Handbook of Medical Entomology Part 4

[Ill.u.s.tration: 23. Melanolestes abdominalis (2). After Marlatt.]

One of the most interesting of these species is _Reduvius personatus_, (= _Opsictus personatus_), which is popularly known as the "masked bed-bug hunter." It owes this name to the fact that the immature nymphs (fig. 21) have their bodies and legs completely covered by dust and lint, and that they are supposed to prey upon bed-bugs. LeConte is quoted by Howard as stating that "This species is remarkable for the intense pain caused by its bite. I do not know whether it ever willingly plunges its rostrum into any person, but when caught, or unskilfully handled it always stings. In this case the pain is almost equal to the bite of a snake, and the swelling and irritation which result from it will sometimes last for a week."

A species which very commonly attacks man is _Conorhinus sanguisugus_, the so-called "big bed-bug" of the south and southern United States. It is frequently found in houses and is known to inflict an exceedingly painful bite. As in the case of a number of other predaceous Hemiptera, the salivary glands of these forms are highly developed. The effect of the bite on their prey and, as Marlatt has pointed out, the constant and uniform character of the symptoms in nearly all cases of bites in man, clearly indicate that their saliva contains a specific substance. No satisfactory studies of the secretions have been made. On the other hand, Dr. Howard is doubtless right in maintaining that the very serious results which sometimes follow the bite are due to the introduction of extraneous poison germs. This is borne out by the symptoms of most of the cases cited in literature and also by the fact that treatment with corrosive sublimate, locally applied to the wound, has yielded favorable results.

OTHER HEMIPTERA REPORTED AS POISONOUS TO MAN--A large number of other Hemiptera have been reported as attacking man. Of these, there are several species of Lygaeidae, Coreidae, and Capsidae. Of the latter, _Lygus pratensis_, the tarnished plant-bug, is reported by Professor Crosby as sucking blood. _Orthotylus flavosparsus_ is another Capsid which has been implicated. _Empoasca mali_ and _Platymetopius acutus_ of the Ja.s.sidae have also been reported as having similar habits.

Whenever the periodical cicada or "seventeen-year locust" becomes abundant, the newspapers contain accounts of serious results from its bites. The senior author has made scores of attempts to induce this species to bite and only once successfully. At that time the bite was in no wise more severe than a pin-p.r.i.c.k. A student in our department reports a similar experience. There is no case on record which bears evidence of being worthy of any credence, whatsoever.

Under the heading of poisonous Hemiptera we might consider the bed-bugs and the lice. These will be discussed later, as parasites and as carriers of disease, and therefore need only be mentioned here.

DIPTERA

Several species of blood-sucking Diptera undoubtedly secrete a saliva possessing poisonous properties. Chief among these are the Culicidae, or mosquitoes, and the Simuliidae, or black-flies. As we shall consider these forms in detail under the heading of parasitic species and insects transmitting disease, we shall discuss here only the poison of the mosquitoes.

It is well known that mosquitoes, when they bite, inject into the wound a minute quant.i.ty of poison. The effect of this varies according to the species of mosquito and also depends very much on the susceptibility of the individual. Soon after the bite a sensation of itching is noticed and often a wheal, or eminence, is produced on the skin, which may increase to a considerable swelling. The scratching which is induced may cause a secondary infection and thus lead to serious results. Some people seem to acquire an immunity against the poison.

The purpose of this irritating fluid may be, as Reaumur suggested, to prevent the coagulation of the blood and thus not only to cause it to flow freely when the insect bites but to prevent its rapid coagulation in the stomach. Obviously, it is not developed as a protective fluid, and its presence subjects the group to the additional handicap of the vengeance of man.

[Ill.u.s.tration: 24. Diagram of a longitudinal section of a mosquito.]

As to the origin of the poison, there has been little question, until recent years, that it was a secretion from the salivary glands.

Macloskie (1888) showed that each gland is subdivided into three lobes, the middle of which differs from the others in having evenly granulated contents and staining more deeply than the others (fig. 24). This middle lobe he regarded as the source of the poison. Bruck, (1911), by the use of water, glycerine, chloroform, and other fluids, extracted from the bodies of a large number of mosquitoes a toxine which he calls _culicin_. This he a.s.sumes comes from the salivary glands. Animal experimentation showed that this extract possessed hemolytic powers.

Inoculated into the experimenter's own skin it produced lesions which behaved exactly as do those of mosquito bites.

Similarly, most writers on the subject have concurred with the view that the salivary glands are the source of the poison. However, recent work, especially that of Nuttall and Shipley (1903), and Schaudinn (1904), has shown that the evidence is by no means conclusive. Nuttall dissected out six sets (thirty-six acini) of glands from freshly killed _Culex pipiens_ and placed them in a drop of salt solution. The drop was allowed to dry, it being thought that the salt crystals would facilitate the grinding up of the glands with the end of a small gla.s.s rod, this being done under microscopic control. After grinding up, a small drop of water was added of the size of the original drop of saline, and an equal volume of human blood taken from the clean finger-tip was quickly mixed therewith, and the whole drawn up into a capillary tube. Clotting was not prevented and no hemolysis occurred. Salivary gland emulsion added to a dilute suspension of corpuscles did not lead to hemolysis. This experiment was repeated a number of times, with slight modification, but with similar results. The data obtained from the series "do not support the hypothesis that the salivary glands, at any rate in _Culex pipiens_, contain a substance which prevents coagulation."

Much more detailed, and the more important experiments made along this line, are those of Schaudinn (1904). The results of these experiments were published in connection with a technical paper on the alternation of generations and of hosts in _Trypanosoma_ and _Spirochaeta_, and for this reason seem to have largely escaped the notice of entomologists.

They are so suggestive that we shall refer to them in some detail.

Schaudinn observed that the three sophageal diverticula (commonly, but incorrectly, known as the "sucking stomach") (fig. 24) usually contain large bubbles of gas and in addition, he always found yeast cells. On the ground of numerous observations, Schaudinn was convinced that these yeast plants are normal and constant commensals of the insect. He regarded them as the cause of the gas bubbles to be found in diverticula. It was found that as the insect fed, from time to time the abdomen underwent convulsive contractions which resulted in the emptying of the sophageal diverticula and the salivary glands through blood pressure.

In order to test the supposed toxic action of the salivary glands, Schaudinn repeatedly introduced them under his skin and that of his a.s.sistant, in a drop of salt solution, and never obtained a suggestion of the irritation following a bite of the insect, even though the glands were carefully rubbed to fragments after their implantation. Like Nuttall, he failed to get satisfactory evidence that the secretion of the salivary glands r.e.t.a.r.ded coagulation of the blood.

He then carefully removed the sophageal diverticula with their content of yeast and introduced them into an opening in the skin of the hand. Within a few seconds there was noticeable the characteristic itching irritation of the mosquito bite; and in a short time there appeared reddening and typical swelling. This was usually much more severe than after the usual mosquito bite, and the swelling persisted and itched longer. This was because by the ordinary bite of the mosquito most of the yeast cells are again sucked up, while in these experiments they remained in the wound. These experiments were repeated a number of times on himself, his a.s.sistant and others, and always with the same result. From them Schaudinn decided that the poisonous action of the mosquito bite is caused by an enzyme from a commensal fungus. These conclusions have not, as yet, been satisfactorily tested.

Relief from the effect of the mosquito bite may be obtained by bathing the swellings with weak ammonia or, according to Howard, by using moist soap. The latter is to be rubbed gently on the puncture and is said to speedily allay the irritation. Howard also quotes from the _Journal of Tropical Medicine and Hygiene_ to the effect that a few drops of a solution of thirty to forty grains of iodine to an ounce of saponated petroleum rubbed into the mosquito bite, or wasp sting, allay the pain instantaneously.

Methods of mosquito control will be discussed later, in considering these insects as parasites and as carriers of disease.

STINGING INSECTS

The stinging insects all belong to the order HYMENOPTERA. In a number of families of this group the ovipositor is modified to form a sting and is connected with poison-secreting glands. We shall consider the apparatus of the honey-bee and then make briefer reference to that of other forms.

APIS MELLIFICA, THE HONEY BEE--The sting of the worker honey-bee is situated within a so-called sting chamber at the end of the abdomen.

This chamber is produced by the infolding of the greatly reduced and modified eighth, ninth and tenth abdominal segments into the seventh.[D]

From it the dart-like sting can be quickly exserted.

The sting (fig. 25) is made up of a central shaft, ventro-laterad of which are the paired _lancets_, or darts, which are provided with sharp, recurved teeth. Still further laterad lie the paired whitish, finger-like _sting palpi_. Comparative morphological as well as embryological studies have clearly established that these three parts correspond to the three pairs of gonopophyses of the ovipositor of more generalized insects.

[Ill.u.s.tration: 25. Sting of a honey bee. _Psn Sc_, base of acid poison gland; _B Gl_, alkaline poison gland; _Stn Plp_, sting palpi; _Sh B_, bulb of sting; _Sh A_, basal arm; _Lct_, lancets or darts; _Sh s_, shaft of sting. Modified from Snodgra.s.s.]

[Ill.u.s.tration: 26. Poison apparatus of a honey bee. Modified from Snodgra.s.s.]

An examination of the internal structures (fig. 26) reveals two distinct types of poison glands, the acid-secreting and the alkaline-secreting glands, and a prominent poison reservoir. In addition, there is a small pair of accessory structures which have been called lubricating glands, on account of the supposed function of their product. The acid-secreting gland empties into the distal end of the poison reservoir which in turn pours the secretion into the muscular bulb-like enlargement at the base of the shaft. The alkaline secreting gland empties into the bulb ventrad of the narrow neck of the reservoir.

The poison is usually referred to as formic acid. That it is not so easily explained has been repeatedly shown and is evidenced by the presence of the two types of glands. Carlet maintains that the product of either gland is in itself innocent,--it is only when they are combined that the toxic properties appear.

The most detailed study of the poison of the honey-bee is that of Josef Langer (1897), who in the course of his work used some 25,000 bees.

Various methods of obtaining the active poison for experimental purposes were used. For obtaining the pure secretion, bees were held in the fingers and compressed until the sting was exserted, when a clear drop of the poison was visible at its tip. This was then taken up in a capillary tube or dilute solutions obtained by dipping the tip of the sting into a definite amount of distilled water.

An aqueous solution of the poison was more readily obtained by pulling out the sting and poison sacs by means of forceps, and grinding them up in water. The somewhat clouded fluid was then filtered one or more times. For obtaining still greater quant.i.ties, advantage was taken of the fact that while alcohol coagulates the poison, the active principle remains soluble in water. Hence the stings with the annexed glands where collected in 96 per cent alcohol, after filtering off of the alcohol were dried at 40 C., then rubbed to a fine powder and this was repeatedly extracted with water. Through filtering of this aqueous extract there was obtained a yellowish-brown fluid which produced the typical reactions, according to concentration of the poison.

The freshly expelled drop of poison is limpid, of distinct acid reaction, tastes bitter and has a delicate aromatic odor. On evaporation, it leaves a sticky residue, which at 100 degrees becomes fissured, and suggests dried gum arabic. The poison is readily soluble in water and possesses a specific gravity of 1.1313. On drying at room temperature, it leaves a residue of 30 per cent, which has not lost in poisonous action or in solubility. In spite of extended experiments, Langer was unable to determine the nature of the active principle. He showed that it was not, as had been supposed, an alb.u.minous body, but rather an organic base.

The pure poison, or the two per cent aqueous solution, placed on the uninjured skin showed absolutely no irritating effect, though it produced a marked reaction on the mucus membrane of the nose or eye. A single drop of one-tenth per cent aqueous solution of the poison brought about a typical irritation in the conjunctiva of the rabbit's eye. On the other hand, the application of a drop of the poison, or its solution, to the slightest break in the skin, or by means of a needle piercing the skin, produced typical effects. There is produced a local necrosis, in the neighborhood of which there is infiltration of lymphocytes, dema, and hyperaemia.

The effect of the sting on man (fig. 27) is usually transitory but there are some individuals who are made sick for hours, by a single sting.

Much depends, too, on the place struck. It is a common experience that an angry bee will attempt to reach the eye of its victim and a sting on the lid may result in severe and prolonged swelling. In the case of a man stung on the cheek, Legiehn observed complete aphonia and a breaking out of red blotches all over the body. A sting on the tongue has been known to cause such collateral dema as to endanger life through suffocation. Cases of death of man from the attacks of bees are rare but are not unknown. Such results are usually from a number of stings but, rarely, death has been known to follow a single sting, entering a blood vessel of a particularly susceptible individual.

[Ill.u.s.tration: Effect of bee stings. After Root.]

It is clearly established that partial immunity from the effects of the poison may be acquired. By repeated injections of the venom, mice have been rendered capable of bearing doses that certainly would have killed them at first. It is a well-known fact that most bee-keepers become gradually hardened to the stings, so that the irritation and the swelling become less and less. Some individuals have found this immunity a temporary one, to be reacquired each season. A striking case of acquired immunity is related by the Roots in their "A B C and X Y Z of Bee Culture." The evidence in the case is so clear that it should be made more widely available and hence we quote it here.

A young man who was determined to become a bee-keeper, was so susceptible to the poison that he was most seriously affected by a single sting, his body breaking out with red blotches, breathing growing difficult, and his heart action being painfully accelerated. "We finally suggested taking a live bee and pressing it on the back of his hand until it merely pierced his skin with the sting, then immediately brushing off both bee and sting. This was done and since no serious effect followed, it was repeated inside of four or five days. This was continued for some three or four weeks, when the patient began to have a sort of itching sensation all over his body. The hypodermic injections of bee-sting poison were then discontinued. At the end of a month they were repeated at intervals of four or five days. Again, after two or three weeks the itching sensation came on, but it was less p.r.o.nounced.

The patient was given a rest of about a month, when the doses were repeated as before." By this course of treatment the young man became so thoroughly immunized that neither unpleasant results nor swelling followed the attacks of the insects and he is able to handle bees with the same freedom that any experienced bee-keeper does.

In an interesting article in the _Entomological News_ for November, 1914, J. H. Lovell calls attention to the fact that "There has been a widespread belief among apiarists that a beekeeper will receive more stings when dressed in black than when wearing white clothing. A large amount of evidence has been published in the various bee journals showing beyond question that honey-bees under certain conditions discriminate against black. A few instances may be cited in ill.u.s.tration. Of a flock of twelve chickens running in a bee-yard seven black ones were stung to death, while five light colored ones escaped uninjured. A white dog ran among the bee-hives without attracting much attention, while at the same time a black dog was furiously a.s.sailed by the bees. Mr. J. D. Byer, a prominent Canadian beekeeper, relates that a black and white cow, tethered about forty feet from an apiary, was one afternoon attacked and badly stung by bees. On examination it was found that the black spots had five or six stings to one on the white. All noticed this fact, although no one was able to offer any explanation. A white horse is in much less danger of being stung, when driven near an apiary, than a black one. It has, indeed, been observed repeatedly that domestic animals of all kinds, if wholly or partially black, are much more liable to be attacked by bees, if they wander among the hives, than those which are entirely white."

In order to test the matter experimentally, the following series of experiments was performed. In the language of the investigator:

"On a clear, warm day in August I dressed wholly in white with the exception of a black veil. Midway on the sleeve of my right arm there was sewed a band of black cloth ten inches wide. I then entered the bee-yard and, removing the cover from one of the hives, lifted a piece of comb with both hands and gently shook it. Instantly many of the bees flew to the black band, which they continued to attack as long as they were disturbed. Not a single bee attempted to sting the left sleeve, which was of course entirely white, and very few even alighted upon it."

"This experiment was repeated a second, third and fourth time; in each instance with similar results. I estimated the number of bees on the band of black cloth at various moments was from thirty to forty; it was evident from their behavior that they were extremely irritable. To the left white sleeve and other portions of my clothing they paid very little attention; but the black veil was very frequently attacked."

"A few days later the experiments were repeated, but the band of black cloth, ten inches wide, was sewed around my left arm instead of around the right arm as before. When the bees were disturbed, after the hive cover had been removed, they fiercely attacked the band of black cloth as in the previous experiences; but the right white sleeve and the white suit were scarcely noticed. At one time a part of the black cloth was almost literally covered with furiously stinging bees, and the black veil was a.s.sailed by hundreds. The bees behaved in a similar manner when a second hive on the opposite side of the apiary was opened."

"A white veil which had been procured for this purpose, was next subst.i.tuted for the black veil. The result was most surprising, for, whereas in the previous experiments hundreds of bees had attacked the black veil, so few flew against the white veil as to cause me no inconvenience. Undoubtedly beekeepers will find it greatly to their advantage to wear white clothing when working among their colonies of bees and manipulating the frames of the hives."

When a honey-bee stings, the tip of the abdomen, with the entire sting apparatus, is torn off and remains in the wound. Here the muscles continue to contract, for some minutes, forcing the barbs deeper and deeper into the skin, and forcing out additional poison from the reservoir.

Treatment, therefore, first consists in removing the sting without squeezing out additional poison. This is accomplished by lifting and sc.r.a.ping it out with a knife-blade or the fingernail instead of grasping and pulling it out. Local application of alkalines, such as weak ammonia, are often recommended on the a.s.sumption that the poison is an acid to be neutralized on this manner, but these are of little or no avail. They should certainly not be rubbed in, as that would only accelerate the absorption of the poison. The use of cloths wrung out in hot water and applied as hot as can be borne, affords much relief in the case of severe stings. The application of wet clay, or of the end of a freshly cut potato is sometimes helpful.

In extreme cases, where there is great susceptibility, or where there may have been many stings, a physician should be called. He may find strychnine injections or other treatment necessary, if general symptoms develop.