics of the genus are discussed, especially with respect to the male and female terminalia. A key to the known species is provided.

A third Neotropical species of the genus Docosia Winnertz is described from the Colombian Andes. Three males and four females of D. adusta sp. nov. from Cundinamarca, Colombia, collected at 3600m elevation were examined. Detailed illustrations of the male and female terminalia are presented and morphological differences in relation to those of other species of the genus are discussed. The relationships between Holarctic and Neotropical species within Docosia are discussed and overlap of circumantarctic, tropical, and Nearctic elements in the northern Andes is considered.

The taxonomic status of the nine species of the mostly Neotropical genus Macrocerides Borgmeier is reviewed after the holotypes of seven species are examined. Macrocerides anacleti Borgmeier, M. brevicornis Borgmeier, and M. luteus Borgmeier are transferred to Myriophora Brown (new combinations). Macrocerides neivai Borgmeier is transferred to Apocephalus (new combination), creating a homonym with Apocephalus neivai Borgmeier for which the replacement name A. elizaldae is proposed. The African Macrocerides leydheckeri Schmitz is placed in a new genus, Macrocerophora. Tauricornus, a new subgenus of Macrocerides, is proposed for a monophyletic group that includes M. (T.) abaristalis Borgmeier, M. (T). attophilus Disney, and two new species, M. (T.) taurocephalus from southern Texas, United States of America, and M. (T.) borkenti from Costa Rica to northern South America.

Seventeen new species of Chrysopilus Macquart are described from New Caledonia with illustrations of the male head, wing, and genitalia. The new species are C. bicoloratus sp. nov., C. brunneabdominalis sp. nov., C. caliginosus sp. nov., C. chazeaui sp. nov., C. everti sp. nov., C. irwini sp. nov., C. frankmcalpinei sp. nov., C. mandjelia sp. nov., C. melinus sp. nov., C. noumea sp. nov., C. petersoni sp. nov., C. plautifrons sp. nov., C. sarramea sp. nov., C. shewelli sp. nov., C. teskeyi sp. nov., C. vockerothi sp. nov., and C. woodi sp. nov. Keys are provided to identify the species from New Caledonia.