Open access peer-reviewed chapter

Morphological Keys for the Identification of Tunisian Culicoides Biting Midges (Diptera: Ceratopogonidae)

By Darine Slama, Emna Chaker and Hamouda Babba

Submitted: September 27th 2020Reviewed: February 16th 2021Published: September 8th 2021

DOI: 10.5772/intechopen.96656

Downloaded: 23

Abstract

Culicoides biting midges are tiny blood-feeding insects of several diseases with veterinary and public health significance, including Bluetongue in ruminants, African horse sickness in equids and filarial diseases like Onchocercosis and Mansonellosis affecting various species such as humans. Their identification depends basically on the microscope examination of key morphological characters. Consequently, identification keys are important to any non experiment working with these biting midges. The Tunisian fauna of Culicoides biting midges consists of 35 species, whose morphological delineation may be troublesome for non-taxonomists. In response to this situation, and for the first time a key to the adult Culicoides species in Tunisia was prepared.

Keywords

  • Culicoides
  • morphological identification
  • taxonomy
  • Tunisia
  • vectors

1. Introduction

CulicoidesLatreille, 1809 (Diptera: Ceratopogonidae) is a genus of biting midges, containing 1368 species divided into numerous subgenera [1]. Indeed, they are vectors of a variety of pathogens, including protozoans [2], filarial parasites [3] such as avian haemosporidians [4] and Tetrapetalonema spp. [5, 6, 7]. More than 50 viruses have been isolated from Culicoidesspp. worldwide [8], such as African horse sicknes virus (AHSV), Bluetongue virus (BTV), Epizootic hemorrhagic virus (EHDV), Schmallenberg virus (SBV), or Oropouche virus (OROV) [9]. These viruses are responsible for outbreaks of non-contagious disease in ruminants, causing severe economic loses [10]. In the Mediterranean basin as well as sub-saharan Africa, the main vector of BTV and AHSV is Culicoides imicola[11]. Moroever, other Paleartic Culicoidesspecies, within the subgenera Avaritia, such as C. obsoletus, C. scoticus, C. dewulfiand C. pulicarisare also known or potential BTV vectors [12, 13]. The recent BTV outbreaks in Tunisia demonstrate how a relatively neglected arthropod vector group can rapidly augment in interest. Thus identification of the vector is an important step in the epidemiology of vector born diseases. For instance, Tunisian fauna of Culicoidesincludes 35 distinct species [14]. Indeed, at the regional level, there are no proper morphological keys to Tunisia CulicoidesSpecies. This can cause a major confront in the control effort as the accurate identification of vectors is crucial for vector incrimination. In this context, a morphological identification key was prepared for the adult of the recorded Culicoidesspecies in Tunisia as simply as possible, using the most important characters. Hopefully, this will aid public health workers, students and entomologists for rapid and accurate identification of Culicoidesto the genus and species levels.

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2. Methods

2.1 Trapping methods

Culicoidesspecimens used herein were collected at different locations, in studies conducted in Tunisia. Collection sites were selected based on their characteristics, including presence of animals, type of vegetation, and degree of urbanization. Two models of light traps: home-made miniature using CDC (Centre of Disease Control, Atlanta, USA) and OVI (Onderstepoort Veterinary Institute) were used.

2.2 Samples processing

All insects were collected in a beaker filled with 70% ethanol. Sampled Culicoideswere separated from other insects and identified according to wing characters using a stereomicroscope. Culicoidesmidges were separated according to sex. Specimens were dissected on a glass slide separating the terminal part of the abdomen, wings and the entire head with a fine needle and mounted in a mix of Balsam Alcohol-Phenol for later identification. Species identification was made according to different morphological keys [15, 16, 17].

2.3 Morphological characterization

The morphological characteristics used here were based on original observations and previous usage in the litterature [15, 17, 18] (Figure 1). Several morphological characters were examined during the preparation of this morphological identification keys. The following main features were considered: Head(Eyes; Antenna (short segments: shape; sensilla coeloconica (Presence); antennal ratio XI/X ratio, length of segment XI divided by length of segment X; sensilla coeloconica, segments III to VI (Presence); sensilla coeloconica, segments VII to X (Presence); sensilla coeloconica, segments XI to XV (Presence)); Palpus(3rd palpal segment (shape, number of sensory pits, single sensory pits (opening versus depth)); Abdomen: Spermathecae (spermathecal duct at the end of the sclerotized ring, number, size, shape, abdominal sclerites (presence or absence)); Wingspale or dark spots (presence/absence), distribution, size.

Figure 1.

Adult of Culicoides (Diptera: Ceratopogonidae).

Representative Culicoidesspecimens for each species available were selected and relevant characters were image captured with a digital camera through Leica microscopy. For some illustrations of Tunisian Culicoidesspecies we used a drawn image used by (18).

3. Results and discussion

The present works illustrated the identification keys to adults of 35 Culicoidesspecies (Diptera: Ceratopogonidae) which have been recorded in Tunisia (Table 1). Indeed, comprehensive identification keys of genera and species of Culicoideswere elaborated. The simplified keys allow distinguishing each genus, subgenus and species based on the most important morphological features. Nevertheless, identification keys are fundamental for anyone dealing with insects of medical and veterinary significance, such as Culicoidesbiting midges. They are aimed to provide a guide for those interested to identify field-collected specimens obtained for many purposes and different type of studies. Indeed, identification keys especially those accompagnied by digital photographs and line drawing illustarting taxonomically relevant characters, are useful for species identification of Culicoidesmidges [15]. In Tunisia, even though the first record of Culicoideswas documented in 1981 [15], field identification of this medically important group of insects has been carried out referring to the basic features and published literature. Indeed, in the case of the Tunisian biting midge fauna, [15] (in French) contain only restricted geographical areas, do not contain the new species records [14, 16, 19]. In the morphological identification keys presented here are accompanied by digital photographs taken from original specimens, which make the keys more user-friendly and facilitating the accurate identification of species.

Table 1.

Key to Culicoidesspecies in Tunisia based on female and male morphology.

: photo of different part (wing, head, 3rd palpal and spermatheca) of Culicoidesspecies were taken from Mathieu et al 2012


: photo of genitalia taken from Turgut F, 2018


: photo of drawn part of Culicoideswere taken from Delecolle JC, 1985


Other image illustarting the different parts of Culicoidesbody in this chapter were taken from the Laboratory of Medical and Molecular Parasitology-Mycology LP3M (code LR12ES08), Department of Clinical Biology B, University of Monastir, Tunisia

One of the main limitations of the keys is that the males are incomplete. Therefore, species characterizations were not illustrated in the identification key based on male morphology. Furthermore, some species were not of good quality to take a clear photograph. For this, keys were supplemented with illustrations adapted from published literature [17, 18].

To the author’s knowledge, these are the first keys prepared for Tunisian Culicoides fauna which are meant as an aid to the rapid identification.

Key forCulicoides(Diptera: Ceratopogonidae) females from Tunisia

11 functional spermathecae………………………………………..2
2 functional spermathecae………………………………………..5
3 functional spermathecae………………………………………..C. saevus
2Sensilla coeloconica: presence on segments III to XI, presence on segments XII to XIIII…………………………………………
Spermatheca narrow opening……………………………………..3
Sensilla coeloconica: absence on segments XII to XV, presence on segments III, VIII and X……………………………………..
3rd palpal segment slender with slightly swollen, multiple irregular pits………………………………………………………
Spermatheca wide opening, oval, elongated, heavily curved in the middle…………………………………………………………4
3Pharynx posterieur armature: presence…………………………..
Sensilla coeloconica: absence on segment XV…………………..
Wing: r-m cross vein, presence on dark spot in the corner with M1 vein……………………………………………………………C. circumscriptus
4Pale wing with only 1 dark spot cover the second radial cell…….
Antennal XI/X ratio: inferior or equal to 2………………………C. parroti
Wing with 1 ore more pale spots…………………………………
Antennal XI/X ratio: inferior or equal to 2………………………C. puncticollis
5Eyes: inter-ocular space: joined…………………………………
3rd palpal segment: Multiple irregular pits………………………
Wing: 1 ore more pale spots well defined……………………….
Pharynx posterieur armature: Presence…………………………..6
Eyes: Separated………………………………………………….
3rd palpal segment: One single sensory pit, triangular, wide opening and shallow pit…………………………………………..
Wing: 1 or more pale spot………………………………………..
Pharynx posterieur armature: absence……………………………7
6Wing: 2 pale spots fused in the middle basal of M1…………….
Presence of dark spot in r3……………………………………….
Leg: Middle leg: Absence of spines on 4th tarsomere …………C. newsteadi
Wing: pale spot in the base of M1 ………………………………
Leg: Middle leg: Presence of spines on 4th tarsomere………….C. punctatus
Wing: pale spot over r-m crossvein fused with the m2………….
Presence of dark spot in r3………………………………..
Leg: Middle leg: Absence of spines on 1st to 3rd tarsomere…..C. imicola
7Wing: Absence of pale spot (base wing)………………………..
Antenna: antennal XI/X ratio: inferior or equal to 2……………8
Wing: Presence of pale spot at thebase of the wing……………..
Antenna: I.A: total lengthe of 5 apical segments [11, 12, 13, 14, 15]/total length of 8 basal segments [3, 4, 5, 6, 7, 8, 9, 10]: superior to 1,12…………………………….…C. jumineri
8Presence of sensilla coeloconica on the 6th segment…………….9
Absence of sensilla coeloconica on the 6th segment…………….C. pseudojumineri
9Size of 2 spermatheca equal to 50 μ………………………………C. jumineri var
Size of 2 spermatheca superior to 30 μ……………………………C. heteroclitus
Size of 2 spermatheca inferior to 58 μ…………………………….10
10Presence of sclerotized ring at the end of the spermatheca duct…C. gejgelensis or C. cataneii var
Absence of sclerotized ring at the end of the spermatheca duct…11
11Length of palp superior to 185 μ………………………………….C. pseudopallidus
Length of palp superior to 164 μ………………………………….C. cataneii
12Absence of sensilla coeloconica on the segment XV…………….13
Absence of sensilla coeloconica on all segments…………………16
13Length of total antennal segment superior to 517 μ………………C.odiatus
Length of total antennal segment inferior to 488 μ……………….14
14Palp (3/1 + 2) ratio, length of 3rd palpal segment divided by length of 1st and 2nd palpal segment: inferior to 1, 07………….15
152 spermathecae: pyriform, size: superior to 58 μ…………………C. langeroni
2 spermathecae ovoid, size: inferior to 50 μ………………………C.pseudolangeroni
Wing: absence of pale spots in the distal part of r3, m1, m2…….
3rd palpal: swollen with narrow opening and deep pit…………C. semimaculatus
Presence of more than one pale spot in the distal part of r3, m1, m2…………………………………………………………………
3rd palpal segment strongly swollen, with narrow opening single sensory pits and deep pit…………………………………………C. paolae
Length of total antenna: inferior to 300 μ……………………….C. marcleti
Length of total antenna: superior to 363 μ……………………….16
16I.A: inferior to 1.03………………………………………………C. kingi
I.A superior to 1.20……………………………………………….17
17Palp (3/1 + 2) ratio: inferior to 1.13……………………………….C. corsicus
Palp (3/1 + 2) ratio: superior to 1.26..…………………………….18
18Presence of chitinized thorn at the beginning of the pharynx posterior………………………………………………………….C. sahariensis
Presence of 1 to 3 thin thorns at the beginning of the pharynx posterior………………………………………………………….C. longipennis
Presence of chitinized thorn at the beginning of the pharynx posterior………………………………………………………….19
19Presence of pale spot r3, m1, m2, anal cell, pale spot in distal part: Presence of 2 pale fused, 2 pale spot separated……………C. maritimus
Absence of pale spot r3, m1, m2 and anal cell……………………20
20Absence of pale spots…………………………………………….
Presence of sensilla coeloconica on all short segments and absent on all long segments……………………………………………..C. sergenti
Presence of pale spots……………………………………………
Sensilla coeloconica not present on all short segments…………..21
21Presence of pale spots
Sensilla coeloconica on all short segments but often absent on segment X………………………………………………………..
I.A: superior to 1 μ……………………………………………….
3rd palpal segment, triangular, swollen, sensory pit wide openingC. sp near kibunensis
Presence of pale spot……………………………………………..
Presence of sensilla coeloconica on segments VII, VIII, IX and X
Presence of sensilla coeloconica on segments XI to XIIII………
I.A inferior to 1 μ
3rd palpal segment, triangular and moderate swollen, single sensory pit, wide opening and swollen pit……………………….C. kurensis

Key forCulicoides(Diptera: Ceratopogonidae) males from Tunisia.

1Aedeagus: bifid………………………………………………….2
Aedeagus: not bifid……………………………………………..3
2Presence one dark spot on the 2nd rad cell………………………C. parroti
3Welded paramers with distal part consisting of spoon shaped……C. heteroclitus
Paramers separated, pointed with 7 to 8 sawteeth on its posterior edge………………………………………………………………C. sergenti
Paramers terminated by a succesion of thorns and presenting a lobe……………………………………………………………….4
Paramers with tapered pointed end………………………………7
4Arm of the aedeagus with lateral process………………………..5
Arm of aedeagus without lateral process…………………………6
5Body of aedeagus: rectangular, elongated……………………….C. corsicus
Body of aedeagus: short…………………………………………C. marcleti
6Body of aedeagus: triangular with truncated end terminating in tiny teeth………………………………………………………….C. longipennis
Body of aedeagus: Triangular with pointed distal end………….C. sahariensis
7Ventral membrane spiculated…………………………………….8
Ventral membrane not spiculated…………………………………12
8Body of aedeagus: short and large………………………………9
Body of aedeagus: Triangular……………………………………10
Body of aedeagus with rounded apex……………………………
Absence of ventral apodeme……………………………………..C. circumscriptus
Body of aedeagus without rounded apex………………………..
Well developped ventral apodeme………………………………..C. kingi
10Body of aedeagus large in the distal part, rounded end ………….C. imicola
Center of the aedeagus body occuped by a chitinized point directed forward………………………………………………….11
11Basal quarter of the wing covered by a pale spot…………………C. jumineri
Slight lightening at the base of the wing………………………….C. pseudopallidus
Wing with pale spots………………………………………………16
Absence of pale spots at the base…………………………………17
12Body of aedeagus: triangular, wide basal arch andrectangular distal part…………………………………………………………C. paolae
Body of aedeagus: triangular…………………………………..13
Body of aedeagus: rectangular…………………………………..15
13Body of aedeagus: very little developped……………………….
Arm of aedeagus: very long………………………………………C. saevus
Arm of aedeagus: well developped………………………………
Arm of aedeagus: short…………………………………………..14
14Process: very short, broad-based…………………………………C. langeroni
Process: long, with a narrow base………………………………..C. pseudolangeroni
15Body of aedeagus: rectangular, large…………………………….C. cataneii
Body of aedeagus: elongated, narrow……………………………C. gejgelensis or C. cataneii var
16Single and big pale spot in the basal half of m1………………….C. punctatus
2 or bilobed spot in the basal half of m1………………………….C. newsteadi
17Arms of appendix: horse ear shaped well developped…………..
Paramers with additional lobe well developped, wide terminal part, with 5 to 6 thiks tips…………………………………………C. semimaculatus
Aedeagus without additional appendices on the arms…………….
Paramers without additional lobe…………………………………18
18Presence of spot (proximal part of m1)…………………………C. pseudojumineri
Presence of pale spot m4 cut by the edge of the wing …………..
Presence of spot (proximal part of m1)…………………………
Presence of pale spot m4 not cut by the edge of the wing ……….C. jumineri var

4. Conclusion

The simplified keys, would contribute towards improving research capacity among researchers in Tunisia as the identification is a fundamental requirement for anyone dealing with medically important insects.

Acknowledgments

We thank the heads of Hygiene Services of Public Health, all of whom facilitated the field work together, and the health agents who contributed to the achievement of this survey. This study was carried out with the financial support of the Research Lab, Laboratory of Medical and Molecular Parasitology-Mycology LR12ES08, Department of Clinical Biology B, Faculty of Pharmacy, University of Monastir, Monastir, Tunisia.

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Conflict of interest

The authors declare no conflict of interest.

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Darine Slama, Emna Chaker and Hamouda Babba (September 8th 2021). Morphological Keys for the Identification of Tunisian <em>Culicoides</em> Biting Midges (Diptera: Ceratopogonidae), The Wonders of Diptera - Characteristics, Diversity, and Significance for the World's Ecosystems, Farzana Khan Perveen, IntechOpen, DOI: 10.5772/intechopen.96656. Available from:

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