IN TOUCH WITH NATURE

Otago Daily Times, Issue 21529, 29 December 1931, Page 4

IN TOUCH WITH NATURE

PESTILENT INSECT. By J. Drummond, F.L.S., F.Z.S. A mosquito swatted by Mr M. C. Astley, of Dargaville, North Auckland, on his desk one morning, has been sent for identification in case it should prove to belong to a species that carries yellow-fever. Last year, Mr Astley explains, an individual of the yellow-fever species was discovered in North Auckland and people were advised to take the offensive against the undesirable strangers. “It will be a relief to learn that my suspicions are groundless,’ Mr Astley writes. All fears were set at rest by Mr D. H. Graham, of the Marine Fisheries Investigation Station, Portobello, Dunedin, who, in 1929, published an important treatise on the mosquitoes of the Auckland district. He gives an assurance that the insect which alarmed Mr Astley is in no way like the malarial mosquito. It is a member of the common domestic New Zealand species, Culex pervigilans, present in the North Island and in the South Island wherever there are human habitations. Climatic conditions do not affect its capacity to reproduce. Its range is from sea coast to inland mountains. All the year round females lay their eggs in Auckland districts. In the month of June Mr Graham has taken hundreds of egg-rafts laid a short time before in water at _ a temperature of 42 degrees Fahrenheit. He has taken the grubs—he calls them larvas —from water that had ice on it, and in places where 15 degrees of frost were registered three days in succession. His extensive invstigations show that eggs of this species are in every sort of water —slowly flowing creeks, dirty or foul drains, street gutters, gnlly-traps, liquid manure barrels, drains around commercial premises, gutters on roofs, tarpaulin in railway yards, fire-buckets on railway platforms, drinking vessels in fowl-runs, flower-vases in cemeteries, puddles on roads, neglected water tables, lakes, lagoons, and wherever water accumulates for a few weeks. The egg-rafts afe, perhaps, the most interesting feature of a female’s activities, apart from its unpleasant taste for blood. As described by Mr Graham, The rafts are shaped like boats. Each raft, on an average, is loaded with about 265 eggs. The great lightness of the rafts, their shape, and the surface tension of the water, combine to keep them afloat in aiiy_ weather. When one was submerged experimentally, a film of air caught between the tapered ends of the individual eggs quickly brought it to the surface again. Each raft is merely a cluster of eggs. _ About 15 minutes are occupied in forming and loading it. The first egg is deposited on the surface of the water. Others follow at intervals of four seconds. When laying each egg, the female exudes a tough, elastic substances, which holds all the eggs together. For the mosquito’s purpose, the device is absolutely perfect. No improvement can be suggested. Mr Graham found an egg-raft adhering to the side of a jar from which the water had been receded. The raft was kept dry for 14 days. It then was placed in water, and the eggs hatched in 72 hours. While Mr Graham has dispelled fears as far as Mr Astley’s visitor is concerned, by fixing its identity, it should be explained that the yellow-fever mosquito is different from the malarial mosquito. Dr R. J. Tillyard states that Aedes abcentina, the carrier of yellow-fever, is plentiful m the warmer parts of Eastern Australia, but the organism that causes yel-low-fever is not present there. Still, the yellow-fever mosquito is mischievous in that part because it carries dengue fever and spreads it. The carriers of malaria are Anopheles mosquitoes and their allies. Men of science all the world over arc never tired of singing the praises of their fellow-workers who discovered that malaria is caused by a miscroscopical parasite, which passes through part of its life-history in human blood, and part in the body of a mosquito. It is stated that repeated experiments show without any doubt* whatever that a person can normally contract malaria by only a bite from an Anopheles mosquito or one of its < allies. The parasites enter the blood in this way. They penetrate the red corpuscles and destroy them. Multiplying by the formation of spores, the parasites attack fresh corpuscles, until the disease reaches its height. They may die off in time, and allow the patient to recover, or they may linger indefinitely, causing a chronic malarial condition. The stomach of a malarial mosquito was examined several days after the mosquito had bitten a malarial patient. The walls of the stomach were studded with round cysts; but these did not make the mosquito sufficiently ill to prevent her from attacking people and spreading the disease. Mr Astley watched his mosquito with its tail on the desk, its body at an angle to the desk, and its head reared. Female Anopheles mosquitoes, when at rest, seem to stand on their heads. Many people have asked Mr Graham what they should anoint themselves with in order to keep mosquitoes away. His reply is that the pestilent fellows can be kept away by only one means —namely, destruction of their breeding places. The necessity for eliminating stagnant water is shown by the remarkable fact that a small jam tin with a few ounces of water left undisturbed in it will cradle several hundred mosquitoes every few weeks. Tins, tyres, and untehsils, left lying about, should be flattened. Containers that cannot be destroyed, such as water troughs, should be emptied once every 10 days. Gold fishes or carp may keep ponds free by destroying mosquitoes in their early stages of life. Stagnant holes and gullytraps may be kept free by small quantities of oil, kerosene, or any crude oil that makes a complete film on the surface. This suffocates the larvae and the pupa;. In conclusion, for drinking water tanks Mr Graham recommends olive oil; only a small quantity on the surface will soon form a complete film and destroy the larva; without affecting the water’s drinking quality. Since Dr Casey A. Wood, an eminent American naturalist, visited New Zealand about eight years ago, he spent a great’ deal of time compiling a remarkable work. It is “An Introduction to the Literature of Vertebrate Zoology,” based chiefly on material in the Blacker Library of Zoology and other libraries of the M Gill University, Montreal, Canada. The title conveys no idea of the scope, size, value, interest and unique character of this large quarto tome with 650 pages, each page packed with information. At the end of six years’ effort, the work is sent out as merely a stop-gap until other hands publish a complete study of all vertebrate literature. This will be, perhaps. a series of 20 or 25 volumes ranking in importance with the imposing “ Catalogues ” of the British Museum, massed with details that make the mind reel in contemplation of men’s industry. Following Dr Casey Wood’s “ Introduction ” is an annotated catalogue of thousands of publications, occupying 470 pages. The work begins at the beginning, several thousand years before the Christian era, when primitive artists made frescoes of animals and cut pictures of them in rock. Aristotle, born 384 H. 0.. is the first serious writer on zoology whose works have survived. The treatise traces natural history from Aristotle’s times through the Middle Ages and later centuries, sketches naturalists’ voyages and expeditions, describes the rise of Darwinism, and explains evolution and modern methods of study. In the catalogue section, New Zealand is largely represented. The first reference is to Dr E. Dieffenhach’o “Travels in New Zealand,” published in London 88 years ago. The M'Gill University Libaries have 35 original sketches and coloured drawings by J. G. Keulemans for Sir Walter Buffer's “New Zealand Birds.” They disclose his method. He first sketched his subject from a specimen, and made notes to guide him in producing the finished picture. He was born at Rotterdam, and was easily the best and most popular painter of birds of his day, from 1870 to 1900. A copy of Dr Casey Wood’s work has been sent by the Oxford University Press, London, which published it with the compliments of the Blacker Library of Zoology, M'Gill University. Price, £3 3s.