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 

 prepupse and pupse, 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- 

 sitic 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 



