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By their annoying attacks in tremendous numbers, Culicoides species have gained notoriety as pests on beaches and in coastal Swamps throughout the world. Recreation areas in the mountains also have their quota of these pestiferous species. In the West Indies the most widespread and troublesome pest is C. furens, which in some coastal areas is troublesome enough to retard the development of otherwise magnificent resorts (Myers, 1985; Adamson, 1939; Linley and Davies, 1971). In special areas C. phlebotomus, C. barbosai Wirth and Blanton, and C. melleus are also a problem, along with another bloodsucking ceratopogonid, Leptocomops bequaerti (Kieffer) (Painter, 1927; Linley and Davies, 1971). Fourteen of the 24 West Indian species have been recorded as biting humans.
Linley and Davies (1971) reviewed the problem of sandflies versus tourism in the West Indies, summarized the biology of the most important species, and made recommendations for control. The main
thrust of their entire article is toward ways of avoiding a sandfly problem whenever possible rather than trying to control an already existing one. They “advise that intending developers should fully investigate the sandfly situation before commencing their projects, since control measures forced upon them later may be very expensive.”
Linley and Davies further stated: “One point that should not escape would-be developers is the following. In fast-growing areas, such as parts of Florida, small towns are often established in desirable areas, and combined interest ensures the necessary funds to deal with insects on a coordinated basis. An entirely different situation exists in a remote island locality. We saw instances of single hotels sited in complete isolation, literally surrounded by enormous swamps. The tourist in this situation is important only to the promoters, and they alone must bear the entire and frequently formidable cost of insect control.”
The structure of Culicoides adults has been described by Carter et al. (1920), Jobling (1928), Tokunaga (1937), Gad (1951), Wirth (1952a), Wirth and Blanton (1959), Jamnback (1965), and Atchley (1967, 1970). In the following brief descriptions the most important characters used in Culicoides classification are defined.
Head.—The head is subspherical, with the anterior surface somewhat
flattened and in line with the anterior surface of the proboscis. The compound eyes are large, reniform, and more or less contiguous above the bases of the antennae. They may be bare or with short pubescence between the ommatidial facets. The
degree of eye separation or contact is often useful in distinguishing species. In the angle between the eyes on the frons is an interocular seta
and above this is often a transverse
suture that marks the separation of the frons and vertex. The antenna has 15 divisions, termed segments in this bulletin for convenience, although it is recognized that the 13 divisions of the flagellum are not true segments in the morphological sense. The basal segment or scape is ringlike, incorporated in the head capsule, and hidden by the greatly enlarged pedicel. The first flagellar segment is slightly enlarged and always bears several small sensory pits each surrounded by minute setae. Some or all of the distal segments also bear these sensory tufts; their number, shape, and distribution are of great importance in classification. In the female the first eight flagellar segments are short and bear long verticils basally. The five distal segments are more elongated and without verticils. The ratio of the combined lengths of the five elongated distal segments divided by the combined lengths of segments 3–10 forms the antennal ratio (AR). In the male the pedicel is more enlarged than in the female, and the transition in lengths of the flagellar segments occurs between segments 12 and 13. Of segments 3– 12, each has a whorl of greatly elongated, erectile verticils forming a sparse to dense plume. The mouthparts are well developed, often as long as the head capsule itself, and stronger in the female than in the male. In females of most species they are fitted for piercing and bloodsucking. They consist of six slender, distally toothed blades of subequal lengths, including a strong upper labrum-epipharynx, a pair of
maxillae, a pair of strongly toothed mandibles, and a median tubular hypopharynx. These parts are enclosed in a proboscis formed by the fleshy part of the labium. The relative length of the proboscis is of value in classification and is expressed as the proboscis/head ratio (P/H ratio), which is obtained by dividing the distance from the end of the labrumepipharynx to the tormae by the distance from the latter to the interocular setal base. The maxillary palpus is five-segmented, and the third segment is somewhat swollen and on the distal part of the medioventral surface bears a specialized sensory pit or group of sensilla, which forms an important taxonomic character. The palpal ratio (PR) is the length of the third palpal segment divided by its greatest breadth.
Thorax.-The thorax is moderately broad and convex above, arched anteriorly, and projecting slightly over the head. Dorsally it bears a pair of small depressions behind the humeri, known as the humeral pits, which have been assumed to be sensory but whose exact function is obscure. In various species the disk of the mesonotum is ornamented with a distinctive pattern, best seen in fresh or dried specimens, but usually visible to some degree in slide-mounted material. The legs are slender without special armature, but the apex of the fore tibia bears a small spur and tuft of modified hairs, and the tip of the hind tibia bears an anterior spur and two transverse rows of modified spinose hairs. The “hind tibial comb” includes only the longer spines in the distal row and is of some value in classification. The fourth tarsomere is usually cylindrical but in a few groups is cordiform. The claws are small and equal on all legs, simple in the female but divided at the apices in the male. The empodium is vestigial. Wing.—The wings bear dense microtrichia, the size and pigmentation of which give rise to the characteristic pattern of dark or light spots, and more or less abundant macrotrichia or longer hairs. The color pattern of spots or bands is characteristic for each species and is of primary importance in classification; however, in some groups of species it is poorly developed or even absent. In the males the wing is longer and narrower than in the female, and the color pattern is less contrasting. The wing length is measured from the basal arculus to the wing tip. The costa usually extends to more than half the wing length. The costal ratio (CR) is the value obtained by dividing the length of the costa by the wing length. There are, with rare exceptions, two complete radial cells formed by the more heavily sclerotized radial branches; usually the second or distal one (2RC) is broader and longer than the first, which is often slitlike. We used the Tillyard modification of the Comstock-Needham system of wing venation, in which from front to back the branches of the anterior fork are called M1 and M2 and those of the posterior fork are M3+4 and Cu1. The color of the halter is also useful in species separation. Abdomen.—The female abdomen is relatively stout and the apex some
what tapered, with a pair of small rounded cerci visible below the ninth tergum. Internally the female possesses from one to three sclerotized spermathecae, which are usually oval to pyriform, with the slender bases of the ducts sclerotized for a short distance. The spermathecae are joined by hyaline ducts to a common duct, and at the juncture there is usually a small sclerotized ring. In most species with two sclerotized spermathecae there is also a small rudimentary third one. The number and shapes of the functional spermathecae and the presence or absence of a ring are important in classification. The length of the spermatheca is measured in the axis of the base of the duct and includes the sclerotized part of the duct. The male abdomen is slender and bears the prominent genitalia terminally. These are of primary importance in group classification and species identification. The ninth segment is in the form of an irregular sclerotized ring consisting of the fused tergum and sternum. The ninth tergum forms an expanded plate, convex externally and hollowed out mesally, and bearing the anus flanked by a pair of membranous cerci on the ventromesal face. The hind corners of the ninth tergum are frequently expanded as a pair of apicolateral processes. The ninth sternum is much shorter than the tergum, usually with a caudomedian excavation on its hind margin, where the base of the aedeagus articulates at the lateral corners. The forcepslike genital append ages or gonopods arise laterally at
the base of the tergum and are twosegmented. The enlarged basal Segment or basistyle bears two internal processes at the base, a mesally directed ventral root and an anteriorly directed dorsal root, the latter articulating directly with the base of the paramere. The distal segment (dististyle or clasper) is setose and slightly swollen at the base, slender and nearly bare distally with an incurved point. When not extended, it is folded mesad across the mesal face of the ninth tergum. The aedeagus is usually a Y-shaped structure with a median process directed ventrocaudad, forming a sclerotized support on the ventral surface of the male genital duct.
The parameres are usually a pair of sclerotized internal rodlike sclerites, each with knobbed base and ventrally directed distal point. They are subject to great modifications in the shape and direction of the basal knob, the middle stem, or the distal point. In some groups of species the parameres may fuse mesally in part or completely in a platelike structure. Although morphologists suggest that it is more appropriate to use the term paramere for the primary gonopod, here called the basistyle and dististyle, and the term claspette for the internal sclerite, here called the paramere, we prefer to follow the traditional usage among ceratopogonid taxonomists.
Adult Food Habits and Autogeny
The males feed on nectar from flowering plants and females may increase longevity by doing so. Without sugar, laboratory-bred C. barbosai adults were all dead within 4 days, but with sugar available, males lived up to 13 days and females up to 17 days (Linley, 1966b). In C. obsoletus (Meigen) females, longevity increased from 10 to 51 days in New York when they were fed sugar (Jamnback, 1961).
Only Culicoides females take a blood meal. In most species a blood meal is required for egg maturation. In some species, which are autog2nous, eggs may be matured on the first gonotrophic cycle without a blood meal. These flies obtain nutri
tion for egg development from fat bodies stored during the larval stages. Maturation of a second and subsequent egg batches in such species is dependent on a blood meal, and a meal is needed for each batch of eggs. Facultative autogeny takes place to a variable degree in C. melleus (Linley, 1969), C. furens and C. barbosai (Linley, 1966b; Linley et al., 1970b), C. sanguisuga (Coquillett) (Jamnback, 1965), C. waringi Lee and Reye and C. mackerrasi Lee and Reye (Dyce and Murray, 1967), and other species. Gluchova (1958) showed that the number of blood meals and ovarian cycles could be ascertained by the number of follicular relicts in the ovaries after oviposition. She identified up to four ovarian cycles in wildcaught C. grisescens Edwards, but Lewis (1958) found more than one relict body difficult to observe in C. furens and C. barbosai. Some species with reduced mouthparts (low number of mandibular teeth) are not known to take a blood meal: C. bambusicola Lutz (Lee, 1968), C. circumscriptus Kieffer (Gluchova, 1958), C. bermudensis Williams (Williams, 1961), and C. dendrophilus Amosova (Amosova, 1959). Linley et al. (1970b) found in Florida that C. furens females that were caught attempting to bite in nature were all parous (i.e., had relict ovariole dilations from previous ovipositions). They concluded that this species is probably 100 percent autogenous. They showed that C. furens exhibits a seasonal change in egg productivity of autogenous females in a population, varying from a minimum of 43 eggs per female in the smallest individuals (mean wing length 0.91 mm.) emerging in September to a maximum of 81 eggs deposited by larger females (wing length 1.15 mm.) emerging in March after developing in the cooler part of the year. The adult feeding habits of the West Indian Culicoides can be summarized as follows: Feeding on man.-barbosai, floridensis, foci Ortiz, furens, hoffmani Fox, insignis Lutz, loughmani, melleus, pamamensis Barbosa, paraensis (Goeldi), phlebotomus, pusillus Lutz, trilineatus Fox, and trinidadensis. Feeding on horse, donkey, mule.— arubae Fox and Hoffman, foci, fu
rens, and heliconiae Fox and HoffII].8.1).
Feeding on cattle.—insignis.
Feeding on bird.—archboldi Wirth and Blanton and hoffmani.
Hosts unknown.—borinquemi Fox and Hoffman, bredini Wirth and Blanton, decor, dominicanus Wirth and Blanton, farri Wirth and Blanton, guadeloupensis Floch and Abonnenc, and jamaicensis.
Mating (Downes, 1955) typically takes place in flight. The males form swarms and as the females fly through the swarms they are captured by the males. A few species will mate without swarming, with both sexes running or crawling around on the soil or vegetation near the potential larval habitat and mating on contact (Downes, 1958). C. melleus is a West Indian species with this habit (Linley, 1969; Wirth, personal observation). In some species both sexes are attracted to the adult host where the males mate with the females shortly after the latter have fed (i.e., C. nubeculosus (Meigen) in Russia and C. utahensis Fox in western North America).
While swarming the males bring the setae of the antennal plumes to an erect position (Downes, 1955 1958), where they serve in auditory recognition of the wing beat frequency of the female. At all other times they are folded. The mating posture (Pomerantzev, 1932) is normally end to end facing in opposite directions with the male claspers pointing to the head of the femal and the ventral parts of the genitalia