Morphology

FIGURE 10.2 Cuiicoides wiT^e«»«* larvae, fourth instar. (Photo by Bradley A. Mullens.)

consists of a pair of lateral arms and a median region supporting two to four combs which overly one another. The epipharynx is rocked back and forth by muscles attached to the lateral arms and functions by helping to shred solid food and move food items posteriorly into the alimentary tract. In species which feed primarily on detritus and microorganisms, the combs apparently serve to strain material entering the mouth cavity. The number of pharyngeal combs and the degree of sclerotization of the epipharynx are highly variable, reflecting the diversity of ingested food items and feeding behaviors exhibited by ceratopogonid larvae.

Pupae are typically brownish in color, with a pair of relatively short but conspicuous prothoracic respiratory horns arising at the anterior end (Fig. 10.IC). Close inspection reveals numerous, tiny spiracular openings at the tip. The respiratory tubes repel water, enabling aquatic forms to hang at the water surface, where they can obtain air during metamorphosis to the adult stage. A pocket of air beneath the developing wings provides additional buoyancy to keep the pupa at the water surface. Cuticular features in the form of tubercles, spines, and setae provide valuable taxonomic characters for identification of pupae to species.

Adult Cuiicoides midges (Fig. 10.ID) are tiny, usually 1—2.5 mm in body length. Their mouthparts are adapted for biting or piercing tissues and are especially well developed in blood-sucking species (Fig. 10.3). In females, the mouthparts are surrounded by a fleshy extension of the labium called a proboscis, which is relatively short, about as long as the head. It consists of an upper labrum/epipharynx, a pair of bladelike mandibles, a pair of laciniae (maxillae), and a ventral hypopharynx bearing a median, longitudinal groove along which saliva is passed as the female feeds. The mandibles bear a row of teeth along the inner edge near the tip, which is used to lacerate the skin while biting. The mouthparts of males are generally reduced and are not used in blood feeding.

Associated with the mouthparts are a pair of 5-segmented maxillary palps. The third segment is typically enlarged and bears a specialized group of sensilia located in a depression, or sensory pit, that serves as a sensory organ. The adult antennae are 15-segmented and consist of a basal scape, an enlarged pedicel containing Johnston's organ, and 13 flagellomeres. The antennal segments bear differing numbers of small sensory pits (sensilia coelocon-ica), the number and pattern of which provide important taxonomic characters. The number of segments bearing sensory pits appears to be correlated with host feeding; species which feed primarily on birds generally have more sensory pits than those which feed on mammals. In males, flagellomeres 1—8 possess whorls of long setae, which increase their sensitivity as mechanoreceptors and give them their plumose appearance. The wings possess a characteristic venation that distinguishes the ceratopogonids from other groups of flies. More important, however, are the distinctive wing patterns of the genus Cuiicoides, which are the basis for most species determinations in this large and important group. The darker areas of the wings are not pigmented, but represent the density of tiny setae (micro- and macrotrichia) on the wing surface.

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