JOURNAL OF ECONOMIC ENTOMOLOGY 
510 
[Vol. 16 
The writer is quite free to admit this has not yet been demonstrated 
except *in the case of the mealybug. 
The beneficial species which are to be employed must be comparative¬ 
ly free from the retarding effects of secondary parasites existing in the 
local fauna, which sometimes strongly attack the primary parasites used. 
Undoubtedly in some cases this factor will be sufficient to render the 
work unsuccessful, because'when by artificial manipulation a super¬ 
abundance of natural enemies of the pest is created, we thereby form 
an environment which is favorable for the secondary parasites. In 
other cases this will merely serve to reduce the degree of control. In 
most instances it will be practically impossible to foretell just what 
would happen in this direction and a practical attempt must be made 
in order to ascertain just what part the secondary parasites would play, 
and also the primary parasites of predacious insects. Undoubtedly this 
factor will limit or entirely prevent the control of some of our insect 
pests by this method. The attack of secondaries which occurred in the 
local fauna before the introduction of Aphycus leunsburyi has already 
greatly reduced the effectiveness of that valuable parasite, and this 
was also true in the case of certain parasites introduced into New 
England by the United States Department of Agriculture for control of 
the Gipsy moth. We can and do by careful work exclude new second¬ 
aries, but there are native secondaries which frequently attack the newly 
introduced beneficial insects. This of course cannot be prevented. 
It seems hardly necessary to state that these two principles, i. e., the 
adaptability of the beneficial insects to their hosts and their relation to 
secondary parasite^, are the ones on which in a large measure success 
will depend, and the degree of success attained will vary in accordance 
with the fulfillment of these requirements. The important thing to be 
impressed upon the general public, and the thing which has not been 
generally understood in the past, is that so far as our present knowledge 
goes not all pests are susceptible to control by the biological method, 
but that most of them can he influenced to some extent by the use of natural 
enemies, the degree of control being dependent largely upon ecological 
factors. When this is thoroughly understood there will be less false 
hope aroused and fewer disappointments and, in the opinion of the 
writer, the work will be strengthened thereby. 
In the actual work of locating new parasites in foreign countries and 
in collecting, shipping and rearing this foreign parasitic material, many 
very difficult problems are met. Transportation of material, especially 
when collected in such far-away places as India, China or South Africa, 
