SCIENCE AND INDUSTRY. 
could not have been foreseen if careful inquiries had been made before- 
hand in the countries from which they were brought. The case of the 
rabbit is often quoted, and many people in Australia appear to believe 
that the great destructiveness of this pest in Australia is quite peculiar 
to this continent. Any one familiar with conditions in England knows, 
however, that in country affording good cover for rabbits it is necessary 
to use wire netting to protect crops or young plantations just as is the 
case in Australia. The larger population, the severer winters, and the 
presence of natural enemies in the form of stoats and weasels are un- 
doubtedly the main or only reasons why rabbits are not such serious 
pests in England as in Australia. 
The natural enemies cf prickly pear, like those of other plants, fall 
into the two categories already mentioned. Owing to its succulence the 
prickly pear may in some cases form the principal food of certain 
omnivorous vegetarians in localities where it is abundant, yet there is 
no question that if the prickly pears were exterminated these forms 
would continue to thrive on the native vegetation or cultivated crops, 
hence their introduction would be quite unjustified. 
Amongst these omnivorous vegetarians certain rodents, snails, and 
insects may be mentioned. In the cactus regions of the United States 
and Mexico there occur several species of “ wood-rats” belonging to 
the genus Neotoma, which at times cause great havoc to prickly pear, 
utilizing it as food to such an extent sometimes as to exterminate it in 
some areas. However, since they are not restricted in their dietary to 
prickly pears their introduction to Australia would involve graye risks, 
and cannot be recommended. 
Mr. W. W. Froggatt has observed that the common snail (/elix 
aspersa) is specially fond of prickly pears in Sydney gardens, and 
therefore recommended that a very large snail (Achatina fulico), from 
Africa, should be introduced into prickly-pear areas.* This suggestion 
should be strongly opposed on similar grounds, since the snails are 
omnivorous vegetarians. 
Similarly, numerous vegetarian insects feed largely on prickly pear 
in America, but are known to feed also on other plants. Included 
amongst these are the fruit-fly (Ceratitis capitata), the mealy bugs 
(Pseudococcus obscurus, and Rhizococcus multispinosus), the Cuban 
cactus-scale (Palwococcus sp.), the plant-bug (Stylopidia picta), the 
blossom-injuring beetle (Trichochrous tevanus), the root-boring beetles 
(Cactophagus sp.), the cactus aphis (A. gossypii), and the cactus” 
red-spider (Tetranychus sp.). In Australia, also, certain native plant- 
feeding bugs have been observed sucking the juices of prickly pear, and 
at times causing damage to the plants thereby. These include the 
Rutherglen bug (Vysius venitor), and the coon bug (Oxycarenus lenti- 
culosus). The utilization of any of these cactus enemies for the destruc- 
tion of prickly pear is too dangerous an experiment to be attempted. 
Professor Harvey Johnston recently attended a meeting of the 
Executive Committee of the Institute, and sketched in general outline 
the conclusions arrived at by the Queensland Travelling Commission, 
and indicated generally the work which might be undertaken. He 
pointed out that there were a number of organisms which attack 
* Froggatt, W. W. Insects and Prickly Pear. Agricultural Gazette of New South Wales, vol. xxviii., 
p. 417, 1917. 3 
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