Jef 
and render an insect pest temporarily rare, but the moment thereis any 
~ relaxation the pest will undoubtedly return and within a year or two be as 
firmly fixed asever. With most insect pests, the range of food plants is 
so great and includes so many wild plants which can not be reached that 
it is only a matter of time before an apparently exterminated pest reap- 
pears. The world is too large and insects are too small and numerous 
to leave any chance of extermination by our puny efforts. Moreover, 
when. our best methods are scrutinized, it is seen that we have no insect- 
icide or form of control which is absolutely perfect and sure. Our gas 
treatment, which is our greatest triumph, in the hands of the most care- 
ful expert will not kill all of the scale insects on a badly infested plant, 
and in California, the home of this method, it is found necessary to 
fumigate every two or three years. 
Does anyone think for a moment and at all seriously that the San 
Jose scale is to be exterminated, and that its dissemination is to be 
prevented, whatever may be the legislation, and whatever quarantine 
steps may be adopted or exterminative measures put in operation? 
Undoubtedly this scale insect will overspread North America within 
the possible climatic range of the species, and ultimately, and at a not 
far distant date, will become established in Europe despite all possible 
preventive efforts. I question, in fact, if it does not even now occur in 
. many of the botanical gardens of Europe, in most of which are growing 
many plants from Japan, the probable native home of this scale, and 
whence it has four times been received by the Department of Agriculture 
the present year. 
The same interrogatories may be made in regard to any other insect 
similarly securely established in our midst. The history of every 
important injurious insect imported into this country, or spreading 
from some particular section within our borders, seems to have but one 
lesson. In each instance is noted a natural uninterrupted extension 
of the invaded territory, accompanied, as a rule, by an unusual and 
excessive abundance of the pest during its first years, and consequent 
serious losses in crops attacked, and, in subsequent years, a decrease 
in numbers and. amount of damage until a normal condition obtains 
and the pest is no longer especially feared. Note, for example, the east- 
ward march of the Colorado potato beetle and the purslane caterpillar, 
the southern spread of the imported cabbage butterfly, the extension 
westward of the horn fly, the migration northward of the harlequin 
cabbage bug and the house centipede, and similarly of fifty other insects 
which might be mentioned. 
It seems to me that the things here witnessed, namely, the natural 
spread and migration of insects, are inevitable and largely beyond con- 
trol in their larger aspects. I do not believe, to repeat, that it is pos- 
sible to limit for long the natural spread within our own borders of 
introduced insects any more than it is possible to prevent the coming 
of foreign insects to our shores. These are world movements, the work- 
7277—No. 20 2 
