MOSQUITO CONTROL

Evening Post, Volume CXV, Issue 139, 15 June 1933, Page 9

MOSQUITO CONTROL

a YOKACIOUS FISH

POND AND RIViER QUESTION

EFFECT ON OTHER FISH

The malarial mosquito, Anopheles, has been found in New Zealand, and its presence has ' been attributed to accidental introduction in fruit or food imports. But such occasional discoveries are not evidence that it is, or, it likely to be, established, in New Zealand, any more than the occasional discovery on the coast of drifted watersnakes from Fiji is evidenco that; Net* Zealand is to be a.Snake', country.' Still, the, mere possibility that Anopheles may; become established should be, if possible, guarded against.

• Dr. David Miller reported as long ago as 1920 that "the conditions of the North Auckland Peninsula arc favourablo for the establishment/ of dis-ease-carrying mosquitoes, " and he saw at Kaitaia what /he thought was tho female of some Anophelinc "species ,of mosquito, but did not capture ono for identification. Later, Mr.. D. 11. Graham did identify Anopheles. Thcra is no evidence of actual carrying 'of malaria or other disease by an Anopheles mosquito in New Zealand. LIMITATIONS OF OIL. : Dr. Miller pointed out that the mosquito can be prevented from breeding by thel spraying of a, thin film of oil 0n...t0,tU0 water in which it, breeds. There are certain disadvantages (including cost) in using oil. . / In 1929-30 Mr., W. J- Phillipps, of the Dominion Museum, who had been working, on the mosquito menace from a new angle, contributed to the "New Zealand Journal of Science" a paper which he entitled "Use of Fishes for Control of Mosquitoes," in which lie introduced the subject of Gambusia holbrooki, a little fish whoso male is an. inch, and a half long, female 2£ inches. Gambusia cats tha larvae of mosquitoes. But the ques-' tion is whether Gambusia's destructive power would affect useful life as well as tho life that is not wanted. In his paper Mr. Phillipps wrote iii .1930: "Oil is costly if used continuously, as is necessary in' most New Zealand localities. The surface plankton is killed, and all other life in thewater suffers in gome degree. Tho water may become useless to stock, or even poisonous; while protected waterbirds are deprived of a habitat and a; food supply. Hence the suggestion that fishes may prove an effect ivo means ,of: mosquito-control in this country." INFLUENCE ON TROUT AND WHITEBAIT. Already there are indigenous fish iii Now Zealand that prey to som,e extent on the larvae of mosquitoes. The per- ■ formances of Gambusia in other coun« tries'indicate that he will vastly improve on their work. But will he do his job too. well? Will he- "■"clean up" the mosquito larvae and then attack tho eggs or young of trout or of indigenous freshwater fishes, such, as whitebait? Until these question's answered thefe is some fear that Gambusia, like the surface film of oil, may destroy to» much. The ichthyologists are therefor© moving with caution. Mr. Phillipps imported Gambusia in 1930, and the fish is today held under control, and under tests which, it is hoped, will # point to'the safety of other fishes from the mosquito-killer. Not till then cau. tho distribution of Gambusia tie attempted; He is now held in threw places —(1) a pond in Auckland Domain, in the tropical garden there; (2)' Lake Ngatu, a lake* near the Ninety, Mile Beach, containing no" fish, which, lake, Mr. Phillipps states, was suggested as most suitable by Mr. A. E. Hefford, Chief' Inspector of Fisheries;} arid (3) ponds at the N Biological Station, Masterton. No. lis the original breeding place of the fish imported in 1930. No 2is their first colony (ne-i cessary as too long a continuance-' iii No. 1 raised in-breeding dangers). No* 3 is the place where they will be specially tested in relation to trout qva aiid,' trout fly, whitebait, kokopu, etc. : SMALL BUT POLYGAMOUS. Perhaps it is an error to referytrf Gambusia as "he" because the male isj an inch shorter, and ten females arc born*, to each male, recalling a certaiili line in Kipling. But let that pass.' Never did imported fish enter New; Zealand at less financial cost to anyone! in this country. On application being made to the Pan-Pacific Science Institute at Honolulu (where Gambusia, imported' from the United States,, had won a great mosquito victory) members of the institute collected, the fish free of charge, the U,nion Company carried; them free, and the doctor on/the Niagara attended' £o. them free en route. Three consignments wore received m . 1930. In each ease about two-thirds died en route. Tho survivors numbered about half the number of tho Light Brigade before the charge at Balaclava, but their multiplying power is such that now there seems to be n» doubt that they will establish themselves in NeW Zealand1 if New Zealand, after the tests, is willing to have them. From ponds and lakes they can be transferred to rivers, if deemed not inimical to;other species.

SOUTHWARD TO FIGHT SANDFLY.

So many failures to induce Gambusia to live in temperate climates are on record that Mr. Phillipps was assured that it would not live in. New, Zealand; but three years after introduction it is doing well enough in thai liiorth. Bringing it to Masterton is one step southward, and Mr. Phillippa will shortly take a consignment to Duncdiii, to hold them in a pond there and. test-their vitality ►in cold Otago* If they pass the Duiiedin and tlio Masterton tests, they may find a new job' in Fiordland V ,and Otngo,.' controlling sandflies, but their effect on Bandflyj larva has still to be tried out. This is also an opportunity for the specialist to extend his knowledge of $ne sandfly. The life history of that pest should bo better known. In. his earlier efforts to handle Gambusia, which efforts entailed visits to| Auckland, Mr. Phillipps icceived financial help from the Department of Scientific and Industrial Research (Director,, Dr. E. Marsden), and latterly, with the permission of the Under-Secretary of tho Department of Internal Affairs, ho has'been able to co-operato with; tho Health Department, which has made a. grant for the purpose. Tho Wellington Acclimatisation Society has assisted by allowing tho. use of the Biological Station at Mastertpiv whero native freshwater life is being mItensivcly studied. I Mrs. E. Cannons, of Lower Hutt, who has been importing various pond and aquarium fishes for somo years, has recently made an interesting expcrimont for Mr. Phillipps. A largo single female Gambusia was retained from one of the. Masterton consignments and was kept by Mrs.-Cannons in water of a temperature of approximately 70deg day and night for six weeks. The result was that on the first day of June this female gave birth to thirty' young, which commenced; an. active life from the moment of birth. The mother ate several of lier own offspring, by mistake let us hope, and soveral died; but twenty-three ireinaia >yell and •active-