106 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
ures from this rule have not been encountered among the defoliating 
Lepidoptera as yet, and while exceptions will probably be found to 
exist, they will doubtless remain exceptions in proof of the rule. 
From this the rather obvious conclusion has been drawn, that to 
be effective in the case of an insect like the gipsy moth or the brown- 
tail moth, parasitic control must come about through a variety of 
parasites, working together harmoniously, rather than through one 
specific parasite, as is known to be the case with certain less spe- 
cialized insects, having a less well-defined seasonal history. To 
speak still more plainly, it is believed that the successful conclusion 
of the experiment in parasite introduction now under consideration 
depends upon whether or not we shall be able to import and establish 
in America each of the component parts of an effective " sequence" 
of parasites. This belief is further supported by the undoubted fact, 
that in every locality from which parasite material has been received 
abroad, both the gipsy moth and the brown-tail moth are subjected 
to attack by such a group or sequence of parasites, of which the 
component species differ more or less radically in habit and in their 
manner of attack. 
In the case of the gipsy moth and the brown-tail moth abroad, 
as well as in that of nearly every species of leaf-feeding Lepidoptera 
studied in America, there are included among the parasites species 
which attack the eggs, the caterpillars, large and small, and the 
prepupaB and pupae, respectively. Frequently, but not always, 
there are predatory enemies, which, through their ability to increase 
at the immediate expense of the insect upon which they prey, when- 
ever this insect becomes sufficiently abundant to invite such increase, 
are to be considered as ranking with the true facultative parasites 
when economically considered. 
It is, therefore, our aim to secure the firm establishment in America 
of a sequence of the egg, the caterpillar, and the pupal parasites of 
the gipsy moth and brown-tail moth as they are found to exist 
abroad, and until this is either done or proved to be impossible of 
accomplishment through causes over which we have no control, we 
can neither give up the fight nor expect to bring it to a successful 
conclusion. 
It was stated a page or two back that some species of insects 
support a parasitic fauna both numerous and varied, while others 
are subjected to attack by only a limited number of parasites, none 
of which can be considered as common. Notwithstanding the fact 
that somewhat similar differences are discernible between the para- 
sit ic fauna of the same insect at different times or under different 
environment, it is perfectly safe to elaborate the original statement 
still further and to say that some species are habitually subjected 
to a much heavier parasitism than others. Unquestionably the 
