DETERIORATED TROUT

Dominion, Volume 13, Issue 59, 3 December 1919, Page 3

DETERIORATED TROUT

DEFICIENT INSECT FOOD THE UTILITARIAN DRAGON FLY DR. R. i. TILLYARD INTERVIEWED. Visiting Wellington at the present time is Dr. B. J. Tillyiml, M.A. B.Sc., F.Z.S., F.E.S., Linnaean Macleay Fellow in Zootygy, of the Sydney University, who, mider an arrangement with the Now Zealand Government, is visiting New Zealand to study onr insects in their relation to trout feed. It is well known that the trout of Lake Botorna have deteriorated considerably during the past fewyears, and as deterioration in animals, birds, or fish as a rule is related to their food, supplies, it was only natural to infer that the trout feed at Rotorna nnd Taupo was becoming deficient, the only alternative theory to that being that the trout, which reached abnormal size and weight 20 years ago, were 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, put in three weeks inßotorua, and subsequently yisited Lakes Tarawera, Taupo, and also stayed ft while at Tokoanu. TIo is now on his way south, where ho will make Lake Wakatipu his headquarters for a time, afterwards returning to go over the same ermmd—or rather, water—in the North Island. This procedure would 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 revisits Botorua nnd its vicinity in February. Dr. Tillyard said he was unable to give any definite information ns to his work so far; besides, his report would first of all have to bo forwarded to the Government. All he could say in a general way was that there was sufficient evidence to show that the Government would 1m wise to adopt scientific methods in connection with the trout, if it did not wish them to further deteriorate.. Ho further stated that euch deterioration would not hnve taken nlace had overstocking been nrevented—overstocking in relation to the food sumilv. In Nature there was alwavs to be found a pretty fine balance between the lifo in a district and tho food 6upply in that district, a balanco that was very easily upset by human interference. Tho 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 fetf largely on flies of nil sorts, and were particularly fond of diacon flies, which might with advantaee be introduced into New Zealand in greater variety than was at present tho case. Draaon Fly v, Mosquito Dr. Tilivai'd offered tho • information that whilst there were only some ten varieties of dragon lly in New Zealand, there were two, hundred m Australia, ana they were a highly beneficial insect to mar., inasmuch as. they lived oil noxious insects, and wero exceedingly partial to irosciuitos. Indeed, Dr. Tillyard went as far .as to say that the introduction into New Zealand of certain varieties of tho drawn fly would servj largely to keeD down the mosquito as a pest. The utility of the dragon tiy in that oirection was ascertained recently through the desire of tho Coinmonw.'alth Government to nut some "malarial" men (soldiers from New Guinea) on to blocks of land in Victoria. . Several Mocks were offered, but had to be rejected as they harboured tho mosmiito, which would only do harm by spreading malaria in Australia. At. last a block was found free of the nest, nnd it was found that that condition had been brought about by the presence of an unusual number of wagon flies, which had wiped out tho mosquitoes, if ever they' ban' existed in that locality. That was at Swan Hill, in Victoria. Tho dragon fly was an absolutely harmless fly to all save noxious insects, so it could be regarded as most 'beneficial to mankind. Dr. Tillyard said that tho mosquitoes which existed in New Zealand were not the variety that carried tho virus of yellow fever, but they seemed extraordinarily fecund in tho north. Ho had seen 'literally millions of larvae of mosquitoes at Kotorua within an area the sizo'of sin ordinary room. So far New Zealand had not tho worst varieties, but the' fact that thnt was so now gave no guarantee for the future. >( "I don't think your Government VO'S the scientists enough to do this kind of research work," said Dr. Tillyard. "What a trifle it would mean to your G< eminent to spend .£IO,OOO, if it meant keeping out yellow fever or malaria.,, We have malaria in Queensland, anfj:.. they nave it up in the Islands. Why- sioiild tfew Zealand bo exempt?" The swamps round Uotorua and the north of Auckland were fine brooding grounds for mosquitoes. and the utmost endeavour should be made to keep them down by introducing their natural enemy. Most of the Australian dragon flies haunted running waters. ThJy had only two varieties that went into the swamps after their food, but one never knew what habits an insect would develop in a new country. Which wi'.s the most ellicntioiw for the purpose in view in this country would have to be ascr-rt.'iined by exp"rim«ntiii.«: mht through the Dominion. The drawn flv, - as beautiful as many butterflies to the eye. would not go for the sandflies, but there were two varieties of mayfly which had Wn known to clean up co'onies of sandflies. Tt will interest many to learn .that Dr. Tillyard is to lecture before Hie . Wellington Philosophical Society this evening on "Neuropteroid Insects."