Handbook of Medical Entomology Part 10

The adults are remarkable for their longevity, a factor which is of importance in considering the spread of the insect and methods of control. Dufour (1833) (not De Geer, as often stated) kept specimens for a year, in a closed vial, without food. This ability, coupled with their willingness to feed upon mice, bats, and other small mammals, and even upon birds, accounts for the long periods that deserted houses and camps may remain infested. There is no evidence that under such conditions they are able to subsist on the starch of the wall paper, juices of moistened wood, or the moisture in the acc.u.mulations of dust, as is often stated.

There are three or four generations a year, as Girault's breeding experiments have conclusively shown. He found that the bed-bug does not hibernate where the conditions are such as to allow it to breed and that breeding is continuous unless interrupted by the lack of food or, during the winter, by low temperature.

Bed-bugs ordinarily crawl from their hiding places and attack the face and neck or uncovered parts of the legs and arms of their victims. If undisturbed, they will feed to repletion. We have found that the young nymph would glut itself in about six minutes, though some individuals fed continuously for nine minutes, while the adult required ten to fifteen minutes for a full meal. When gorged, it quickly retreats to a crack or crevice to digest its meal, a process which requires two or three days. The effect of the bite depends very greatly on the susceptibility of the individual attacked. Some persons are so little affected that they may be wholly ignorant of the presence of a large number of bugs. Usually the bite produces a small hard swelling, or wheal, whitish in color. It may even be accompanied by an edema and a disagreeable inflammation, and in such susceptible individuals the restlessness and loss of sleep due to the presence of the insects may be a matter of considerable importance. Stiles (1907) records the case of a young man who underwent treatment for neurasthenia, the diagnosis being agreed upon by several prominent physicians; all symptoms promptly disappeared, however, immediately following a thorough fumigation of his rooms, where nearly a pint of bed-bugs were collected.

It is natural to suppose that an insect which throughout its whole life is in such intimate relations.h.i.+p with man should play an important role in the transmission of disease. Yet comparatively little is definitely known regarding the importance of the bed-bug in this respect. It has been shown that it is capable of transmitting the bubonic plague, and South American trypanosomiasis. Nuttall succeeded in transmitting European relapsing fever from mouse to mouse by its bite. It has been claimed that Oriental sore, tuberculosis, and even syphilis may be so carried. These phases of the subject will be considered later.

The sources of infestation are many, and the invasion of a house is not necessarily due to neglect, though the continued presence of the pests is quite another matter. In apartments and closely placed houses they are known to invade new quarters by migration. They are frequently to be met with in boat and sleeper berths, and even the plush seats of day coaches, whence a nucleus may be carried in baggage to residences. They may be brought in the laundry or in clothes of servants.

Usually they are a great scourge in frontier settlements and it is generally believed that they live in nature under the bark of trees, in lumber, and under similar conditions. This belief is founded upon the common occurrence of bugs resembling the bed-bug, in such places. As a matter of fact, they are no relation to bed-bugs but belong to plant-feeding forms alone (fig. 19 _c_, _d_).

It is also often stated that bed-bugs live in poultry houses, in swallows nests, and on bats, and that it is from these sources that they gain access to dwellings. These bugs are specifically distinct from the true bed-bug, but any of them may, rarely, invade houses. Moreover, chicken houses are sometimes thoroughly infested with the true _Cimex lectularius_.

Control measures consist in the use of iron bedsteads and the reduction of hiding places for the bugs. If the infestation is slight they may be exterminated by a vigilant and systematic hunt, and by squirting gasoline or alcohol into cracks and crevices of the beds, and furniture.

Fumigation must be resorted to in more general infestations.

The simplest and safest method of fumigation is by the use of flowers of sulphur at the rate of two pounds to each one thousand cubic feet of room s.p.a.ce. The sulphur should be placed in a pan, a well made in the top of the pile and a little alcohol poured in, to facilitate burning.

The whole should be placed in a larger pan and surrounded by water so as to avoid all danger of fire. Windows should be tightly closed, beds, closets and drawers opened, and bedding spread out over chairs in order to expose them fully to the fumes. As metal is tarnished by the sulphur fumes, ornaments, clocks, instruments, and the like should be removed.

When all is ready the sulphur should be fired, the room tightly closed and left for twelve to twenty-four hours. Still more efficient in large houses, or where many hiding places favor the bugs, is fumigation with hydrocyanic acid gas. This is a deadly poison and must be used under rigid precautions. Through the courtesy of Professor Herrick, who has had much experience with this method, we give in the Appendix, the clear and detailed directions taken from his bulletin on "Household Insects."

Fumigation with formaldehyde gas, either from the liquid or "solid"

formalin, so efficient in the case of contagious diseases, is useless against bed-bugs and most other insects.

OTHER BED-BUGS--_Cimex hemipterus_ (= _C. rotundatus_) is a tropical and subtropical species, occurring in both the old and new world. Patton and Cragg state that it is distributed throughout India, Burma, a.s.sam, the Malay Peninsula, Aden, the Island of Mauritius, Reunion, St. Vincent and Porto Rico. "It is widely distributed in Africa, and is probably the common species a.s.sociated there with man." Brumpt also records it for Cuba, the Antilles, Brazil, and Venezuela.

This species, which is sometimes called the Indian bed-bug, differs from _C. lectularius_ in being darker and in having a more elongate abdomen.

The head also is shorter and narrower, and the prothorax has rounded borders.

It has the same habits and practically the same life cycle as _Cimex lectularius_. Mackie, in India, has found that it is capable of transmitting the Asiatic type of recurrent fever. Roger suggested that it was also capable of transmitting Kala-azar and Patton has described in detail the developmental stages of _Leishmania_, the causative organism of Kala-azar, in the stomach of this bug, but Brumpt declares that the forms described are those of a common, non-pathogenic flagellate to be found in the bug, and have nothing to do with the human disease. Brumpt has shown experimentally that _Cimex hemipterus_ may transmit _Trypanosoma cruzi_ in its excrement.

_Cimex boueti_, occurring in French Guinea, is another species attacking man. Its habits and general life history are the same as for the above species. It is 3 to 4.5 mm. in length, has vestigial elytra, and much elongated antennae and legs. The extended hind legs are about as long as the body.

_Cimex columbarius_, a widely distributed species normally living in poultry houses and dove cotes, _C. inodorus_, infesting poultry in Mexico, _C. hirundinis_, occurring in the nests of swallows in Europe and _Oeciacus vicarius_ (fig. 19i) occurring in swallows' nests in this country, are species which occasionally infest houses and attack man.

[Ill.u.s.tration: 71. Conorhinus sanguisugus.]

_Conorhinus sanguisugus_, the cone-nosed bed-bug. We have seen in our consideration of poisonous insects, that various species of Reduviid bugs readily attack man. Certain of these are nocturnal and are so commonly found in houses that they have gained the name, of "big bed-bugs." The most noted of these, in the United States, is _Conorhinus sanguisugus_ (fig. 71), which is widely distributed in our Southern States.

Like its near relatives, _Conorhinus sanguisugus_ is carnivorous in habit and feeds upon insects as well as upon mammalian and human blood.

It is reported as often occurring in poultry houses and as attacking horses in barns. The life history has been worked out in considerable detail by Marlatt, (1902), from whose account we extract the following.

[Ill.u.s.tration: 72. Beak of Conorhinus sanguisugus. After Marlatt.]

The eggs are white, changing to yellow and pink before hatching. The young hatch within twenty days and there are four nymphal stages. In all these stages the insect is active and predaceous, the mouth-parts (fig.

72) being powerfully developed. The eggs are normally deposited, and the early stages are undoubtedly pa.s.sed, out of doors, the food of the immature forms being other insects. Immature specimens are rarely found indoors. It winters both in the partly grown and adult stage, often under the bark of trees or in any similar protection, and only in its nocturnal spring and early summer flights does it attack men. Marlatt states that this insect seems to be decidedly on the increase in the region which it particularly infests,--the plains region from Texas northward and westward. In California a closely related species of similar habits is known locally as the "monitor bug."

The effect of the bite of the giant bed-bug on man is often very severe, a poisonous saliva apparently being injected into the wound. We have discussed this phase of the subject more fully under the head of poisonous insects.

_Conorhinus megistus_ is a Brazilian species very commonly attacking man, and of special interest since Chagas has shown that it is the carrier of a trypanosomiasis of man. Its habits and life history have been studied in detail by Neiva, (1910).

This species is now pre-eminently a household insect, depositing its eggs in cracks and crevices in houses, though this is a relatively recent adaptation. The nymphs emerge in from twenty to forty days, depending upon the temperature. There are five nymphal stages, and as in the case of true bed-bugs, the duration of these is very greatly influenced by the availability of food and by temperature. Neiva reckons the entire life cycle, from egg to egg, as requiring a minimum of three hundred and twenty-four days.

The nymphs begin to suck blood in three to five days after hatching.

They usually feed at night and in the dark, attacking especially the face of sleeping individuals. The bite occasions but little pain. The immature insects live in cracks and crevices in houses and invade the beds which are in contact with walls, but the adults are active flyers and attack people sleeping in hammocks. The males as well as the females are blood suckers.

Like many blood-sucking forms, _Conorhinus megistus_ can endure for long periods without food. Neiva received a female specimen which had been for fifty-seven days alive in a tightly closed box. They rarely feed on two consecutive days, even on small quant.i.ties of blood, and were never seen to feed on three consecutive days.

Methods of control consist in screening against the adult bugs, and the elimination of crevices and such hiding places of the nymphs. Where the infestation is considerable, fumigation with sulphur is advisable.

PARASITIC DIPTERA OR FLIES

Of the DIPTERA or two-winged flies, many species occasionally attack man. Of these, a few are outstanding pests, many of them may also serve to disseminate disease, a phase of our subject which will be considered later. We shall now consider the most important of the group from the viewpoint of their direct attacks on man.

Psychodidae or Moth-Flies

The PSYCHODIDae or Moth-flies, include a few species which attack man, and at least one species, _Phlebotomus papatasii_, is known to transmit the so-called "three-day fever" of man. Another species is supposed to be the vector of Peruvian verruga.

The family is made up of small, sometimes very small, nematocerous Diptera, which are densely covered with hairs, giving them a moth-like appearance. The wings are relatively large, oval or lanceolate in shape, and when at rest are held in a sloping manner over the abdomen, or are held horizontally in such a way as to give the insect a triangular outline. Not only is the moth-like appearance characteristic, but the venation of the wings (fig. 163, d) is very peculiar and, according to Comstock, presents an extremely generalized form. All of the longitudinal veins separate near the base of the wing except veins R_2 and R_3 and veins M_1 and M_2. Cross veins are wanting in most cases.

Comparatively little is known regarding the life-history and habits of the Psychodidae, but one genus, _Phlebotomus_, contains minute, blood-sucking species, commonly known as sand-flies. The family is divided into two subfamilies, the PSYCHODINae and the PHLEBOTOMINae. The second of these, the PHLEBOTOMINae, is of interest to us.

THE PHLEBOTOMINae--The Phlebotominae differ from the Psychodinae in that the radical sector branches well out into the wing rather than at the base of the wing. They are usually less hairy than the Psychodinae. The ovipositor is hidden and less strongly chitinized. The species attacking man belong to the genus _Phlebotomus_, small forms with relatively large, hairy wings which are held upright, and with elongate proboscis.

The mandibles and maxillae are serrated and fitted for biting.

According to Miss Summers (1913) there are twenty-nine known species of the genus _Phlebotomus_, five European, eleven Asiatic, seven African and six American. One species only, _Phlebotomus vexator_, has been reported for the United States. This was described by Coquillett, (1907), from species taken on Plummer's Island, Maryland. It measures only 1.5 mm. in length. As it is very probable that this species is much more widely distributed, and that other species of these minute flies will be found to occur in our fauna, we quote Coquillett's description.

_Phlebotomus vexator_, Coq.: Yellow, the mesonotum brown, hairs chiefly brown; legs in certain lights appear brown, but are covered with a white tomentum; wings hyaline, unmarked; the first vein (R_1) terminates opposite one-fifth of the length of the first submarginal cell (cell R_2); this cell is slightly over twice as long as its petiole; terminal, h.o.r.n.y portion of male claspers slender, bearing many long hairs; the apex terminated by two curved spines which are more than one-half as long as the preceding part, and just in front of these are two similar spines, while near the middle of the length of this portion is a fifth spine similar to the others. Length 1.5 mm.

The life-history of the Phlebotomus flies has been best worked out for the European _Phlebotomus papatasii_ and we shall briefly summarize the account of Drr and Russ (1913) based primarily on work on this species. The European Phlebotomus flies appear at the beginning of the warm season, a few weeks after the cessation of the heavy rains and storms of springtime. They gradually become more abundant until they reach their first maximum, which in Italy is near the end of July (Gra.s.si). They then become scarcer but reach a second maximum in September. At the beginning of winter they vanish completely, hibernating individuals not being found.

After fertilization there is a period of eight to ten days before oviposition. The eggs are then deposited, the majority in a single ma.s.s covered by a slimy secretion from the sebaceous glands. The larvae emerge in fourteen to twenty days. There is uncertainty as to the length of larval life, specimens kept in captivity remaining fifty or more days without transforming. Growth may be much more rapid in nature. The larvae do not live in fluid media but in moist detritus in dark places. Marett believes that they live chiefly on the excrement of pill-bugs (Oniscidae) and lizards. Pupation always occurs during the night. The remnants of the larval skin remain attached to the last two segments of the quiescent pupa and serve to attach it to the stone on which it lives.

The pupal stage lasts eleven to sixteen days, the adult escaping at night.

Only the females suck blood. They attack not only man but all warm-blooded animals and, according to recent workers, also cold-blooded forms, such as frogs, lizards, and larvae. Indeed, Townsend (1914) believes that there is an intimate relation between _Phlebotomus_ and lizards, or other reptiles the world over. The Phlebotomus pa.s.ses the daylight hours within the darkened recesses of the loose stone walls and piles of rock in order to escape wind and strong light. Lizards inhabit the same places, and the flies, always ready to suck blood in the absence of light and wind, have been found more p.r.o.ne to suck reptilian than mammalian blood.

On hot summer nights, when the wind is not stirring, the Phlebotomus flies, or sand-flies, as they are popularly called, invade houses and sleeping rooms in swarms and attack the inmates. As soon as light begins to break the flies either escape to the breeding places, or cool, dark places protected from the wind, or a part of them remain in the rooms, hiding behind pictures, under garments, and in similar places. Wherever the Phlebotomus flies occur they are an intolerable nuisance. On account of their small size they can easily pa.s.s through the meshes of ordinary screens and mosquito curtains. They attack silently and inflict a very painful, stinging bite, followed by itching. The ankles, dorsum of the feet, wrists, inner elbow, knee joint and similar places are favorite places of attack, possibly on account of their more delicate skin.

Special interest has been attracted to these little pests in recent years, since it has been shown that they transmit the European "pappatici fever" or "three day fever." More recently yet, it appears that they are the carriers of the virus of the Peruvian "verruga." This phase of the subject will be discussed later.

Control measures have not been worked out. As Newstead says, "In consideration of the facts which have so far been brought to light regarding the economy of Phlebotomus, it is clearly evident that the task of suppressing these insects is an almost insurmountable one. Had we to deal with insects as large and as accessible as mosquitoes, the adoption of prophylactic measures would be comparatively easy, but owing to the extremely minute size and almost flea-like habits of the adult insects, and the enormous area over which the breeding-places may occur, we are faced with a problem which is most difficult of solution." For these reasons, Newstead considers that the only really prophylactic measures which can at present be taken, are those which are considered as precautionary against the bites of the insects.

Of repellents, he cites as one of the best a salve composed of the following:

Ol. Anisi 3 grs.