CONTROL OF PRICKLY PEAR 415 



such insects were tested relative to the possibilities of their 

 attacking economic plants, and freedom from parasites being 

 ensured. The material received from America was transferred to 

 quarantine buildings at Sherwood, near Brisbane, where they 

 were bred through one or more generations as an additional 

 safeguard against the accidental introduction of their parasites. 

 At Sherwood, also, further tests were conducted with respect to 

 the possibility of the introduced insects attacking crops and other 

 useful plants. From Sherwood the insects were eventually 

 forwarded to acclimatising and breeding centres where, as a rule, 

 the first liberations were also carried out. The acclimatisation of 

 North American insects in a country where they are faced with 

 opposite seasonal conditions naturally presents considerable 

 difficulties. Generally it has been found that repeated shipments 

 of a species of over a period of one or more years have been 

 necessary before it has become established, but in a few cases 

 efforts have failed altogether. 



A number of species have become acclimatised to Australian 

 conditions, and among them the moth Cactohlastis cactorum, whose 

 larvae tunnel through the tissues, is the most important. The 

 cochineal, Dactylopius tomentosus, became distributed almost 

 throughout the infested areas, and the plant bug, Chelinidea 

 tubulata, spread in countless millions in many localities. The red 

 spider, Tetranychus opuntice, also covered many thousands of 

 square miles. A. P. Dodd, in his 1929 Report on this problem, 

 stated that the established complex of insect enemies was already 

 bringing about a considerable degree of control of this noxious 

 pest. In the heart of the prickly pear country it was possible to 

 travel for 100 miles without seeing any healthy plants. In his 

 1936 paper Dodd emphasises that the Board's policy was based 

 upon the conception that biological control offered best chance of 

 success if a carefully selected group Xtf species working more or less 

 in association was established. It was unforeseen that the 

 outstanding success, evident in 1936, would have been effected 

 by the agency of a single species of insect in the space of a few 

 years. Nevertheless, this is what actually has happened, and the 

 insect in question is the Phycitid moth, Cactohlastis cactorum. The 



