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

Abstract

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.

Keywords: Barcoding; Biting midges; Dynamic populations; Freshwater habitats; Host blood meals; Species richness.

Fig. 1

Location of the sampling sites and traps used to collect Culicoides biting midges. a Map of the Basque Country in northern Spain showing the two aquatic sites: Urdaibai (U) and Salburua (S). b methods of collection (sweep net and CDC traps, respectively). c Photograph of both settings

Fig. 2

Venn diagram showing the presence of Culicoides biting midges in two aquatic ecosystems in northern Spain

Fig. 3

Seasonal dynamics of Culicoides species from 1 May to 31 October 2019 at two sites in northern Spain. Each point denotes the mean (± standard error) number of Culicoides caught per trap

Fig. 4

Different stages in the digestion of blood meals in Culicoides biting midges. The numbers 2–6 indicate the respective stages of blood meal digestion for Culicoides females. Stage 2: undigested (engorged abdomen showing intense dark-brown or fresh red tones) Stage 3: early digestion (engorged abdomen showing first signs of digestion with abundant dark blood). Stage 4: advanced digestion (abdomen showing advanced digestion but visible blood remains). Stage 5: pregravid (abdomen showing early egg formation mixed with a reddish tegument). Stage 6: gravid (engorged abdomen showing egg formation with no sign of blood). The upper row of images shows whole specimens of Culicoides and the lower row of images shows two different forms of the abdomens at the respective stage. Stage 1 (not shown) is the nulliparous stage