TROUT FEED QUESTION.

New Zealand Herald, Volume LVI, Issue 17335, 5 December 1919, Page 5

TROUT FEED QUESTION.

RELATION TO DETERIORATION DOMINION'S INSECT LIFE. INVESTIGATION BY SCIENTIST [BY TELEGRAPH— CORRESPOXDEVT.] WELLINGTON. Tfcnradas. Visiting Wellington at present is Dr. J,'. J. Tillyard, of Sydney, who, undfr arrangement with the New Zealand Gu\en,. ment, is touring the Dominion to siq'dy insects in their relation to trout feed. The trout of Lake Rotorua have detorionUr-d considerably during the past tew year?, and as deterioration in animals, bird?, or fish as a rale is related to their food supplies Dr. Tillyard says it is only natural to infer that the trout feed at Rotorua ami Taupo is becoming deficient. The'only ' alternative theory to that is that the trout which reached abnormal size and weight 20 years ago are gradually coming down

to normal by a natural process. Dr. Tillyard's specialty is the study of insect life and to observe what part they play as trout feed. He, with Mr. Miller. Government entomologist, and Mr. H. Hamilton, of the Dominion Museum staff, spent three weeks in Rotorua, and subsequentlv visited Lakes Tarawera, Taupo, and also "stayed; at Tokaanu. He is now on his way' south, where he will make Lake Wakatipu his headquarters, afterwards returning to go over the same ground in the North Island. This procedure will be necessary, as the insects were, in most cases, in' a. larval stage when he was there last month, and they will be "on the wing" when he re- ; visits Rotorua and its vicinity in February. Dr. Tillyard said he was unable to giv« any definite information as to his work so far.- His report would first of all have to be forwarded to the Government. All he could say in a genera! way was that there was sufficient evidence to show that the Government would be wise to adopt scientific methods in connection with the trout if it did not wish them to further deteriorate. He further stated that such deterioration would not have taken place had overstocking been prevented. Upsetting the Balance. There was always to be found a fine balance between the life in a district-and the food supply in that district, a balance that was very easily upset by human interference. The introduction of trout was safe up to a point, but they had been allowed to increase in such numbers that there was not enough food to go round.. - Trout fed largely on flies of all sorts, and were particularly fond of dragon flics, which might with advantage be introduced into New Zealand in a greater variety than was at present the case— » '-. The visitor offered the informatioriTthat while there were only some 10 varieties of dragon fly in New "Zealand, there were' 200 in Australia, and they were a highly beneficial insect to man, inasmuch as they lived on noxious insects, and were exceedingly partial to mosquitos. Indeed. Dr. Tillyard went as far as to say that the introduction into New Zealand of certain varieties of the dragon fly would serve largely to keep down the mosquito. ; The utility of the dragon fiy in that riirec-' tion was ascertained recently through; the' desire of the Commonwealth Government J to put some "malarial" —soldiers from , J New Guinea—on to blocks of land; m Victoria; Several blocks were offered.

bat had to be rejected, as they harboured the mosquito, which would only do harm by spreading malaria in Australia. At last a block was found free of the pest, and it was found that the condition had been brought about by the presence ot an unusual number of dragon flies, which I had wiped' out the mosquitoes. .That was at Swan Hill, in • Victoria. "The , dragon fly was an absolutely harritfess I fly to all save noxious insects," so it could be regarded as most beneficial to niankind. • ' Keeping Out Disease. n Continuing, Dr. Tilly&rd said the mosquitoes which existed in New Zealand, yievc not the variety that carried the virus of yellow fever, but they seemed extraordinarily fecund. In the North he had. seen literally millions of larvae of mosquitoes at Rotorua. within an area the size of an ordinary room. So far New Zealand had not the: worst varieties, but the fact thai, that was so now gave no guarantee for the future. "I do not think your Government pays the scientists enough to do, this kind of research work," said Dr. Tillyard. " What a trifle it would mean to your Govern? ment to spend £10,000 if it meant keeping out yellow fever or malaria. We have, malaria in Queensland, and they have i£ up in the Islands. Why should New Zealand be exempt?!' The - swamps- round Rotorua and the north of Auckland, .he added, were fine breeding-grounds for mosquitoes, and thu utmost endeavour should be made to keep them down by introducing their natural enemy. Most of,the Australian dragon-, flies haunted running waters. They had» only two varieties that went into, ihe. swamp after their food, but one never' knew what habits an insect would develop, in a new country. N