SAND-FLY PEST.

Press, Volume LXVI, Issue 20096, 27 November 1930, Page 9

SAND-FLY PEST.

ERADICATION METHOD. INTRODUCTION OF AUSTRALIAN DRAGON-FLY. If experiments now being conducted by the Department of Scientific and Industrial Research through Professor E. Percival (Professor of Biology at Canterbury College) are in two or three years' time proved successful, New Zealand may one day be permanently rid of the sand-fly pest. By the liberation of a certain species of Australian dragonfly at the Cawthron Institute and the Cass Mountain Biological Station, it is hoped ultimately to eradicate sandflies from the neighbouring areas and so to justify a wider application of this unique treatment. Professor Percival explained to a reporter of The Pbess yesterday that a species of dragon-fly was found iu Australia in a stream in which, although all conditions were favourable no sand-fly larvae were to be found. Conversely, when the species was absent, the sandfly larvae were common. It was established in the laboratory that this dragonfly ate the larvae of the sand-fly, the conclusion being that the scarcity or absence of sand-flies in any stream was due to the presence of these dragonflies. Introduction in New Zealand.

It was suggested that the species might usefully be introduced into New Zealand, and two consignments were received. Of the first, there was only a single survivor; but of the second, about 25 dragon-flies were still alive, and these were divided between the Cawthron Institute and the Cass Mountain Biological Station, from both of which they were liberated in neighbouring streams. "Nothing of the result of the experiment can be known until we find out whether the insects can be recovered and whether they are increasing," said Professor Percival. "They can't produce any effect for a very long time until they become sufficiently numerous to reduce materially the number of sand-fly larvae. They were simply put into the streams and left to fend for themselves. My hope is that one batch of eggs will be laid this year. If that happens, the species will be fixed and will spread, possibly, in about a century, covering the whole of the South Island." Sand-Fly Larvae Under Water. It was not generally recognised, he added, that the larvae of the sand-fly were usually found in running water. The pupae usually fastened on to stones in the bed of the stream, and the insects came to the surface in bubbles of gas. They might thus be carried half a mile downstream before they reached the surface and were liberated into the air. One fact that militated against the success of the treatment was that the sand-fly could do with different aqtiatie conditions from the dragon-fly.