the feeding apparatus of biting

Every known method of control for such pests should be available to sanitary corps members. Parasitic worms in the blood cavity of the insect can even be transmitted via the small intestine, at least by flies. This condition occurs especially in the study of the feeding apparatus of the Diptera.

The top of the skull is called the vertex {Vx), between the antennae is the frontal region (Fr), and from the latter extends downwards a broad lobe, which is the clypeus (Clp). Its two basal plates, mentum (Mt) and submcntum (Suit), together postmcntum, He in the back wall of the head below the cervical foramen. Position of hypopharynx between clypeus and labrum in front and pre-.

In front of the hypopharynx at the base of the clypeus is the mouth (Mth), behind at the base of the prementum. The first part of an insect's alimentary canal, which is of ectodermal derivation, is the stoiiwdacum.

Fig. 1. — Head and mouth parts of a cockroach, Blattella germanica (L.).

NO. I BITING AND DISEASE-CARRYING FLIES SNODGRASS 7

MOSQUITOES. FAMILY CULICIDAE

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NO. I BITING AND DISEASE-CARRYING FLIES SNODGRASS 9

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The maxilla is provided with protractor and retractor muscles (J), the protractors being inserted at the end of the apodeme, the retractors at the base of the galea and palpus. The hypopharynx has no muscles and therefore no independent movement; it probably serves mainly for the hypodermic injection of the saliva into the wound made by the other stylets. The elongated labium of the mosquito corresponds to the distal appendicular part of the labium in the cockroach, known as the pre-.

The sclerotized outer wall of the dipterous labium, proximal to the labella, is called the theca (The). The only muscles attached to the base of the labium are a pair that arises on the maxillary apodemes (J), which, as the labium can have little. The position of the stylets within the labial trough is shown in cross-section of the proboscis at G of Figure 4.

Finally, beneath the hypopharynx against the floor of the labial gutter are the maxillary leaflets (Mx). The saliva is directed in the opposite direction from the tip of the proboscis through the salivary duct (sc) of the hypopharynx.

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NO. I BITING AND DISEASE-CARRYING FLIES SNODGRASS 1 5

SAND FLIES. FAMILY PSYCHODIDAE

Most members of the psychodid family are small, harmless, nectar-feeding flies that look like tiny moths because of their thick hair and the way their wings are spread flat or slanted over their bodies when resting. Species from the genus Phlebotomus Rondani, known as sand flies, however, are bloodsuckers and have painful bites. There are relatively few species, but they are widespread, especially in warm areas; only one species has been recorded in the United States.

The wing ornamentation shows that the insect belongs to the Psychodidae, although otherwise it bears little resemblance to other members of it. The front of the head (A) has the same structure as in the mosquito. Fr) consists of a median bar extended above the antennae, and forked below into a pair of arms extending laterally to the lower ends of the eyes. The maxillae differ from those of the mosquito in that they are suspended by a pair of slender rods which lie in the membranous posterior wall of the head (C, St) and are attached to the cranial edges below the neck foramen.

The theca of the broad, strong labium (C, The) bears a pair of soft labellum at its end; proximal toit's base is a small triangular plate (Pint), probably a postmental sclerite. The musculature of the mouthparts of Phlebotomus is fully described by Christophers, Shortt and Barraud (1926). As in the mosquito, the maxillae alone are capable of an independent back and forth movement on the head.

While the mandibles normally lie between the labrum and the hypopharynx, according to Adler and Theodor (1926) they are moved apart during feeding, perhaps to enlarge the wound and allow the hypopharynx to do so. The canal of the latter is thus closed by the hypopharynx, and the slender spines at the ends of the two opposite leaflets (Fig. 7 F, G) interlock to form a sieve guarding the entrance to the alimentary canal.

Fig. 7. — Head and mouth parts of Flcbotomns verrucariim Towns., female.

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BITING MIDGES. FAMILY HELEIDAE

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BLACK FLIES. FAMILY SIMULIIDAE

The members of this family, known as black flies because of their dull and blackish color, oral and buffalo because of the bulging appearance of the thorax (fig. 9), are small flies characterized by the strongly sloping front of the thorax and the hanging head, which hangs from the neck below the level of the body. . Only the females are known as leeches; The males are said to have the same mouthparts as the females, but the stylets are much weaker.

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HORSE FLIES. FAMILY TABANIDAE

Pmt, postmentum; pt, fovea tentorialis posterior; sc, ductus salivarius; SID, ductus salivarius; SIO, orificium salivarium; Sorbere, sentinam salivarem; St, log; Arca archa; Tnt, tent;y, cornu sentinae cibarialis.

Fig. ii. — Horse fly, Tabanus, head, mouth parts, and sucking apparatus.

NO. I BITING AND DISEASE-CARRYING FLIES SNODGRASS 31

SNIPE FLIES. FAMILY RHAGIONIDAE

ROBBER FLIES. FAMILY ASILIDAE

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THE CYCLORRHAPHA

I BITES AND DISEASE CARRIERS- SNODGRASS 35proboscis of Nematocera and Brachycera, called haustellum proboscis of Nematocera and Brachycera, called haustellum (Hstl). The anterior wall of the socket contains one or two clypeal plates (dp) and supports the maxillary palp (MxPlp); inside the rostrum are a pair of labral apodemes, cibarial pump and salivary pump. The labrum and hypopharynx have the same structure in Cyclorrhapha as in other flies; the labrum is excavated by the alimentary canal (fig. 14F, fc), which is closed by the hypopharynx below it,.

These rods are often thought of as parts of the maxillae, but they are articulated with the basal angles of the labrum, and their muscles move the proboscis. The prementum is covered posteriorly by a thecal sclerite (F, The), and is excavated anteriorly by the labial groove (LG), in which the labrum and the hypopharynx are established. In most of the non-biting Cyclorrhapha the entire proboscis may be folded against the underside of the head, or even completely retracted within the peristomal margin of the skull; in bite

The labial labella in most non-biting species are large, soft, oval lobes that can be bent upwards against the sides of the haustellum or spread flat to form a broad disc, the so-called "oral piston". When the labels thus spread out (fig. 14 B), the gap between their anterior parts is usually closed by the attachment of the lobes, except for an oval opening on its inner side, which. The canals are kept open, and their flexibility preserved, by minute rib-like thickenings of their walls, forked at one end and simply expanded at the other, leaving an open line along the exposed surfaces of the grooves, and entrance holes at their own forked limbs.

In the blow fly (B), the first 6 or 8 and the last 11 or 12 transverse canaliculi of each labellum open, respectively, into anterior and posterior longitudinal collecting ducts leading to the prestomum; the intermediate canaliculi, 12 in number, one on each side.

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HORN FLIES, STABLE FLIES, AND TSETSE FLIES

FAMILIES MUSCIDAE AND GLOSSINIDAE

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The stable flies belong to the genus Stomoxys Geoffroy, of which the species is most common in Africa, but when the haustellum is not in use, it extends horizontally from the head, but when the fly bites, the organ is said to be rotated. vertically and driven for a third or more of its length into the flesh of the victim.The structure of the proboscis of Stomoxys, including the labellar armature, has been fully described and amply illustrated by Stephens and Newstead (1907).

Horn flies settle in their thousands on the bodies of livestock, and the irritation from their incessant biting, together with blood loss, results in reduced vitality and reduced milk production. It is also a serious pest to humans, especially when it is abundant near summer resorts. Both the horn fly and the stable fly are potential carriers of livestock diseases such as anthrax and surra.

It has been claimed, from experiments on monkeys, that the horn fly is a vector of human poliomyelitis, but more recent tests (Herms, 1939) seem to give negative results. In any case, these flies illustrate well how a normally harmless organ like the insect labium can be transformed into an instrument of torture by a few anatomical changes.

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LOUSE FLIES. FAMILY HIPPOBOSCIDAE

NO. I BITING AND DISEASE-CARRYING FLIES SNODGRASS 45

Ant, antennae; Ap, labral apodeme; Br, brain; CbP, cibarial pump; dp, clypeus; fc, alimentary canal; Hphy, hypopharynx; Enter, hyoid; Li, first leg; LG,

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I DISEASE-CARRIING FLIES — SNODGRASS 49sons to believe that the resemblance of the "tick" bat to the Hip-sons to believe that the resemblance of the "tick" bat to the Hip- boscidae is due to adaptation to the same mode of life and food; I would place the Streblidae and Nycteribiidae in the Cyclorrhapha acalypterates.