PRICKLY PEAR

Ashburton Guardian, Volume 53, Issue 131, 15 March 1933, Page 8

PRICKLY PEAR

AUSTRALIAN MENACE. HOW IT WAS CHECKED. SYDNEY, February 16. Steadily, through good times and times of depression, and at an always increasing rate, a small insect has been earning foaj Australia the most staggering returns for any investment in the history of the Commonwealth's national endeavour. The fight to turn back the invasion of the prickly pear,'which was progressing at the rate of nearly two acres a minute, and rendered useless for productive purposes an area larger than Gi-eat Britain, has been waged silently and persistently by a small band of research workers. As a result of their work involving an expenditure infinitesimal in comparison with its yield, millions of acres are being won back for the grazing of cattle and sheep for mixed farming, for townships and other sources of national wealth. Introduced into Australia by Governor Philip in 1788, the prickly pear has been described as affording the greatest example known of the danger of invasion by a plant pest. The pear was obtained in Brazil and brought to Australia because of the cochineal insect, which lived on it, and from which dye was secured for the red coats of soldiers. , It stayed to become the greatest threat to the future of primary industries in Australia. By 1920 it had covered 60,000,000 acres and was spreading at the rate of 1,000,000 acres a year. Officers of the Commonwealth Prickly Pear Board, which works in close co-operation, with the Council of Scientific Research, commenced in 1920 a search in North and South America for the various insect enemies of the prickly pear, which exists in those regions. From headquarters at Uvalde, in Texas, the campaign was conducted and 140 different species were discovered which live on the pear. Then began the process of elimination. Careless or incomplete tests might have resulted in the release in Australia of an insect which might have also been a menace to plant life more disastrous even than the pear. It was found that one insect, while it refrained from attacking most plants other than the pear, was also an enemy of the rose. Others threatened garden and field crops, fruit and timber. One of the greatest difficulties which the board has to contend with was the acclimatisation of the insects which passed the tests and were imported to grapple with the pear. Brought from North America into Australia, they met with opposite seasonal conditions. The adult of the seed-destroying midge Asphondylia emerged in the early spring (March in the United States) and deposited its eggs in the young buds of the pear. In Australia the prickly pear flowered in September and October. The scientist took up the work of reducing the life cycle of the midge from the normal 12 months to six or seven, and by 1927 the midges were induced to emerge and lay eggs in the »buds of Australia's prickly pear. Nature had been taught a new trick. It was with the introduction of the cochineal insect and the cholinidea that the tide of battle commenced to turn. The prickly pear had achieved its maximum .spread by 1925, and then the ebb set in. Distribution of the cochineal, small, soft-bodied insects sheltered beneath a white secretion of fine silky threads was commenced on a wide scale in 1924, and achieved remarkable destruction of the pear pest. The advent of the Cactoblastis caterpillars imported in 1925 yielded in the second generation 2,450,000 eggs and the liberations commenced. The eggs laid in chains or "sticks," each containing up to 150, were easily distributed in small cartons, which were affixed under the pad of the pear. Not only do the Cactoblastis eat out the contents of the par, but they set up a bacteria which rots the stems and completes the work of destruction, bo rapidly do they multiply that the original 2750 have now grown to thousands of millions and fully 80 per cent of the pear in Queensland and 60 per cent, of the pear in north and north-western New South Wales has now been attacked. This does not mean that the whole of those areas has been reclaimed The pear grows again, but to a minor extent, and is again Each growth becomes weaker, until insufficient remains to support the Cactoblastis. By that time the farmer is able to do the rest and already 3,000 - 000 acres of country in Queensland, formerly infested by the pear, have been freed for pastoral and agricultural "Vhe cost of the distribution of the Cactoblastis is estimated at £IB,OOO a year Some of the land which has been liberated is worth £3 an acre for the prickly pear shows a marked preference for rich soil. But just work out the yield at 10s a acre on the millions of acres which have been liberated and tho millions which will come into bearing Those who are associated wit i the campaign emphasise that difficulties and dangers have still to be faced, and that complete victory is yet far distant; but prickly pear control so far is surely proving to be Australia a greatest investment. It is immeasurably the biggest piece of biological control work in history.