MOSQUITO PLAGUE

Dominion, Volume 34, Issue 157, 29 March 1941, Page 13

MOSQUITO PLAGUE

Becoming Worse Every Season . CITY BREEDING PLACES Scope For An Expert, Says Health Officer Mosquitoes have been unusually abundant in Wellington this sum'mer. In parts of the city they have amounted to a ppsitive plague. The medical officer of health for the district, Dr. F. S. Maclean, said yesterday he believed they were becoming worse ever)'' year, and would continue do so unless steps were taken to deal with them. He believed there was sufficient work for an expert in mosquito control.

Early in the spring complaints were made of mosquitoes in the city area, and they became more numerous in the summer and autumn, when it was suggested that the insects were breeding in stagnant water in the basement of Victoria House, the ruined structure of which has stood untouched since it was gutted by fire about two years ago. The suggestion was supported by the frequency of complaints from offices in. the vicinity, and from guests staying at hotels in the heart of the city. Interviewed yesterday, Dr. Maclean said that complaints of the numbers of mosquitoes had come in to his department also; and on representations being made to the City Corporation, the basement of Victoria House was pumped out. He remarked, however, that unless it was drained entirely dry, and prevented from filling again, the nuisance would continue. The debris would prevent kerosene or oil from spreading to all breeding grounds there, and control would not be easy Many Breeding Grounds.

This, however, was by no means the only source of mosquito larvae, which .would breed in the smallest pool of stagnant water. Private ponds, unless stocked with goldfish, were prolific breeding places. Even the vases and receptacles used for floral decorations on graves in Wellington cemeteries had been found to be « source of mosquitoes,

Pools in the foundations of prospective buildings were a frequent playground of mosquito larvae. The excavations for the foundations of Broadcasting House, behind Parliament House, had filled with rainwater and become a breeding-ground till, by the co-operation of the Dominion Museum scientists, small tropical freshwater fish of the kind called Gambusla had been obtained from Auckland and placed in the water. They are flourishing, and keeping the mosquito larvae well under control. Dr. McLean said that it was the responsibility of the Wellington City Corporation to keep the city clear of mosquitoes; but his department was at all times prepared to co-operate in advising how to control the pest. The mosquito which was indigenous to New Zealand was not a transmitter of any harmful disease, though its bite was irritating. He said he thought there was scope for a man experienced in dealing with mosquitoes to be employed in controlling them. He believed they were becoming more numerous each year, and unless checked would eventually become as bad as in Auckland. Only the Female Bites. The New Zealand mosquito—or the commonest of the several native species • —is known scientifically as Culex Iracundus. It is a night-biting mosquito, with an irritating but not dangerous bite. To persons particularly susceptible or allergic to mosquitoes, its bite may cause painful 'swellings and even mild indisposition. Only the female mosquito sucks blood. The eggs are laid on the surface of water, and the larval and pupal stages are passed in the curious gymnastics typical of the infant mosquito -—ascending and descending head-over-heels in the stagnant water. The larva lives on minute animal life in the water; it ascends to the surface to breathe. Coating the surface of the pool with oil or kerosene is; therefore an effective method of killing the larvae.

In the second, or pupal, stage, the immature insect does not feed. When It finally emerges as a full-grown mosquito, it subsists ou plant juices. Throughout life, the male mosquito is content with a vegetarian existence. The female, however, must suck blood in order that her eggs may be fertile. Many sorts of mosquito can go several generations without blood, if it is hard, to come by.

In tropical lands mosquitoes transmit such dread diseases as filariasis. yellow fever, and malaria. There are some 2000 species. Work on the Panama Canal was long held up, and the French engineer de Lesseps frustrated, by the enmity of the mosquito. In many Pacific Islands mosquitoes are so numerous that more than 99 per cent, of the local natives are victims of mosquito-borne diseases. In the Ellice Islands, for instance, there are both day and night-biting species; the little black night mosquito is infuriating with its loud hum and smarting bite, so that natives and Europeans alike sleep under netting. At dusk and dawn there is a quarter-of-an-hour’s Respite, when no mosquitoes are afoot. By day flies the large, silent, painless Stegoinia mosquito, hovering in shadow because it cannot endure two minutes’ direct sunshine and live. Its bite is imperceptible, but it transmits filarial fever, from which all the islanders suffer, and elephantiasis, commonest disease of those islands. In their war with the mosquito the Islanders have three allies, the sun and the wind, which keeps these bush mosquitoes away from their dwellings, and the house-lizards, which live in the rafters and thrive on the mosquitoes which, gorged with blood, seek the shadows under the roof to digest their meal.