Mosquitoes differ greatly in their habits. The Stegomyia and Culex breed about houses, frequently in artificial collections of water, the Anopheles in swamps and terrestrial waters only, as a rule. The flight of the latter is about half a mile, but they may be carried six miles or more by winds. They are soon killed by strong direct sunlight, and by storms. Both sexes subsist on vegetable matter, but the female of certain species requires a meal of blood from man or animals for the full development of the eggs. These insects lay their eggs on the surface of still water. In a day or two these hatch into larvae and these, in turn, in about a week or 8 days into pupae. The mature insect emerges from the pupa case in 2 or 3 days. The full period of development from the eggs to (he adult mosquito is from 9 days to 3 or (rarely) 4 weeks, depending on the species and dimate and especially the temperature. A high temperature expedites development. Some varieties of mosquitoes may live throughout the year and have been seen alive and active in Montana in January. As a rule the family is preserved in cold climates from year to year by the insects which hibernate, in bams, brush, tall grass, etc., and by the eggs and larvae of stronger species.
<Callout type="important" title="Important">Forty-nine species of Anopheles are known to transmit malaria, but some other species of this genus are unable to act as hosts.</Callout>
Some species can act as hosts only for a certain species of the Plasmodium — but can not become infected with others. The Anopheles quadrimaculatus can convey only the parasites of tertian and quartan malaria, the Anopheles crucians only that of aestivo- autumnal fever. Malaria is one of the most widespread of preventable diseases. It is particularly prevalent in the tropics where it often has a malignant form with high mortality. It has ravaged the southern states of the Union and is believed to have been the cause of the failure of early attempts at colonization in Virginia. The mosquito becomes infected by sucking the blood of persons harboring the malarial parasites. In the course of twelve days the parasites have multiplied in the wall of the insect's stomach and entered the salivary glands. They are discharged into the victim's tissues by the act of stinging and find their way into the red blood cells, where they grow and develop. The infected person usually does not develop symptoms for a week.
<Callout type="tip" title="Tip">Mosquitoes are exterminated most thoroughly and cheaply by destroying their breeding places.</Callout>
This is effected by the drainage or filling in the pools and swamps and protection or destruction of artificial collections of water in which they breed. When drainage and filling in are not practicable, oil or larvacide may be employed. Oil forms a film on the water which prevents the larvae and pupae from reaching the air, as a result of which they die in about an hour. The best oil for this purpose is an intermediate grade between the illuminating and heavier crude oils. This spreads fairly rapidly, does not cost as much nor evaporate as quickly as kerosene, and gives a visible oil film. The thicker oils do not spread as easily and are more expensive though they cost less per barrel.
<Callout type="warning" title="Warning">An oil film will not penetrate a barrier of grass or move around it.</Callout>
In many waters obstructions such as sticks and stones may interfere with its uniform spread. The quantity of oil needed for a given area can not be stated because of the obstructions that it must overcome, temperature, etc. All oils spread better in warm weather. The facility with which a given commercial quality will spread varies greatly.
Oil may be applied by several appliances, (i) A watering pot is useful for small pools. (2) A knapsack sprayer, which is operated by a pump and will throw a dirigible jet 20 feet. (3) A spraying pump installed in a small flat bottomed boat, to oil the center of lagoons, etc. (4) A drip can holding from 5 to 30 gallons for intermittent or continuous application. Usually 10 to 20 drops per minute for i foot breadth of the ditch will be enough to form a continuous film. The can is elevated 3 or 4 feet above the ditch so that the drops will break on impact. In many cases the drip need be operated continuously for only one or two days each week. On long ditches several cans should be used, at appropriate intervals.
<Callout type="important" title="Important">Though drip cans are more economical than other methods of application they tend to clog and require frequent attention.</Callout>
The flow is regulated by one of several methods. The simplest is to drive a nail surrounded by cotton into the bottom of the can. The flow is regulated by the tightness with which the nail head holds the cotton against the can. A better plan is to insert a compressible flat tube about 3 inches above the bottom of the can and inserting into this a lamp wick. Two inches of water are then placed in the can and the vessel is filled with oil. Flow of fluid is regulated by compressing the tube.
A small bundle of cotton waste, soaked in pil, is used when the quantity of water is too small to justify the use of an oil can. 'Larvacide' was used on the Panama Canal Zone for destruction of larvae where there was much aquatic vegetation. It was made as follows: One hundred and fifty gallons of crude carbolic acid containing not less than 15 per cent, of phenols were heated in an iron tank having a steam coil with steam at 50 pounds pressure; 200 pounds of finely crushed and sifted common rosin were dissolved in the boiling acid, and then 30 pounds of caustic soda dissolved in 6 gallons of water were added. There was a mechanical stirring rod attached to the mixing tank. The product was ready in a few minutes, yielding about 3½ barrels.
As a mosquito larvacide it was used by spraying an aqueous emulsion (one part of larvacide to five of water) over the surface to be treated and along the margin of pools and ponds or other mosquito-breeding places, so that the resulting dilution of the larvacide had a thin, milky opalescence representing approximately a dilution of 1 to 5000. A 1 to 1000 dilution killed the larvae more rapidly, and was used for destruction of larvae in overflowing pools, etc., and where the use of oil was not practicable.
Underbrush and high grass in which insects find refuge should be destroyed. Mosquitoes should be destroyed in the buildings in cantonments and fixed camps. This is done by a search for them with a flash light and killing them by 'swatters' or the use of a wide-mouthed bottle containing chloroform in cotton. If a dark band be painted on the wall the insects will usually light on it, and will be found very easily.
Cantonments should be screened with a net of not less than 16 strands to the inch. This should be as far as possible, of copper though 5 to 10 per cent, of zinc are permissible. A good, inexpensive screening consists of 65.75 per cent, copper, 34 per cent, zinc and i per cent. iron. The less iron the better.
In the field as a protection against malaria individual mosquito bars, head nets and gloves should be used. This is the best single prophylactic measure that is then available except the daily administration of quinine. Prevention of malaria by the use of quinine has given good results. Authorities differ in the dosage that should be used. Celli's method, using a dose of 6 grains of quinine daily has given excellent results in the Italian army. It should be given to all troops in malarious regions daily at retreat. If daily dosage is not practical 15 grains should be given every other day.
Many persons in malarious regions who appear perfectly healthy, harbor the parasites of this disease and are therefore foci of infection. The proportion of such carriers varies widely in different districts. An average of the data collected by Craig shows that about one-third of the children and one-fourth of the adults in malarious regions are carriers. These persons have at least one parasite in the blood to each 500 white blood corpuscles. They should receive 30 grains of quinine daily until the plasmodi a have disappeared from the blood, then daily doses of 15 grains for two weeks, then 10 grains daily for two weeks, then the usual prophylactic dose for at least 2 months.
Acute cases should be protected from the bites of insects by screened rooms or mosquito bars and receive systematic treatment. Yellow Fever. — Until recent years yellow fever was constantly present in Havana, Vera Cruz, Panama, and other Spanish American ports. They were foci from which epidemics spread to tropical and subtropical ports on both the Atlantic and Pacific coasts of America, as far north as Boston, to the west coast of Africa and to the southwest coast of Europe. It has been a scourge of the American continent until Major Walter Reed, U. S. A., and his collaborators demonstrated that the disease was caused by the bite of infected mosquitoes.
These officers showed that the mosquito is infected by biting a yellow fever patient during the first 3 days of the disease, and after about 12 days will convey the disease to the persons whom it bites. These then develop the disease in from 3 to 5 days, this being the period of incubation.
The yellow fever mosquito, (Culex calopus) has a wide area of distribution, ranging from 40° north latitude to about 40° south. It is found in China and Japan, the East and West Indies, the Philippines and the Hawaiian Islands. The insect breeds as a rule in artificial collections of water, is usually found near dwellings and has a short radius of flight, probably not over 75 yards. It will not travel even a short distance over water so that a vessel moored 1200 yards from shore is entirely safe from its unaided approach.
There is no natural immunity to yellow fever but an attack confers immunity which lasts throughout life. Many persons living in districts where it is endemic have mild and unrecognized attacks in childhood which give them lifelong immunity. It is these mild cases which are not recognized as yellow fever, which facilitate the spread of the disease, for they are unrecognized and are not protected from the bites of mosquitoes.
Prevention of this disease may be accomplished by: (i) the protection of all known and suspected cases from the bites of mosquitoes; (2) protection of healthy people from the bites of mosquitoes; (3) destruction of adult insects and (4) control of their breeding places. Patients should be isolated in compartments screened with a mesh of at least 18 strands to the inch. A mesh of 16 strands is usually adequate but not invariably so, as the Culex is a small mosquito.
Houses in infected localities should be protected in the same manner. As soon as a patient is removed from his room and before mosquitoes have a chance to escape it should be disinfected with sulphur dioxide 2 lb. per 1000 ft. Breeding is controlled by screening or oiling tanks, cisterns, etc., and eliminating standing water in and about households.
The prevention of yellow fever is much simpler than that of malaria, for the Culex does not fly far and its breeding habits are easily controlled. Further, a patient is infective only in the first 3 days of the disease and thereafter is immune — ^is not a carrier.
Dengue. — Dengue, or breakbone fever, is an acute disease occurring in epidemic form in tropical and subtropical countries. It is characterized by severe pains in the muscles and joints and by an eruption similar to that of measles. It rarely ends fatally, but is sometimes followed by a protracted period of debility. The disease is constantly present at the beginning of the rainy season in the Philippines. Epidemics have occurred along the Mexican border, but not in very recent years.
It is important that the disease be differentiated from yellow fever with which the early cases of an epidemic have sometimes been confounded. The cause of the disease has never been identified. It is transmitted by the Culex fatigans, a mosquito common throughout most tropical and subtropical regions, and by the Culex calopus.
Preventive measures are the destruction of the breeding places of mosquitoes, the protection of patients from their bites, screening of houses, etc. The culex mosquitoes breed at a distance from houses, as well as in their vicinity, and have a strong flight. The measures used must be carried further afield than those for destruction of the yellow fever mosquito.
Flies. — Household flies are found in practically all parts of the world, except the coldest regions. They are 99 per cent, of the flies caught in houses. In summer camps they abound, unless measures be taken to prevent their breeding. They are especially abundant in cattle and horse raising countries.
Eggs are laid preferably in horse manure, but also in human excreta, manure of pigs and other animals, decaying animal or vegetable matter, especially if soiled with excreta, kitchen refuse, etc., and polluted soil. About 120 eggs are laid at one time. Several insects usually deposit their eggs in the same spot, so that they appear in small irregular clusters, from ½ to i inch in diameter.
The eggs hatch in from 8 to 24 hours and the maggots which emerge reach their full size (about 1/3 inch long) in about 4 days. Prior to this they have kept below the surface feeding on the organic matter but now they migrate to And a suitable place for the pupal stages This is usually the edge of the manure pile, or near it on the ground.
The pupa is nearly cylindrical, from yellowish to dark brown in color. This stage lasts from 5 to 10 days. The total time from laying eggs to emergence of the adult fly is from 8 to 15 days, usually 10 days. In cold or dry weather it may be many months.
As a rule flies lay only once or twice but six or seven generations may develop during a summer. The species is perpetuated over cold weather by the impregnated females and pupae who have found shelter. Maggots scattered with manure may be destroyed by dryness.
Flies transmit disease by conveying germs on their feet or other parts of the body, by vomiting liquids from their crops or by voided intestinal contents in fly specks Each fly has about a million germs on its body but as a rule these die in a few hours. Disease carrying germs may live several days in the crops and even longer in the bowels of these insects, yet retain their full virulence when discharged.
As a fly consumes about its own weight of food daily and defecates every few minutes, its chief danger is through the fly specks it leaves. It b a common agent in the transmission of cholera, typhoid and paratypoid fever, dysentery, and other diarrheal diseases. It is also said to transmit the germs of tuberculosis, yaws, trachoma, plague, small pox, leprosy, anthrax, ophthalamia, erysipelas, tropical sore and the eggs of parasitic worms.
Frequently it is accused of transmitting diseases without adequate proof, and some authorities believe that its importance in this role has been overestimated. But that flies are important agents in the spread of a number of diseases, especially those affecting the alimentary tract is quite beyond doubt. The influence flies exert in the transmission of disease is controlled by (i) destruction of the insects breeding places, (2) destruction of adults and (3) prevention of their obtaining access to food.
The methods by which these ends are accomplished are discussed in the chapter on camps.
Diarrhea. — Diarrhea and dysentery may, in war, cause more deaths than typhoid fever. They increase in severity usually as war progresses. They caused 57.265 deaths in the federal armies during the Civil War corresponding to a yearly mortality of 17 per 1000 or one death out of every 3.5 deaths from all sickness.
Simple diarrhea may follow the use of indigestible, unwholesome or excessive food. It is prevalent among newly raised troops when cooks do not understand field cooking. Also it is caused by fermentation or putrefactive organisms. Attacks are precipitated by exposure to inclement weather, by damp soil and breathing foul air, all of which probably act by lowering bodily resistance.
It may be caused by changes from a soft to hard water, by inorganic impurities in water, such as the calcium or magnesium salts, or by diet or by bacteria. Those parasites most frequently indicted are mentioned in an earlier part of this chapter. Most epidemics of diarrhea are of an infectious character and are spread by flies.
Key Takeaways
- Destroy breeding places to control mosquitoes and flies
- Use oil or larvacide for mosquito control
- Screen buildings with fine mesh nets
- Administer quinine prophylactically in malarial regions
- Differentiate between yellow fever and dengue
Practical Tips
- Regularly inspect and clean standing water sources to prevent mosquito breeding.
- Use fly traps or sticky papers to reduce the number of flies in your living quarters.
- Wear long sleeves and pants when outdoors, especially during dusk and dawn when mosquitoes are most active.
- Store food properly to avoid attracting flies and other insects.
- Educate yourself on the signs and symptoms of malaria and yellow fever for early detection.
Warnings & Risks
- Do not use oil or larvacide in areas with aquatic vegetation without proper dilution, as it can harm beneficial organisms.
- Be cautious when using chemical treatments like quinine; follow dosage instructions carefully to avoid toxicity.
- Avoid direct sunlight and strong winds when applying oil for mosquito control, as they can kill the larvae before they mature.
- Do not rely solely on screening for protection against mosquitoes; use additional methods such as insect repellent.
Modern Application
While many of the specific techniques described in this chapter are outdated or require modern adaptations, the principles of vector control and disease prevention remain crucial. Understanding mosquito and fly behavior can help in developing effective strategies to prevent the spread of diseases like malaria, yellow fever, dengue, and diarrhea. Modern tools such as genetically modified mosquitoes and targeted insecticides have advanced significantly but the core concepts of habitat management and personal protection are still highly relevant.
Frequently Asked Questions
Q: How can I control mosquito breeding in my home?
Destroying standing water sources is key to controlling mosquitoes. Regularly clean gutters, remove old tires, and empty any containers that hold water. You can also use oil or larvacide to prevent larvae from maturing.
Q: What are the signs of malaria in humans?
Symptoms of malaria include fever, chills, sweating, headache, muscle aches, and fatigue. The disease usually develops 10-15 days after being bitten by an infected mosquito. Early detection is crucial for effective treatment.
Q: Can flies transmit diseases other than those mentioned in the chapter?
Yes, flies can spread various diseases such as cholera, typhoid fever, and dysentery. They are known to carry a wide range of pathogens on their bodies and can contaminate food and surfaces.
Q: How effective is quinine in preventing malaria?
Quinine has been used effectively as a prophylactic measure against malaria, with daily doses of 6 grains recommended by some authorities. However, it should be administered under medical supervision due to potential side effects.
Q: What are the main differences between yellow fever and dengue?
Yellow fever is caused by a virus transmitted through mosquito bites and has a longer incubation period (3-5 days) compared to dengue. Dengue, or breakbone fever, causes severe muscle and joint pain but rarely results in death.