Latitudinal diversity of biting midge species within the Obsoletus group across three habitats in Europe

Habitat type and host grazing regimen influence the soil microbial diversity and communities within potential biting midge larval habitats

BACKGROUND

Biting midges (Culicoides spp.) are important vectors of diverse microbes such as viruses, protozoa, and nematodes that cause diseases in wild and domestic animals. However, little is known about the role of microbial communities in midge larval habitat utilization in the wild. In this study, we characterized microbial communities (bacterial, protistan, fungal and metazoan) in soils from disturbed (bison and cattle grazed) and undisturbed (non-grazed) pond and spring potential midge larval habitats. We evaluated the influence of habitat and grazing disturbance and their interaction on microbial communities, diversity, presence of midges, and soil properties.

RESULTS

Bacterial, protistan, fungal and metazoan community compositions were significantly influenced by habitat and grazing type. Irrespective of habitat and grazing type, soil communities were dominated by phyla Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria (Bacteria); Apicomplexa, Cercozoa, Ciliophora, Ochrophyta (Protists); Chytridiomycota, Cryptomycota (Fungi) and Nematoda, Arthropoda (Metazoa). The relative abundance of Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria, Verrucomicrobia (Bacteria); Apicomplexa, Lobosa (Protists); Ascomycota, Blastomycotina, Cryptomycota (Fungi); and Platyhelminthes (Metazoa) were significantly affected by grazing type. Of note, midge prevalence was higher in grazed sites (67-100%) than non-grazed (25%). Presence of midges in the soil was negatively correlated with bacterial, protistan, fungal and metazoan beta diversities and metazoan species richness but positively correlated with protistan and fungal species richness. Moreover, total carbon (TC), nitrogen (TN) and organic matter (OM) were negatively correlated with the presence of midges and relative abundances of unclassified Solirubrobacterales (Bacteria) and Chlamydomonadales (Protists) but positively with Proteobacteria and unclassified Burkholderiales (Bacteria).

CONCLUSIONS

Habitat and grazing type shaped the soil bacterial, protistan, fungal and metazoan communities, their compositions and diversities, as well as presence of midges. Soil properties (TN, TC, OM) also influenced soil microbial communities, diversities and the presence of midges. Prevalence of midges mainly in grazed sites indicates that midges prefer to breed and shelter in a habitat with abundant hosts, probably due to greater accessibility of food (blood meals). These results provide a first glimpse into the microbial communities, soil properties and prevalence of midges in suspected midge larval habitats at a protected natural prairie site.

Species Identity, Life History, and Geographic Distance Influence Gut Bacterial Communities in Lab-Reared and European Field-Collected Culicoides Biting midges

Bacteria are part of the insect gut system and influence many physiological traits of their host. Gut bacteria may even reduce or block the transmission of arboviruses in several species of arthropod vectors. Culicoides biting midges are important arboviral vectors of several livestock and wildlife diseases, yet limited information is available on their gut bacterial communities. Addressing this gap will help inform how these communities can be manipulated and ultimately used as novel tools to control pathogens. To assess how bacterial communities change during the life stages of lab-reared C. nubeculosus and C. sonorensis, endosymbiotic bacteria were identified using Illumina sequencing of 16S rRNA and taxonomically characterised. Analyses were conducted to determine how gut bacterial communities in adults are influenced by species identity and geographic distance among biting midge populations. Communities of the two lab-reared Culicoides species significantly changed after pupation and with maturation into 6-day-old adults. Pseudomonas, Burkholderiaceae and Leucobacter bacteria were part of a core community that was trans-stadially transmitted and found throughout their life cycle. Among field-collected biting midges, the bacterial communities were unique for almost each species. Cardinium, Rickettsia and Wolbachia were some of the most abundant bacteria in midges collected from wetlands. Only Pseudomonas was present in high relative abundance in all field-collected species. In this study, species identity, as well as geographic distance, influenced the gut bacterial communities and may partly explain known inter- and intra-species variability in vector competence. Additionally, stably associated bacterial species could be candidates for paratransgenic strategies to control vector-borne pathogens.

A Survey on Native and Invasive Mosquitoes and Other Biting Dipterans in Northern Spain

PURPOSE

Haematophagous Diptera, such as mosquitoes (Culicidae), biting midges (Ceratopogonidae), and black flies (Simuliidae), are important insects for public and animal health due to their capacity to bite and transmit pathogens. Outdoor recreation areas are usually affected by biting species and provide suitable habitats to both adult and immature stages. This study aimed to determine the species diversity and larval sites of these Diptera groups in two golf courses.

METHODS

A multi-method collection approach using ultraviolet-CDC traps, human landing catches, collection in breeding sites, and ovitraps was implemented during summer 2020 in northern Spain. Insects were determined by morphological features accompanied by DNA barcoding.

RESULTS

A total of ten native mosquito species were recorded either as adults or as larval stages. The invasive species Aedes japonicus was collected only at egg or pupa stage in ovitraps. Culex pipiens s.l. and Culex torrentium were both common mosquito species accounting for 47.9% of the total larval site collections and their larvae might be found in a wide range of natural and artificial sites. Culiseta longiareolata specimens were also prominent (30.1% of the total) and occurred exclusively in man-made water-filled containers. A total of 13 Culicoides species were identified, 10 of which were captured by ultraviolet-CDC traps, particularly members of the Obsoletus complex (Culicoides obsoletus/Culicoides scoticus, 74.9%) and seven species by emergence traps, being the two most abundant C. kibunensis (44.8%) and C. festivipennis (34.9%). Simulium cryophilum was also collected hovering around the operator under field sampling.

CONCLUSION

A comprehensive representation of the blood-sucking Diptera fauna and their larval sites was obtained by the multi-method approach in two Spanish golf courses.

The tree that hides the forest: cryptic diversity and phylogenetic relationships in the Palaearctic vector Obsoletus/Scoticus Complex (Diptera: Ceratopogonidae) at the European level

Background

Culicoides obsoletus is an abundant and widely distributed Holarctic biting midge species, involved in the transmission of bluetongue virus (BTV) and Schmallenberg virus (SBV) to wild and domestic ruminants. Females of this vector species are often reported jointly with two morphologically very close species, C. scoticus and C. montanus, forming the Obsoletus/Scoticus Complex. Recently, cryptic diversity within C. obsoletus was reported in geographically distant sites. Clear delineation of species and characterization of genetic variability is mandatory to revise their taxonomic status and assess the vector role of each taxonomic entity. Our objectives were to characterize and map the cryptic diversity within the Obsoletus/Scoticus Complex.

Methods

Portion of the cox1 mitochondrial gene of 3763 individuals belonging to the Obsoletus/Scoticus Complex was sequenced. Populations from 20 countries along a Palaearctic Mediterranean transect covering Scandinavia to Canary islands (North to South) and Canary islands to Turkey (West to East) were included. Genetic diversity based on cox1 barcoding was supported by 16S rDNA mitochondrial gene sequences and a gene coding for ribosomal 28S rDNA. Species delimitation using a multi-marker methodology was used to revise the current taxonomic scheme of the Obsoletus/Scoticus Complex.

Results

Our analysis showed the existence of three phylogenetic clades (C. obsoletus clade O2, C. obsoletus clade dark and one not yet named and identified) within C. obsoletus. These analyses also revealed two intra-specific clades within C. scoticus and raised questions about the taxonomic status of C. montanus.

Conclusions

To our knowledge, our study provides the first genetic characterization of the Obsoletus/Scoticus Complex on a large geographical scale and allows a revision of the current taxonomic classification for an important group of vector species of livestock viruses in the Palaearctic region.