MOSQUITO PEST

Grey River Argus, 14 February 1929, Page 8

MOSQUITO PEST

EFFORTS TO COMBAT IT. RESULTS OF RESEARCH. Now is the time for householders to declare war on the mosquito (says the “N.Z. Herald”). The unusual amount of wet weather has been particularly favourable to them, for they breed plentifully in any stagnant water such as may be found in old tins and hoilow earthenware lying about in the garden, in drains and gully traps, and uneven roof spouting. Mosquitoes do not generally travel far, and whenever a householder is troubled by them it is a safe rule to look close at hand for the cause.

In most cases it will be found the householder has the remedy in his own hands by clearing away or applying kerosene to all water that breeds them and by cleaning up ,such weeds and long grass as affords shelter in the daytime to th e mature insect. The fact is that mosquitoes are worse than a mere nuisance. They are a potential source of real danger, and their elimination is a matter of importance to the whole community. The known facts about the mosquito in Auckland have been greatly added to as the result of the activities of a committee that took the matter in hand in 1925.

Some difficulty was at first experienced in obtaining the services of a suitable research officer, but this was overcome at the beginning of 1926 with the appointment of Mr D. H. Graham. who has since been carrying on investigations under the direction of Mr Archey, curator of the museum.

The first problem was to ascertain what species of mosquito are to be found here, and then to investigate their breeding places and general habits of life, especially in relation to biting human beings. So far seven dif ferent species have been identified, and their general habits have been, observed.

The common night-biting mosquito about Auckland is a small black one named culex pervibilans. The one that bites during the daytime has a white spotted form, and is known as aedes notoscriptus. These are the two that cause the greatest amount of trouble here. Culex pervigilans breeds and bites all the year through, although he is most in evidence in the warm summer and autumn period. They breed in anything that will hold water, including flower vases in a house if those are not frequently emptied, and they can also breed in a slow moving stream.

Wider problems than that of mere personal inconvenience were raised when Mr Graham discovered, be tween Dargaville and Waipoua, aedes notoscriptus and aedes antipodeus. both of which belong to the same genus as the dreaded yellow fever mosquito, aedes calopus. It is clear, therefore, that conditions in this province are favourable to the life of the yellow fever mosquito. Precaution has to be taken against their introduction by water carried in overseas steamers, and against their coming into contact with persons in New Zealand who have suffered from yellow fever, and so transmitting it to others. The effective control of these species may prove to be of the greatest importance to the health and prosperity of the community-

Hitherto the malarial mosquito, anopheles maculipennis, has not been definitely captured in New Zealand, al-, though Dr David Miller, chief of the biological department of the Cawthron Institute, once observed a specimen, which h e could not catch,that. had. the characteristic stance of the malarial mosquito. The importance of ascertaining whe'her the anopheles mosquito is in New Zealand has been increased by the occurrence of a supposed case of malaria near Christchurch, and the continuance of th o present indications is a matter of public concern.

One very important discovery of unique character made by Mr Graham is the existence in the Titirangi Hills of a species rejoicing in the name of rachionotomya argyropus. Its peculiarity, unique in the mosquito world, is that its larvae can breathe not only as other mosquitoes do, by means of a syphon protruding above the surface of the water, but also by means of a special gills. This enable it to remain below the surface of the water for an indefinite time, and thus although it is a vicious biter it is immune from control by the ordinary means of spreading a thin film of oil over the surface of the water where the larvae are. Mr Graham kept specimens at the museum alive in water for a month under a thick coating of heavy oil. This means that a new method of control must be found for this species. It is gratifying •o learn that through the activities of the civic authorities, in co-operation with Mr Graham, the mosquito pest about Auckland has been greatly reduced. The sanitary inspectors have done good work in draining out their breeding places and treating gully traps and other suspected spots with oil. For several years Devonport has been relatively free from them as a result of such preventative measures.

In permanent water areas mosquitoes are fairly adequately controlled by their natural areas, among which frogs, water beetles, lizards and native trout all receive honourable mention. Top minnows,- which can live in very small streams, have been found to be th e relentless enemies of the mosquito larvae, and they have been used with great success in the warfare in California. Mr Archey has a r.umber of them at the museum, and investigations are being made t 0 see how they may be most effectively «m--ployed here. Mosquitoes have four stages of development—the egg, larva, pupa, and the winged insect. The eggs are la,d upon water on which they float. At ter about 24 to 48 hours the ends open and the larvae escape. These are the familiar “wrigglers of pools and water barrels, and ar e found in almost any standing water. They remain in this state from one to three weeks, when the larva splits its skin and the

pupa escapes. This corresponds to the chrysalis stage of the butterfly. It then requires only a, few days of warm weather for the pupa to burst and for the adult insect to appear with wings ready to fly. and, in the ease of the female, with the ability to bite and lay more eggs. The application of the Mosquito Research Committee for funds with which to continue its work has been approved by the New, Zealand Institute, and is at present before the Hon H. Atmore, as Minister in charge of Scientific and Industrial Work. Dr Miller, of the Cawthron Institute, who is an advisory member of the committee, has strongly Recommended the continuance of the present research and the "widening of its scope.