396 
insect immigrant that it finds conditions 
for reproduction—a chance which may not 
occur once in very many times. Osten 
Sacken has pointed out that Hristalis tenax 
must have been brought here many times 
during four hundred years before it suc- 
ceeded in establishing itself. Undoubtedly 
many of these immigrants die upon our 
wharves when a lucky chance like crawling 
upon the clothes of a person and thus being 
carried out into the country might have re- 
sulted in the establishment of the species. 
Given the most favorable conditions and many 
species will be able not only to accommo- 
date themselves to a new environment, but 
certain of them will thrive better in the 
new than in the old. The effort to trans- 
port beneficial species from the Australian 
region and acclimatize them in the Nearctic 
region seemed a rash and unprofitable ex- 
periment on its face, and I confess that I 
for one had little hope of its success, yet it 
was successful with several species and 
transcendently successful with one. 
Much has been written of late about the 
success of the work in the introduction of 
beneficial insects by Mr. Albert Koebele 
into Hawaii, under the auspices of the 
Hawaiian government. Some of the in- 
troductions seem, without doubt, to have 
been strikingly successful. Mr. R. E. C. 
Perkins has reported at some length upon 
this success and, in commenting upon its 
reasons, Says: 
‘Tt becomes natural to ask why the suc- 
cess of the imported beneficial insects has 
been so pronounced here, while in other 
countries it has been attained in a compara- 
tively small measure. The reason, I think, 
is sufficiently obvious. The same causes 
which have led to the rapid spread and ex- 
cessive multiplication of injurious introduc- 
tions have operated equally on the bene- 
ficial ones that prey upon them. The 
remote position of the islands, and the 
consequently limited fauna, giving free 
SCIENCE. 
[N. 8. Vou. VI. No. 141. 
scope for increase to new arrivals, the 
general absence of creatures injurious to 
the introduced beneficial species, and the 
equability of the climate, allowing of almost 
continual breeding, may well afford results 
which could hardly be attained elsewhere 
on the globe. The keen struggle for ex- 
istence of continental lands is comparatively 
non-existent, and, so far as it exists, is 
rather brought about by the introduced 
fauna than by the native one.” 
Mr. Perkins’ reasons are all good, but he 
has not mentioned one prime reason of 
success, and that is that the most success- 
ful of the imported species have come from 
another portion of the same great faunal 
region, while others have been received 
from the region most closely allied, viz, 
the Oriental. 
Wallace took the view that the effectual 
migration of insects is, perhaps, more than 
with any other class of animals, limited 
by organic and physical conditions. ‘The 
vegetation,’’ he says, “‘ the soil, the tempera- 
ture, and the supply of moisture, must all 
be suited to their habits and economy ; 
while they require an immunity from ene- 
mies of various kinds, which immigrants 
to a new country seldom obtain.” 
There is much truth in this statement, 
but it must be remarked that, in practical 
experience, immunity from enemies of va- 
rious kinds is what insect immigrants find, 
not what they leave behindthem. It takes 
some time before they weave a new chain 
of organism preying upon organism. Our 
insect importations from abroad when they 
are of economic importance, and those 
from Europe are very likely to be of such 
importance, leave their old insect enemies 
behind them and frequently are not readily 
attacked by native ones. These last ac- 
commodate themselves to the new comer in 
time, but for a while he enjoys comparative 
immunity. The rapid multiplication and 
spread of Pieris rape, of Hematobia serrata 
