PRICKLY PEAR PEST.

New Zealand Herald, Volume LXIII, Issue 19452, 7 October 1926, Page 11

PRICKLY PEAR PEST.

FIGHT BY SCIENTISTS.

SAVING FARM LANDS. GOOD WORK OF PARASITES[from our own correspondent. ] SYDNEY. Sept. SO. One of the greatest battles in the cause of Australian primary production is being fought by the scientists who comprise the Commonwealth Prickly Pear Board. How great a curse the prickly pear is may be judged from the statement that 68,000,000 acres of good grazing or farming lands in New South Wales and Queensland are in the grip of the pest, which is spreading at. tho rate of 1,000,000 acres yearly, or as the mathematician puts it before ns, at the rate of 114 acres every day of the year. With little publicity, but with an enthusiasm which must eventually spell success, a handful of young Australian scientists are battling with this menacing problem. Their task is stupendous, but they declare they have reached a stage where they can say with confidence that the pest will be checked. America was the primary homo of most of the prickly pears which now infest this country, and it provides tho main source of supply of their natural enemies, parasitical insects. A collecting station has been established by tho board in America, and this maintains a steady stream of moths, larvae, beetles, insect eggs and fungi. The nerve centre of the organisation is housed in a small wooden building at Sherwood, near Brisbane, and there all experimental work in the preliminary stages is carried out. Field stations continue tho experiments, and there insects which have passed exhaustive tests at Sherwood are liberated, and their subsequent history is studied. Insects in Quarantine. On arrival from America tho insects are quarantined in case they themselves might be carrying parasites which it would be fatal to liberate. Only eggs or newlyhatched larvae are / removed from the quarantine station and placed in the experimental cages. Tests of their effect on valuable plants and trees are made by confining them to these, and if they starve to death they are placed on the "white list" as being friends, and not foes, of the agriculturist Through some cause which is as yet a mystery closely-related varieties of the same insect show remarkable divergencies in tastes and dislikes. It is necessary to ascertain in the case of each insect on which prickly pear it can live, and if it can thrive on all of them, and whether it shows preference for any particular species. Cochineal insects have been doing their good work of ravaging, the pear for several years, and have cleared thousands of acres. Recent experiements have discovered even more powerful enemies of the pear. Chief among these is a red and blackbanded larvae from Argentina, known to .science as Cactoblastis. Tho number of larvae of this species now under observation totals about 3,500,000, the product of 2800 brought to Sherwood last year. By boring into the pear, Cactoblastis feeds on the substance of the plant, leaving , nothing but a rotting outer husk. They destroy one plant before passing to another. With their remarkable powers of reproduction, allied to the rapidity of their destructive work, the scientists are expecting Cactoblastis to rid thousands of acres of pear in a few years. Another Active Enemy. Another enemy of the pear is a fly, Asphondylta Opuntiae, which does its work by laying its eggs at the roots of the minute leaflets surrounding the fruit bud. As the fruit develops the lai-vae hatch out inside. Throughout the summer and autumn they lie dormant, but during winter comparative rapid development takes place, and with the advent of spring the fly emerges to repeat the cycle of the previous generation. The presence of the larvae causes the fruit to | rot and drop off, and as the spread of the pear is dependent on the distribution of its fruit, the pest is kept in check to a considerable degree.

The sole usefulness of the fly to the scientist is >in the coincidence of its life cycle with the fruiting period. The most interesting natural history experiment ever conducted in Australia is the scientists' efforts to change the emergence of the fly from March or April, as they do in North America, to October. The next two weeks are expected to see this remarkable experiment carried to a successful conclusion.