February, ’24] 
HAMLIN: PRICKLY PEAR PROBLEM 
61 
totals 30,000,000 acres. In Queensland over 24,000,000 acres are 
infested and in New South Wales upward of 5,000,000 acres. These 
almost incomprehensible figures total 46,000 square miles—or an excess 
of 5,000 square miles over the entire area of the State of Ohio! 
During 1916-17 the excess of cactus over all Australian crops was 
about 4,000,000 acres. 
The pear infestation extends roughly from Sydney, New South 
Wales, to north of Rockhampton, Queensland, or from 22 degrees to 30 
degrees South Latitude. In general the rainfall of eastern Australia 
decreases toward the interior, and prickly pear is found mainly in the 
region of from 20 to 40 inches of annual rainfall. The pest grows in 
open forest country as well as on open stretches. 
During the past ten years in Queensland alone the average annual 
spread has been more than 800,000 acres, or 2,300 acres per day. The 
annual increase in both States is today well over one million acres. The 
pest propagates readily both vegetativelv and by seeds, so that flood 
waters, cattle and birds are the more important agents of dissemination. 
The birds implicated are the emu, crow, and the black magpie. 
Species of Opuntia in Australia 
About fifteen species of Opuntia are naturalized in Australia. Two 
species, the “common pest pear” (Opuntia inermis ) and the “spiny pest 
pear” (0. stricta), cover the bulk of the cactus area. 
Early Attempts at Control 
Since 1900 the importance of the pest has become increasingly ap¬ 
preciated, and many suggestions for its riddance have been considered. 
These proposals have included its destructive utilization as cattle feed, 
green manure, and for manufacuring alcohol, potash, oxalic acid and 
fibre for paper making. All proved futile. 
Numerous mechanical devices for pear destruction are useful on small 
areas of very valuable soil. 
Chemical research has determined that the injection of certain arsenic- 
als is the best method of poisoning prickly pear. The applicability of 
this method is limited to areas of scattered, accessible pear and the cost 
limits its usage to valuable land. 
While most important, these measures do not alter the face of the 
national problem. 
Preliminary Biological Work 
In 1910 Mr. Henry Tryon, Government Entomologist of Queensland, 
