Biological Control Not Simple

Press, Volume CV, Issue 31030, 9 April 1966, Page 9

Biological Control Not Simple

“I am sorry that I cannot report any prospects which can be classified as better than ‘long shots,’ but I hope I have convinced E.M.R. and others that we are investigating all promising avenues in the biological control of the grass grub,” says Mr B. B. Given, who is in charge of biological control at the Entomology Division of the Department of Scientific and Industrial Research at Nelson, in a statement replying to a letter from a correspondent signing himself E.M.R.

E.M.R. said he was very interested to read what Mr Given had to say recently about grass grub control in “The Press,” but he was appalled to think that a “long shot” was the best the Government had been able to do so far to get away from the use of costly and dangerous insecticides for the control of grass grub. (Mr Given’s remarks had been on the introduction of Patagonian wasps as a possible parasite of grass grubs). “I would point out that in biological control activities we cannot manufacture or produce at will beneficial species to control pests,” says Mr Given. “We must therefore at times use ‘long shots’ as our best means of attack.

“Generally in pest control we are attempting to control an introduced species which has got out of hand in its home of adoption, having left its normal natural enemies behind. In the case of control of the grass grub we have a pest species which is not only a native but also is confined to New Zealand. We have altered the rural environment so radically with our extensive pastoral and cropping areas that the grass-grub has been able to move into an entirely new environment which provides almost limitless food and scope for reproduction. Unfortunately the natural enemies of the grass-grub have not adopted this new pastoral environment to the same extent and so while beneficial factors for the pest have increased, its natural limiting factors have largely disappeared. The result is a perfect set-up for grass-grub epidemics. “Being unable to use longadapted controlling factors without materially disrupting our pastoral practices, /we are forced to do the next best thing and try controlling factors from related (but not identical) species from overseas. This approach involves a series of ‘long shots.' First attempts in this direction

were made in 1921, later in 1928 and in 1945 to 1952 I spent my time in Australia studying the prospects there and finally sending some 14,000 pairs of wasps (of 13 species) to New Zealand for trial. Currently we are trying wasps from South America, and will utilise any parasite or predator which appears promising, at the same time sending live grubs to France and England for testing with disease organisms and Northern Hemisphere parasites. Patagonian Wasps “It will be noted that we have made our initial liberations of Patagonian wasps in areas as free of insecticide contamination as possible and it can be stated several weeks after liberation, wasps were still active in the areas, indicating reasonable freedom from D.D.T.,” said Mr Given. E.M.R. had written: “I trust that the Patagonian wasps have been bred strongly D.D.T. resistant or they will not last long. Their first bite of our New Zealand grass grubs will be fatal. “Do you know that a paddock where trials to test insecticides were being laid down was found to have 10.61 b of D.D.T. an acre in the top six inches from farmer application? (New Zealand Journal of Agricultural Science, volume 8 No. 1, page 174.)

“Not surprisingly, none of the D.D.T. treatments had any noticeable effect on the grass grub population. Probably hundreds of thousands of acres have as high or higher amounts, but farmers are still pouring on more regardless or ignorant of the fact that it is a colossal waste of money. “D.D.T. in serpentine super raised the price 80 per cent and the prills that we have to use now are very expensive.

“The Government must give the scientists enough money to find alternatives to insecticides.”