452 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
habitats, and degree of injury of all species. The cactus insect bulletin 1 
proved an invaluable guide along such lines. All of the principal cactus 
insects were found in the field, and two new species were discovered. 
The work of rearing the field-collected insects free from natural 
enemies occasioned the devising of methods applicable to each species, 
and drew heavily upon the knowledge of their life-histories obtained 
by the observations cited above. 
The cactus insects occurring naturally in the field in North America, 
are, in general, rather heavily handicapped by natural enemies. The 
procedure followed was to confine the collections of selected species 
with their host plant in the cloth cages above described. Each species 
was, of course, collected most readily in certain stages, and by certain 
methods, the details of which need not be mentioned. Upon appearance 
of adults, these mature individuals were transferred to another cage 
containing only clean cactus, and placed under suitable conditions to in¬ 
duce mating and oviposition. The deposition of eggs in perfectly tight 
cages insured a stock free from enemies. Eggs so laid were collected and 
placed in other cages where only clean cactus was available. These eggs 
were the beginning of a parasite-free stock which was shipped either as 
eggs or in a more favorable stage of development, depending upon the 
species in question. 
It is apparent that the capacity-allotment of field-collected adults to 
a single cage should normally produce sufficient eggs with which to stock 
to similar capacity a number of such cages. Experience in rearing 
taught the number of individuals of a given species which constituted 
the capacity of the cage. There was derived, then, a rough ratio of ex¬ 
pansion in terms of cages from generation to generation for each species. 
These principles, arrived at by field and laboratory experience, when 
applied to operations in Australia where the immediate need was ex¬ 
pansion, greatly expedited the increasing of the introduced insects. 
Since the cottony cochineal insects produce living young instead of 
laying eggs, and because of the nature of their natural enemies a differ¬ 
ent procedure was necesasry. Young cochineal crawlers where abundant 
have a tendency to mass themselves on the topmost spines of the plant 
on which their parents live. By holding a piece of cheese-cloth beneath 
such a crowded spine and thumping the spine, the crawlers may be 
transferred to the cloth without injury. This cloth is then placed in a 
cage containing cactus which has undergone a most minute examination 
x The Principal Cactus Insects of the United States, by Hunter, Pratt and Mitchell 
(U. S. D. A. Bur. Ent. Bull. 113, 1912). 
