A cladistic analysis of the Empidoidea and basal lineages of the Cyclorrhapha, based on morphological characters, confirms the monophyly of both groups as well as that of the                    Eremoneura. The resulting final trees are used to revise the classification of the Empidoidea to include the following five families: Empididae, Hybotidae, Atelestidae (including Nemedininae n. subfam.), Brachystomatidae rev. stat. (comprising the subfamilies Brachystomatinae, Ceratomerinae and Trichopezinae), and Dolichopodidae s.lat. The family Microphoridae is not recognized, and the Microphorinae and Parathalassiinae are assigned to the Dolichopodidae s.lat. The Dolichopodidae s.str. includes 15 subfamilies that were previously recognized within the family. Within the Empidoidea we found support for Atelestidae as the sister group to the Hybotidae and for the monophyly of Parathalassiinae + Dolichopodidae s.str. The Empididae remains poorly defined and the genera Homalocnemis Philippi, Iteaphila Zetterstedt, Anthepiscopus Becker, and Oreogeton Schiner are classified as incertae sedis within the                   Empidoidea. In addition, the following higher taxa are proposed: Symballophthalmini n. tribe, Bicellariini n. tribe, Oedaleinae rev. stat., and Trichininae rev. stat., which are all assigned to the Hybotidae. The genus Sematopoda Collin is tentatively assigned to Trichopezinae, and Xanthodromia Saigusa is transferred from Hemerodromiinae to Brachystomatinae.        All morphological characters are extensively discussed and illustrated, including details of the antennae, mouthparts, internal thoracic structures, wings, and male and female terminalia. In addition, a key to families and unplaced genus groups of the Empidoidea is provided. Feeding habits are also discussed in terms of the empidoid ground plan condition.

Courtship displays of empidine dance flies (Diptera: Empididae), which include transfers of nuptial gifts during mating, are reviewed in light of sexual selection theory. Sex-role reversed courtship behavior, involving female swarming and male choice, appears to be correlated with certain female secondary sexual characters that are widespread throughout the Empidinae. The tendency to shift mate choice from females to males, and the apparent development of autogeny in many empidine species, are both hypothesized to have resulted from males monopolizing the proteinaceous food source of non-hunting females, through transfers of nuptial gifts of prey. The autogenous condition appears to have led to the ritualized presentation of various types of inedible nuptial gifts by males of several species, possibly including the development of secreted nuptial gifts, or balloons, as displays of male fitness.

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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.