218 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



Curiously enough, among the imported gipsy-moth enemies that 

 which most nearly resembles Blepharipa (if the practically identical 

 Crossocosmia be excepted) in the part which it will probably take in 

 the control of the gipsy moth is Calosoma sycophanta. No two of the 

 imported enemies differ more radically in their method of attack 

 than do these, the extent of their differences being fairly well exem- 

 plified by the fact that the gipsy moth eats Blepharipa, while the 

 Calosoma eats the gipsy moth, which is literally true. 



In one very important respect they are similar in that both are 

 able to exist continuously upon the gipsy moth without being forced 

 to have recourse to any other insect so long as the gipsy moth retains 

 a certain degree of abundance. Both work to their best advantage 

 and multiply most rapidly at the expense of the moth when the lat- 

 ter is superabundant. 



It is only necessary to consider the powers of reproduction (poten- 

 tially several thousandfold) possessed by the tachinid to see what an 

 enormous rate of increase is likely to prevail in localities where prac- 

 tically complete defoliation occurs without becoming so complete as 

 to bring about wholesale destruction of the gipsy moth through 

 disease. Under such circumstances a very large proportion of the 

 eggs deposited upon the foliage would perforce be eaten, as compared 

 with the proportion eaten were the caterpillars present in small num- 

 bers. The percentage of parasitism would remain practically the 

 same in both instances, but the gross number of parasites completing 

 their transformations would be tremendously increased with a result- 

 ing increase in the percentage of parasitism the following generation, 

 whenever the gipsy moth becomes unduly abundant. In like manner 

 the Calosoma, which works at a disadvantage when the caterpillars are 

 scarce, finds the conditions resulting through superabundance excep- 

 tionally favorable for its rapid increase. 



Theoretically, therefore, Blepharipa ought to act as an agent in 

 the reduction in the prevailing numbers of the gipsy moth whenever 

 it exceeds a certain degree of abundance, and this is the role which 

 it is expected to play. Theoretically, Calosoma will play practically 

 the same role. Together their activities ought to result in the break- 

 ing up of dangerous colonies of the gipsy moth, and thereby render 

 the work of the other parasites and of such native enemies as birds, 

 predatory bugs, etc., doubly effective. 



COMPSILURA CONCINNATA MEIG. 



Quite a good many of the parasites of the gipsy moth attack the 

 brown-tail moth also, but there is only one among them, Compsilura 

 concinnata (fig. 41), which is equally important as a parasite of both. 

 The remainder, if they attack both hosts, are more or less partial to 

 one or the other. 



