. 
SCIENCE AND INDUSTRY. 
fro, the dominance of any particular species of insect pest alternating 
with the dominance of its natural controls. The development of insects 
is largely dependent on food supply, though they are very sensitive to 
the influences of environmental stimuli, such as light, heat, moisture, 
chemical influence (odour), shade, wind, contact, &. Though their 
capacity for reproduction is very efficient, and their powers of assimila- 
tion are prodigious, they fluctuate very much in numbers. When eon- 
ditions are favorable, most insects will multiply rapidly. But they 
are as a house divided, one part preying upon and destroying the other, 
and the two often succeed each other like wave after wave of the ocean. 
Parasites finding innumerable insects to prey upon increase so rapidly ~ 
that they kill off their own means of support. They in turn succumb, 
and the host rallies once more while the numbers of its opponents are 
few. It is at such times as these, when both host and paras‘te are 
reduced, that numbers of parasites, which have been bred in special 
insectaries for the purpose, are liberated, in order to prevent the host 
insect from once more gaining that ascendancy which, sooner or later, 
makes it a pest. The recovery of the host precedes that of the 
parasite, as the latter has to depend on the host for its support. Hence 
Nasonia brevicornis. 
Adult female of Cryptolaemus 
montrouzieri Muls. (Essig. P. C. Jr. Ent.) 
its development aes behind that of its host, and many may die from 
starvation. One of the best examples of control by this method is the 
Citrus Mealy Bug (Pseudococcus citri) in California. It is one of the 
most difficult pests to control, but in several orchards in southern 
California it has been brought under complete subjection by the 
continued liberation of large numbers of entomophagous insects, prin- 
eipally Cryptolemus montrouziert, a ladybird less than half the size 
of its host. This, like many other parasites now being used in America, 
is of special interest to Australia, as it has been recently at work in 
many parts of Australia, ¢.g., at Manly (Sydney) on the Golden Mealy- — 
Bug (Pseudococcus aurilanatus), which was destroying the great pine 
trees encircling the beach. Oryptolemus montrouzieri has also been 
introduced into Hawaii with good results. a" 
While Australia has been a fertile source for many useful parasites 
for other countries, very little has been done here to exploit this method 
478 
« 
Dap 
