Page:The New International Encyclopædia 1st ed. v. 14.djvu/69

MOSQUITO. 55 MOSQUITO. gler.' Its life as a rule is short, and with the great majnritj- of the species it is a true air- breather, coming to the surface of the water at fre<|unnt inten-als and extruding its respiratory tube in order to suck air into its tracheae. With at least one species (Wyeomyia Smithii) , and EQG8 AND LART.E. a. a * raft * of pgKs of the cnmtnou mosquito (culex) : b, a sinjcle larva (' wigg-Ier ') takiug breath at the surface : c, a larva (enlarged). perhaps with others, the anal locomotory flaps have an abundantly branched tracheal supply, and at least during part of the lanal life these Haps function as air-gills, rendering it possible for the larva to remain below the surface of the water for a prolonged period of time. The food of mosquito larva; is most variable. They swal- low all sorts of minute organisms which float upon the surface or are held in suspension in the water. The larvie of Anopheles feed for the greater part of their life at the surface, and con- sequently ilevour mainly the spores of alga; whi(?li float there. Later in life in shallow water they descend to the bottom and feed upon heavier objects. The larvte of Culex feed below the sur- face upon small organisms, animal and vegetable, and mineral as well, which are held in suspen- sion. The larvae of Psorophora seem largely carnivorous, and, on account of their large size, are able to overpower and to devour other mos- quito larva; and other aquatic insects. They are even cannibals, and will feed upon small indi- viduals of their own kind. All mosquito larvie are very active, wriggling quickly through the water by abrupt and rapid bendiugs of the body, aided in some cases by long lateral hairs, and especially by a well-developed group of flaps at the anal end of the body. Food is brought into the mouth by the active movement of long oral cilia. In many forms the jaws are undeveloped, hut in some, as in Psorophora, they are well formed and adapted for piercing and tearing. The pupa is also active, but does not feed, and possesses no mouth parts. As a rule it floats at the surface of the water, breathing through two respiratory tubes which issue from the thorax — a curious change from the respiratory tube of the larva, which is single and issues from the anal end of the abdomen. Although generally floating at the surface, the pupa when disturbed rapidly vanishes below the surface by energptic movements of the abdomen and of the anal flaps, and is thus enabled to a certain ex- tent to avoid the attacks of fish and other ene- mies. The pupal stage is usually of short dura- tion, and the adult issues through the cracking of the skin of the thorax. With many mosquitoes there are several generations annually. With Cnlfx pipinis and Anophelen tnnriilipriivis, for example, there may be from eight to twelve such generations in a long summer. With other spe- cies it seems reasonably certain that the life- duration of the individual is much greater, and that in some cases there may be but a single generation each year, ilost mosquitoes hibernate as adults, stowing themselves away in protected places at the beginning of cold weather. Other species und<nil)tedly hibernate in the egg stage, and still others unquestionably hibernate as larva-, readily standing extremes of temperature, and even emerging in good condition with the warm weather of spring from bloclvs of ice in which they have been solidly frozen. Agency of Mosquitoes ix C'.rkiage of Dis- ease. Since 1808 mosquitoes have become of vital importance to the human race, following the discovery that they are secondary- agents in the carriage of several diseases of human beings, notably malaria and j-ellow fever. See Insects, Propag.tiox of Disease by. Riddance of JIosquitoes. The naost effective way of relieving a neighborhood of mosquitoes consists in abolishing the breeding places. All accunmlations of stagnant water — and these are of the most varied and frequently inaccessible character — must be removed wherever it is pos- sible. Swampy lands should be drained: hollows in old trees and stumps should be filled up ; old cans and bottles should be removed; cesspools should be hermetically sealed; rain-water bar- rels should be covered with fine wire gauze; the roof-troughs of houses should be frequently cleaned out. No possible supply of standing water should be overlooked, and these will in many eases require a most careful and ingenious search. Where mosquitoes are breeding in troughs or large cement Ijasins which are used for watering stock, fish, such as sunfish, gold- fish, or top minnows (qq.v.), should be intro- duced. Where other ponds exist which it is not possible to drain, the water margins should be kept clean and .sharp, and superabundant vegeta- tion should be removed. Sloreover, if the fish supply of such ponds cannot be made satisfactory, a certain amount of kerosene placed upon the surface of the water will quickly destroy mos- quito larv.ne. This kerosening of swamp lands, where drainage is impossible or very expensive, is often a temporaiy remedy of great value. In malarial regions persons may be protected from the bite of the dangerous and annoying mosqui- toes by the careful screening of houses and by wearing mosquito veils and gloves at night when obliged to be out of doors. Anopheles, as a rule, bites only at night. By this method the Italian Government has gi-eatly reduced malaria in the black belt of Italy. By protecting healthy per- sons and malarial patients as well, and by the free use of quinine with the patients, the general health of the population of that region has greatly improved. The Germans in East Africa believe that they can wipe out malaria by sim- ply destroying the disease with medicine. Ma- laria once abolished in human beings, there will be none for the mosquitoes to carry. In the United States extensive work has been done in the destruction of breeding places and thus re- ducing the numbers of mosquitoes. I'nder such conditions malaria will die out. In Cuba, aside from protecting the early yellow-fever patients and the constant use of mosquito bars in hos- pitals, yellow fever has been exterminated by