HEALTH NOTES

Nelson Evening Mail, Volume LXI, 5 December 1927, Page 7

HEALTH NOTES

MOSQUITOES

LIFE HISTORY AND CONTROL (Contributed by the Department of Health) Mosquitoes inhabit every country in the world —from the barren polar circle to the coral strands of India. The mosquito is also an unusually beautiful insect. This fact, however, has been concealed from the public, partly owing to the diminutive size of the insects and more especially because of their irritating bite which causes the victims to kill at sight rather than examine their ethereal beauty or their fascinating evolutions in the air. For centuries it has been realised that the most serious difficulties in the development of the tropics are the diseases peculiar thereto. Not till early in the present century was it shown that mosquitoes arc the means of spread of certain of these serious ilia. Of these it is definitely proved that malaria and dengue fever arc carried by certain mosquitoes. The story of the Panama Canal is the conquest of the mosquito. In Palestine also, thanks largely to the anti-malaria work of the medical corps, Allcnby was victorious; other campaigns, as that under Napoleon and in early periods, had failed, because malaria had so ravished the troops that the army could not hold on all the year round and had to retire before the warm season. The yellow fever of South America i 3 also mosquito borne. Doubt has existed as to tlie role of the mosquito in the African type of yellow fever. In an attempt to solve the problem, Dr. Adrian Stokes, one of the most brilliant workers in medical science in this generation, recently lost his life from yellow fever in West Africa. It is thought that lie probably became infected from the bite of one of/Ms own experimentally infected mosquitoes.

New Zealand is indeed fortunate that these diseases arc, not prevalent here; the particular types of mosquito which convey these troubles have not been proved to exist in the Dominion. Nevertheless, mosquitoes are always nuisances, and the annoyance they cause is in itself sufficient reason for measures towards their suppression. Heavy as is the indictment agaiust mosquitoes, there is perhaps one item on the credit side—it is said of one species of flic family that its fondness for the naked knees of the Highlander has given us the "Highland Fling."

LIFE HISTORY

There arc four distinct stages—(l) The female, lays one hundred or more. eggs in one batch, the eggs are minute blackish bodies usually laid on the surface of still or stagnant water. The common rain barrel type, and also many others, glue their eggs into rafts which look like flakes of soot. The burden of the cry of the female mosquito is "give us blood." Before it can lay eggs a meal of blood is necessary. (-2) In one to three days the eggs hatch into larvae. These arc the "wrigglers" from their habit of wriggling through the water 'with quick ierkv move-Kent:;. They mutt ketp ceasing to the :urf'ace t.o breathe. This

is effected through a brcathiDg tube located at the tail end. Their food cousists of minute particles of vegetable or animal matter. (3) In about a week, if the weather is warm, the wriggler casts its skin and turns into a commashaped body called the "pupa" or "nymph." The pupa takes no food, but like the wriggler comes to the surface to breathe. Its breathing organs this time are situated close to the head. (4) After two to five more days the skins of the pupa, split open "and the winged mosquitoes emerge to the surface of the water and fly away. Male mosquitoes arc vegetarians; it is ouly the female that bites. When she bites she injects into the victim a fluid from her salivary glands through a tube-like arrangement. In this fluid arc sometimes the organisms which produce malaria. To quote Shipley: "Down tlu's minute microscopic groove has flowed the fluid which has closed the continent of Africa for countless centuries to civilisation, which has played a dominating part in destroying civilisation of Ancient Greece and Ronic.

BREEDING-PLACES.

No body of water is too small for a mosquito nursery. They breed in puddles by the roadsido; in. old tins, bottles, ffre-buckets, choked roof gutters, flower-pots, tubs, etc.; in cesspools, drainage, sumps, swamps, pools, slowflowing and weedy streams, rivdr estuaries; in fact, anywhere where water is allowed to stand. In New Zealand the larvae have been found in rain water, in holes in the trunks of tfees, and dead tree-ferns, and at the.bases of the leaves of broadleaf plants; in crevasses and depressions of volcanic areas, and along the coastline in semi-saline or brackish pools of water. Large sheets of water, lagoons, and rivers are unsuitable, although they may be found in adjoining potholes and puddles. A certain number of adults survive the winter. In Auckland City adults, larvae, and pupae have been found in wet cellars in mid-winter. Bushes, etc.. afford shelter but not breedinggrounds.

PREVENTIVE AND CONTROL MEASURES

Th control of the mosquito is largely the control of breeding-places. The best results are obtained by communal elforts, but individual efforts are of great , importance. Certain natural enemies are of' service; fish are very effective. The margins of pools, streams, etc., should be kept free of vegetation to allow the lish access; ornamental ponds may be stocked with goldfish or minnows. Dragonflies and water beetles arc also very useful. Anything which collects water should be dealt with. Old (ins, bottles, etc., should be removed aud buried; spouting must be cleared and receptacles emptied at least once a week and allowed to become- quite dry beforo refilling. Much may be done by the draining and abolition of swamps, tilling in of ponds, and depressions, and the straightening and cleaning of streams and ditches, or by the use of drainpipes. Unnecessary}, scrub may be cleared, but is useless if water remains. Where water cannot be removed, such should bo sprayed weekly with kerosene. The water must be co\erod with a complete layer of oil, two tablespoonfuis should cover fifteen tquare feet of Eurface. A good spray mixture v.. kerosene 69 parti:, fuel oil 40 parts. Ihe-f. oil films kill the. lar^a?

by preventing breathing. The addition of a little castor-oil to the kerosene gives a better film. Wind, is apt to destroy the lilm. The following larvieides are effective:—(l) Commercial cyllin 1 teaspoonful to the gallon of water or enough to make / the water milky when stirred. (2) Coaltar 1 pint; turpentine 1 pint, softsoap 1 oz., water to make up to two gallons. This will treat three hundred gallons of water. (3) Add copper sulphate to the water to be treated in the proportion of one part to five thousand of water. Stored water supplies may be screened (18 meshes to the inch, closed.in, or a layer of sawdust spread upon the surface. Against the egg stage "race suicide" measures may be used, Hang cigarette tins half-filled with water, or better still, hay infusion, under the

branches of trees. The eggs are laid in these. Empty the tins every' fortyeight hours into a caucepan and boil the water to destroy the eggs'." • The adult mosquito dislikes smoke—flat cakes of dried ccwdung, sprinkled with pyrcthrum powder, and then burnt may be tried. The burning <>f pyrcthrum powder alone, 131 b per 1000 •cubic feet in a closed room, is useful. This stupifito the insects, which must be swept up and burnt. Gitrohella oil will protect the face and hands to some extent. If this stains the 'clothes, the stain can be removed by oil of turpentine. Healthy sites for houses Bhould be chosen to windward of sWamps r etc., and as high as possible. Friar's balsam allays bites. Remember, however, the slogan: "No water, no mosquitoea."