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'Insect Biodiversity' brings together leading scientific experts to assess the impact insects have on humankind and the Earth's fragile ecosystems. It examines why insect biodiversity matters and how the rapid evolution of insect species is affecting us all.

More than any other group of macro-organisms, true flies (Diptera) dominate the freshwater environment. Nearly one-third of all flies—roughly 46,000 species—have some developmental connection with an aquatic environment. Their abundance, ubiquity, and diversity of adaptations to the aquatic environment position them as major drivers of ecosystem processes and as sources of products and bioinspiration for the benefit of human society. Larval flies are well represented as ecosystem engineers and keystone species that alter the abiotic and biotic environments through activities such as burrowing, grazing, suspension feeding, and predation. The enormous populations sometimes achieved by aquatic flies can provide the sole or major dietary component for other organisms. Harnessing the services of aquatic Diptera for human benefit depends on the ingenuity of the scientific community. Aquatic flies have played a role as indicators of water quality from the earliest years of bioassessment. They serve as indicators of historical and future ecological and climate change. As predators and herbivores, they can serve as biological control agents. The association of flies with animal carcasses in aquatic environments provides an additional set of tools for forensic science. The extremophilic attributes of numerous species of Diptera offer solutions for human adaptation to harsh terrestrial and extraterrestrial environments. The potential pharmaceutical and industrial applications of the symbiotic microbial community in extremophilic Diptera are better explored than are those of dipteran chemistry. Many flies provide valuable ecological and human services as aquatic immatures, but are also pests and vectors of disease agents as terrestrial adults. The scientific community, thus, is challenged with balancing the benefits and costs of aquatic Diptera, while maintaining sustainable populations as more species face extinction.

'Insect Biodiversity' brings together leading scientific experts to assess the impact insects have on humankind and the Earth's fragile ecosystems. It examines why insect biodiversity matters and how the rapid evolution of insect species is affecting us all.

The family Simuliidae includes more than 2000 species of black flies worldwide. Their morphological uniformity creates difficulty for species identification, which limits our knowledge of their ecology and vectorial role. We investigated the systematics of black flies in a semi-arid area of the Iberian Peninsula, an ecologically harsh environment for these organisms. Sampling adult black flies in three different habitats (by means of CDC traps) and in avian nest boxes and collecting immature stages in high-salinity rills provided a representative sample of the component species. A combination of approaches, including morphological, chromosomal, and molecular (based on the mitochondrial cytochrome C oxidase subunit I (COI) and internal transcribed spacer 2 (ITS2) genes) revealed five species: four common species ( Simulium intermedium , S . petricolum , S . pseudequinum , and S . rubzovianum ) and the first European record for S . mellah . Barcoding gap and phylogenetic analyses revealed that ITS2 is a key marker to identify the species, whereas the COI marker does not provide enough resolution to identify some species or infer their phylogenetic relationships. Morphological and chromosomal features are also provided to identify S . mellah unequivocally. Our study highlights the need for integrated studies of black flies in ecologically extreme habitats to increase our knowledge of their distribution, ecology, and potential risks for public health.

The ability of aquatic insects to colonize Earth's most remote freshwater habitats, such as those of islands and deserts, is limited to select taxa. Among black flies, the premiere colonization specialist is Simulium ruficorne Macquart, the only species known from both the Afrotropical and Palearctic regions. We investigated the cytogenetics of S. ruficorne to gain insight into its wide geographic distribution and ability to colonize oceanic islands and deserts. On the basis of larval polytene chromosomes from 14 locations, we documented 17 novel and previously known chromosomal rearrangements and established five cytoforms (A1, A2, B, C, and D), of which probably four (A1/A2, B, C, and D) are distinct species and two (A1 and A2) represent sex-chromosome polymorphism involving a heteroband in the long arm of chromosome III. The chromosome restructuring phenomena associated with the five cytoforms are consistent with the trend in the Simuliidae that one and the same rearrangement can assume different functions in the various descendants of a common ancestor in which the rearrangement was polymorphic. The most widely distributed cytoforms are A1 and A2, which are found in North Africa, the Canary Islands, and Majorca. Simulium ruficorne, the only known black fly in the Hoggar Mountains of the central Sahara Desert, represents a cohesive population of cytoform A1 little differentiated from other North African populations of A1 and A2. Cytoform B inhabits the West African mainland, cytoform C is on Tenerife, and cytoform D is on Cape Verde. We suggest that dispersal and colonization specialists, such as S. ruficorne, are multivoltine inhabitants of temporary streams, and must relocate as their habitats deteriorate. Simulium ruficorne, therefore, should have adaptations that contribute to successful dispersal and colonization, perhaps largely physiological in nature, such as tolerance of high temperatures and droughts.

Black flies are blood-sucking insects of public health importance, and they are effective vectors of pathogens and parasites, such as filarial nematodes of the genus Onchocerca . Our previous surveys have shown that individuals of Simulium turgaicum are annoying pests of humans and livestock in the Aras River Basin of Iran. In the present study, adult black flies of S. turgaicum were trapped from different ecotopes of five villages in Khoda-Afarin County, Iran. By using a sensitive nested PCR assay and targeting the nuclear 18S rDNA-ITS1 marker, filarial infections were found in 38 (1.89%) of 2005 black flies. Homology exploration of 360 bp of the sequences indicated that the filarial worms are members of the family Onchocercidae, with maximum alignment scores of 93–95%. Phylogenetic analysis showed that two Iranian Onchocerca isolates were clustered in the O. fasciata – O. volvulus lineage and were well separated from other filarial nematodes. Both the entomological evidence (empty abdomen of the specimens) and climatologic data (adequate accumulated degree days for development) suggest that the filarial DNA was probably that of infective larvae of vertebrates. This is the first report of an infection by Onchocerca species in S. turgaicum and the first record of onchocercids in black flies in Iran; however, more research is required to demonstrate transmission of these filarial worms by black flies in nature.

The European black fly Simulium (Simulium) colombaschense (Scopoli), once responsible for as many as 22,000 livestock deaths per year, is chromosomally mapped, permitting its evolutionary relationships and pest drivers to be inferred. The species is 12 fixed inversions removed from the standard sequence of the subgenus Simulium. Three of these fixed inversions, 38 autosomal polymorphisms, and a complex set of 12 X and 6 Y chromosomes in 29 zygotic combinations uniquely characterize S. colombaschense and reveal 5 cytoforms: 'A' in the Danube watershed, 'B' in Italy's Adige River, 'C' in the Aliakmonas River of Greece, 'D' in the Aoös drainage in Greece, and 'E' in the Belá River of Slovakia. 'C' and 'D' are reproductively isolated from one another, and 'B' is considered a cytotype of 'A,' the probable name bearer of colombaschense. The species status of 'E' cannot be determined without additional collections. Three derived polytene sequences, based on outgroup comparisons, place S. colombaschense in a clade of species composed of the S. jenningsi, S. malyschevi, and S. reptans species groups. Only cytoforms 'A' and 'B' are pests. Within the Simuliidae, pest status is reached through one of two principal pathways, both of which promote the production of large populations of blood-seeking flies: (1) colonization of the world's largest rivers (habitat specialization) or (2) colonization of multiple habitat types (habitat generalization). Evolutionary acquisition of the ability to colonize large rivers by an ancestor of the S. jenningsi-malyschevi-reptans clade set the scene for the pest status of S. colombaschense and other big-river members of the clade. In an ironic twist, the macrogenome of S. colombaschense reveals that the name associated with history's worst simuliid pest represents a complex of species, two or more of which are nonpests potentially vulnerable to loss of their limited habitat.

Background Leucocytozoonosis, a parasitic disease of birds, is caused by haemosporidian protozoan parasites of the genus Leucocytozoon , which infect diverse avian species, including poultry. These parasites are transmitted by several black fly species, but knowledge of the factors determining the diversity and prevalence in these vectors, which is crucial for fully understanding disease epidemiology, is largely unexplored. In this study, we investigated factors associated with the prevalence and diversity of Leucocytozoon species in black flies from Thailand. Methods Adults of two black fly taxa ( Simulium asakoae Takaoka and Davies complex and S. khelangense Takaoka, Srisuka and Saeung) were collected using sweep nets at nine locations in northern and northeastern regions of Thailand. Specimens were identified morphologically and the results corroborated by DNA barcoding. Molecular methods using specific primers for amplification of the mitochondrial cytochrome b (cyt b ) gene of Leucocytozoon were used to detect the parasite in black flies. Species and lineages of Leucocytozoon were determined using the MalAvi database of malaria parasites and related haemosporidians in avian hosts. Regression analysis was used to examine relationships between Leucocytozoon diversity and prevalence, black fly abundance and habitat characteristics. Results A total of 11,718 adult black flies were collected, of which 4367 were members of the S. asakoae complex and 7351 were S. khelangense . For molecular detection of Leucocytozoon , we randomly selected 300 individual female black flies of the S . asakoae complex and 850 females of S . khelangense pooled into groups of five individuals (= 170 pools). A total of 34 of the 300 specimens of the S. asakoae complex and 118 of the 170 pools of S . khelangense were positive for Leucocytozoon . Fifty-four lineages (haplotypes) were identified, all of which belonged to those reported in domestic chickens, Gallus gallus , with one exception that was identified in S. khelangense and found to be closely related to the Leucocytozoon lineages reported in owls; this is the first record of the latter lineage in Asian black flies. Among these haplotypes, nine and 45 were exclusively found in the S. asakoae complex and S. khelangense , respectively. No lineage was shared between these black fly taxa. Analysis of similarity (ANOSIM) revealed significant Leucocytozoon lineage composition between the two black flies. Phylogenetic analysis found that Leucocytozoon lineages in the S. asakoae complex and S. khelangense are largely isolated, agreeing with the ANOSIM result. The overall prevalence of Leucocytozoon in the S. asakoae complex was 11.3% and ranged from 9% to 13% in each collection. Leucocytozoon prevalence in S. khelangense was 21%, varying from 13% to 37% in each collection. The Shannon H′ index indicated greater Leucocytozoon diversity in S. khelangense (H′ = 3.044) than in the S. asakoae complex (H′ = 1.920). Regression analysis revealed that Leucocytozoon diversity was positively related to black fly abundance and negatively related to maximum air temperature. Conclusions The results of this study show that the prevalence and diversity of Leucocytozoon lineages in the S . asakoae complex and S. khelangense from Thailand were associated with the abundance of these black flies and with air temperature. The Leucocytozoon lineages identified also showed some degree of black fly taxon specificity, possibly related to different abundance peaks of these vectors. The environmental conditions that favor the development of black flies are possibly a driver of Leucocytozoon prevalence, diversity and vector–parasite co-evolution. Graphical Abstract

The increasing attention on Vietnam as a biodiversity hotspot prompted an investigation of the potential for cryptic diversity in black flies, a group well known elsewhere for its high frequency of isomorphic species. We analyzed the banding structure of the larval polytene chromosomes in the Simulium tuberosum species group to probe for diversity beyond the morphological level. Among 272 larvae, 88 different chromosomal rearrangements, primarily paracentric inversions, were discovered in addition to 25 already known in the basic sequences of the group in Asia. Chromosomal diversity in Vietnam far exceeds that known for the group in Thailand, with only about 5% of the rearrangements shared between the two countries. Fifteen cytoforms and nine morphoforms were revealed among six nominal species in Vietnam. Chromosomal evidence, combined with available molecular and morphological evidence, conservatively suggests that at least five of the cytoforms are valid species, two of which require formal names. The total chromosomal rearrangements and species (15) now known from the group in Vietnam far exceed those of any other area of comparable size in the world, supporting the country's status as a biodiversity hotspot. Phylogenetic inference based on uniquely shared, derived chromosomal rearrangements supports the clustering of cytoforms into two primary lineages, the Simulium tani complex and the Southeast Asian Simulium tuberosum subgroup. Some of these taxa could be threatened by habitat destruction, given their restricted geographical distributions and the expanding human population of Vietnam.

One of the most popular tools for species discovery and resolution is the DNA barcode, typically based on the cytochrome c oxidase I (COI) gene. However, other non-genic barcodes are available for Diptera. The banding sequence of polytene chromosomes in some dipteran cells, particularly of the larval silk glands, can provide a unique species barcode. We used the sequence of bands to reveal a new species of black fly in the Simulium (Boreosimulium) annulus species group from California, USA. To further characterize the species and provide more integrated taxonomy, we morphologically described all life stages above the egg, formally named the species Simulium ustulatum n. sp., and provided a conventional COI barcode. The COI barcode confirmed the chromosomal and morphological evidence that the species is a new member of the S. annulus group, and enabled identification of the larva and female, which are structurally similar to those of other species. The chromosomal barcode shows that this species has the most rearranged complement, compared with the eight other North American members of its species group, with up to 12 times the number of fixed rearrangements. Up to six chromosomal rearrangements, including autosomal polymorphisms and sex-linked phenomena, are shared with other members of the group. The most unique and conspicuous chromosomal feature of this new species is a large, pale-staining chromocenter from which the six chromosomal arms radiate. The distribution of this univoltine species in lowland rivers of California’s Central Valley could make it vulnerable, given climate change and increasing land development.