Community analysis of the abundance and diversity of biting midge species (Diptera: Ceratopogonidae) in three European countries at different latitudes

Urbanization correlates with the prevalence and richness of blood parasites in Eurasian Blackbirds (Turdus merula)

Urbanization is increasing worldwide, producing severe environmental impacts. Biodiversity is affected by the expansion of cities, with many species being unable to cope with the different human-induced stressors present in these landscapes. However, this knowledge is mainly based on research from taxa such as plants or vertebrates, while other organisms like protozoa have been less studied in this context. The impact of urbanization on the transmission of vector-borne pathogens in wildlife is still unclear despite its relevance for animal and human health. Here, we investigated whether cities are associated with changes in the prevalence and richness of lineages of three vector-borne protozoans (Plasmodium, Haemoproteus and Leucocytozoon) in Eurasian blackbirds (Turdus merula) from multiple urban and forest areas in Europe. Our results show important species-specific differences between these two habitat types. We found a significant lower prevalence of Leucocytozoon in urban birds compared to forest birds, but no differences for Plasmodium and Haemoproteus. Furthermore, the richness of parasite lineages in European cities was higher for Plasmodium but lower for Leucocytozoon than in forests. We also found one Plasmodium lineage exclusively from cities while another of Leucocytozoon was only found in forests suggesting a certain level of habitat specialization for these protozoan vectors. Overall, our findings show that cities provide contrasting opportunities for the transmission of different vector-borne pathogens and generate new scenarios for the interactions between hosts, vectors and parasites.

Bird species with wider geographical ranges have higher blood parasite diversity but not prevalence across the African-Eurasian flyway

Avian blood parasites, from the genera Plasmodium, Haemoproteus and Leucocytozoon, are predicted to alter their range and prevalence as global temperatures change, and host and vector ranges shift. Understanding large-scale patterns in the prevalence and diversity of avian malaria and malaria-like parasites is important due to an incomplete understanding of their effects in the wild, where studies suggest even light parasitaemia can potentially cause rapid mortality, especially in naïve populations. We conducted phylogenetically controlled analyses to test for differences in prevalence and lineage diversity of haemoparasite infection (for Plasmodium, Haemoproteus and Leucocytozoon) in and between resident and migratory species along the African-Eurasian flyway. To test whether migratory strategy or range size drives differences in parasite prevalence and diversity between resident and migrant species, we included three categories of resident species: Eurasian only (n = 36 species), African only (n = 41), and species resident on both continents (n = 17), alongside intercontinental migrants (n = 64), using a subset of data from the MalAvi database comprising 27,861 individual birds. We found that species resident on both continents had a higher overall parasite diversity than all other categories. Eurasian residents had lower Plasmodium diversity than all other groups, and both migrants and species resident on both continents had higher Haemoproteus diversity than both African and Eurasian residents. Leucocytozoon diversity did not differ between groups. Prevalence patterns were less clear, with marked differences between genera. Both Plasmodium and Leucocytozoon prevalence was higher in species resident on both continents and African residents than in migrants and Eurasian residents. Haemoproteus prevalence was lower in Eurasian residents than species resident on both continents. Our findings contrast with previous findings in the North-South American flyway, where long-distance migrants had higher parasite diversity than residents and short-distance migrants, although we found contrasting patterns for parasite diversity to those seen for parasite prevalence. Crucially, our results suggest that geographic range may be more important than migratory strategy in driving parasite diversity within species along the African-Palaearctic flyway. Our findings differ between the three parasite genera included in our analysis, suggesting that vector ecology may be important in determining these large-scale patterns. Our results add to our understanding of global patterns in parasite diversity and abundance, and highlight the need to better understand the influence of vector ecology to understand the drivers of infection risk and predict responses to environmental change.

Host life-history traits predict haemosporidian parasite prevalence in tanagers (Aves: Thraupidae)

Vector-borne parasites are important ecological drivers influencing life-history evolution in birds by increasing host mortality or susceptibility to new diseases. Therefore, understanding why vulnerability to infection varies within a host clade is a crucial task for conservation biology and for understanding macroecological life-history patterns. Here, we studied the relationship of avian life-history traits and climate on the prevalence of Plasmodium and Parahaemoproteus parasites. We sampled 3569 individual birds belonging to 53 species of the family Thraupidae. Individuals were captured from 2007 to 2018 at 92 locations. We created 2 phylogenetic generalized least-squares models with Plasmodium and Parahaemoproteus prevalence as our response variables, and with the following predictor variables: climate PC1, climate PC2, body size, mixed-species flock participation, incubation period, migration, nest height, foraging height, forest cover, and diet. We found that Parahaemoproteus and Plasmodium prevalence was higher in species inhabiting open habitats. Tanager species with longer incubation periods had higher Parahaemoproteus prevalence as well, and we hypothesize that these longer incubation periods overlap with maximum vector abundances, resulting in a higher probability of infection among adult hosts during their incubation period and among chicks. Lastly, we found that Plasmodium prevalence was higher in species without migratory behaviour, with mixed-species flock participation, and with an omnivorous or animal-derived diet. We discuss the consequences of higher infection prevalence in relation to life-history traits in tanagers.

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.

Culicoides species community composition and feeding preferences in two aquatic ecosystems in northern Spain

Background

Aquatic ecosystems provide breeding sites for blood-sucking insects such as Culicoides biting midges (Diptera: Ceratopogonidae), but factors affecting their distribution and host choice are poorly understood. A study was undertaken at two nature reserves in northern Spain to examine the abundance, species composition, population dynamics and feeding patterns of biting midges between 2018 and 2019.

Methods

Culicoides were captured by light suction traps baited with CO₂ and by sweep netting vegetation. Blood meals and species identification of blood-fed specimens were determined using cytochrome c oxidase I subunit (COI) DNA barcoding. Multivariate generalized linear models were used to evaluate the associations between the abundance of Culicoides, the species richness and other parameters.

Results

The 4973 identified specimens comprised 28 species of Culicoides. These included two species reported for the first time in northern Spain, thus raising to 54 the number of Culicoides species described in the region. Specimens of all 28 species and 99.6% of the total specimens collected were caught in suction traps, while sweep netting vegetation revealed just 11 species and 0.4% of the total specimens. Midge abundance peaked in June/early July, with five species comprising > 80% of the captures: Culicoides alazanicus (24.9%), Culicoides griseidorsum (20.3%), Culicoides poperinghensis (16.2%), Culicoides kibunensis (10.7%) and Culicoides clastrieri (9.6%). DNA barcode analysis of blood meals from eight Culicoides species revealed that they fed on 17 vertebrate species (3 mammals and 14 birds). Species in the subgenus Avaritia were primarily ornithophilic, except for C. griseidorsum and C. poperinghensis. Host DNA from blood meals was successfully amplified from 75% of blood-fed females. A pictorial blood meal digestion scale is provided to accurately assess the blood-fed status of female Culicoides.

Conclusions

The large number of different blood meal sources identified in the midges captured in this study signals the likely importance of wild birds and mammals (e.g. red deer and wild boar) as reservoir/amplifying hosts for pathogens. Available hosts are more exposed to being bitten by biting midge populations in aquatic ecosystems in late spring and early summer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05297-5.

Seasonal Abundance of Culicoides at Yongsan US Army Garrison (USAG) and Camp Humphreys USAG, Republic of Korea, 2010-2013 and 2014-2017

Biting midges (Culicoides: Ceratopogonidae) were collected using New Jersey light traps at Yongsan US Army Garrison (USAG;urban), Seoul Metropolitan city and Camp Humphreys USAG (rural), Pyeongtaek, Gyeonggi-do (province), Republic of Korea, from May-October 2010–2013 and 2015–2017, to determine species composition and seasonal distribution patterns in urban and rural habitats. A total of 9,958 female (53.85%) and 8,533 male (46.15%) Culicoides comprising 16 species were collected. Overall, the most commonly collected species was Culicoides arakawae (74.3%), followed by C. circumscriptus (16.2%), C. kibunensis (2.5%), C. nasuensis (2.2%), C. clavipalpis (1.4%), and C. pallidulus (1.3%), while the remaining 10 species accounted for <2.1% of all Culicoides spp. collected. The 2 predominant species collected were C. circumscriptus (47.4%) and C. arakawae (33.4%) at Yongsan, and C. arakawae (90.4%) and C. circumscriptus (3.9%) at Camp Humphreys. The seasonal abundance of these 2 species varied between years and between sites but on average peaked in August–September for C. arakawae and June–July for C. circumscriptus. Annual variations in abundance were observed for most species collected during this study. Unusually high proportions of male specimens were observed for most species at both sites which may be due to the use of the New Jersey trap.

The flying activity of biting midges (Ceratopogonidae: Culicoides) in Verkiai Regional Park, southeastern Lithuania

Culicoides biting midges are small dipterous insects (Diptera: Ceratopogonidae) which are known to be vectors of arboviruses, bacteria, protozoan and helminth parasites that can cause disease and mortality in livestock and poultry globally. Detailed knowledge of the Culicoides species composition and biology is essential to assess the risk of the introduction and transmission of pathogens. The aim of this study was to obtain data on Culicoides species composition and flying activity in southeastern Lithuania and to determine the meteorological variables related to the abundance of Culicoides biting midges. Biting midges were collected in Verkiai Regional Park, southeastern Lithuania, using an Onderstepoort trap once a week from April to October 2016 and 2018, and from April to July 2019; 7332 Culicoides females belonging to 22 species were identified. Both morphology and DNA barcoding were used for identification. The number of specimens trapped was highest for the Obsoletus Group, followed by Culicoides kibunensis and Culicoides impunctatus. The highest relative abundance and diversity of biting midges were found in May and June. The number of trapped biting midges correlated positively with the mean air temperature. The first biting midges in spring were caught when the mean daily temperature rose higher than 10 °C. No Culicoides were detected when the air temperature dropped below 5 °C in autumn. Wind speed and air humidity had no statistically significant effect on Culicoides abundance.

Component-resolved microarray analysis of IgE sensitization profiles to Culicoides recombinant allergens in horses with insect bite hypersensitivity

Background

Allergy to bites of blood‐sucking insects, including biting midges, can affect both human and veterinary patients. Horses are often suffering from an IgE‐mediated allergic dermatitis caused by bites of midges (Culicoides spp). With the aim to improve allergen immunotherapy (AIT), numerous Culicoides allergens have been produced as recombinant (r‐) proteins. This study aimed to test a comprehensive panel of differently expressed Culicoides r‐allergens on a cohort of IBH‐affected and control horses using an allergen microarray.

Methods

IgE levels to 27 Culicoides r‐allergens, including 8 previously unpublished allergens, of which 11 were expressed in more than one expression system, were determined in sera from 347 horses. ROC analyses were carried out, cut‐offs selected using a specificity of 95% and seropositivity rates compared between horses affected with insect bite hypersensitivity (IBH) and control horses. The combination of r‐allergens giving the best performing test was determined using logistic regression analysis.

Results

Seropositivity was significantly higher in IBH horses compared with controls for 25 r‐allergens. Nine Culicoides r‐allergens were major allergens for IBH with seven of them binding IgE in sera from > 70% of the IBH‐affected horses. Combination of these top seven r‐allergens could diagnose > 90% of IBH‐affected horses with a specificity of > 95%. Correlation between differently expressed r‐allergens was usually high (mean = 0.69, range: 0.28‐0.91).

Conclusion

This microarray will be a powerful tool for the development of component‐resolved, patient‐tailored AIT for IBH and could be useful for the study of allergy to biting midges in humans and other species.

Biting midge dynamics and bluetongue transmission: a multiscale model linking catch data with climate and disease outbreaks

Bluetongue virus (BTV) serotype 8 has been circulating in Europe since a major outbreak occurred in 2006, causing economic losses to livestock farms. The unpredictability of the biting activity of midges that transmit BTV implies difficulty in computing accurate transmission models. This study uniquely integrates field collections of midges at a range of European latitudes (in Sweden, The Netherlands, and Italy), with a multi-scale modelling approach. We inferred the environmental factors that influence the dynamics of midge catching, and then directly linked predicted midge catches to BTV transmission dynamics. Catch predictions were linked to the observed prevalence amongst sentinel cattle during the 2007 BTV outbreak in The Netherlands using a dynamic transmission model. We were able to directly infer a scaling parameter between daily midge catch predictions and the true biting rate per cow per day. Compared to biting rate per cow per day the scaling parameter was around 50% of 24 h midge catches with traps. Extending the estimated biting rate across Europe, for different seasons and years, indicated that whilst intensity of transmission is expected to vary widely from herd to herd, around 95% of naïve herds in western Europe have been at risk of sustained transmission over the last 15 years.

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

Culicoides species from the Obsoletus group are important vectors of bluetongue and Schmallenberg virus. This group consists of several species that cannot easily be identified using morphological characteristics. Therefore, limited information is available about their distribution and habitat preferences. In this study, we aimed to elucidate the species composition of the Obsoletus group in three habitat types at climatically different latitudes across Europe. Traps were placed in three habitat types in three countries at different latitudes. After DNA extraction, biting midges were identified using PCR and gel electrophoresis. Extraction of DNA using Chelex proved to be a cost and time efficient method for species identification. A latitudinal effect on the relative abundance of species from the Obsoletus group was found. Species composition was unique for most country-habitat combinations. The majority of biting midges were either C. obsoletus s.s. or C. scoticus, and both species were found at all latitudes and habitats. Their wide distribution and their high abundance at livestock farms make these species likely candidates for rapid farm-to-farm transmission of pathogens throughout Europe. Our results emphasize the need to differentiate Obsoletus group species to better understand their ecology and contribution to pathogen transmission.