Sandfly Control In S.I.

Press, Volume CVII, Issue 31522, 9 November 1967, Page 11

Sandfly Control In S.I.

Although a great deal , of information on the I control of sandflies exists, mainly as a result of work in other countries, there are special circumstances in the breeding habits of the New Zealand species, or legal restrictions on the use of insecticides, which restrict their application. Mr L. J. Dumbleton, of the entomology division of the Department of Scientific and Industrial Research, said this' in reply to a letter to the I editor of “The Press” from a correspondent, “A Sufferer,” who wrote: “Since New Zealand is; keen to develop its tourist' industry, surely some re-| search should be earned out into methods for controlling: the sandfly. At present there seems to be no effective way of eliminating this pest, and the various insect repellents on the market serve only as| a temporary relief. It would add much to the comfort of many overseas visitors if a remedy could be found.” Mr Dumbleton said that ultimately insecticides might be found which were effective against sandfly larvae in streams and at dosages which were accepted as doing no permanent harm to fish or fish food and which left no persistent residues to affect adversely other wildlife but this would not solve the problem of sandfly control in the South Island. “Reduction of the number of adult sandflies in a limited area may be attempted directly by the use of sprays or thermallgenerated insecticidal fogs or smokes containing an insecticide such as D.D.T. “This may give protection to the restricted area treated for a short time, but there is usually rapid reinvasion of the treated

area by sandflies which have bred outside the area.

This method may be useful for protection of picnic grounds, etc., for a day, but the cost of repeated treatments at short intervals is likely to be warranted only in the case of scenic spots, residential areas, or work areas which are in constant use by relatively large numbers of people,” said Mr Dumbleton.

"The most effective method of control is by the use of insecticides like D.D.T. in the streams in which the sandflies breed, at dosages which do not cause mortality of fish. Such dosages do, however, cause reductions, often transitory, in the numbers of other insects, etc., which form the food of fish. “More serious, however, is the fact that the residues of D.D.T.—a very stable and persistent material—tend to be concentrated as they move up the insects-fish-birds food chain with consequent illhealth and mortality in predacious fish and birds.

"Where the sandfly is a vector of disease of man the ncessity for its control overrides considerations of damage to wild life and D.D.T. and similar compounds are the insecticides of choice,” said Mr Dumbleton. Mr Dumbleton said when the necessity for control was less urgent, as in the case of pests in recreational areas, etc., it was desirable that the insecticide used be unstable or non-persistant so as to avoid problems due to the persistence and accumulation of residues which would have adverse effects on wild >life. Such insecticides, at present some of the organo-phos-pborus group, were both more I costly and less effective than 'materials like D.D.T. “Two species of sandfly are avid biters in New Zealand. ' One is characteristic of forest-

ed areas, particularly on the West Coast of the South Island. It breeds in small streams under forest cover from sea level to 3000 feet often in mountainous terrain, and the adults tend to concentrate on river margins, lake shores, and beaches which may be long distances from the actual breeding places. “The treatment of all such breeding places over a sufficiently wide radius from the place to be protected is judged to be not feasible,” he said. “The second species which is the pest sandfly throughout the North Island and the northern coasts of the South Island is more amenable to control since it breeds in streams which being mostly in open country of easy topography are readily accessible for insecticidal treatment, and the flight range of the adult is probably not great. “Irrespective of whether they are physically feasible or not such insecticidal treatments of streams cannot be employed in New Zealand since they are at present prohibited by the Fisheries Act or regulations under it or other anti-stream-pollution acts,” said Mr Dumbleton.