292 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



At the same time that the imported caterpillars were liberated, as 

 above described, a number of experiments in the similar colonization 

 of native caterpillars was begun, and in every instance in which they 

 were not overtaken with some well-defined calamity — fire in one 

 instance, starvation in others — they went through to maturity in 

 large numbers and in a perfectly normal manner. 



It is no longer to be doubted that in the case of tne imported cater- 

 pillars some element other than any which is operative during the 

 feeding period of the caterpillars in the spring is to be held responsible 

 for their wholesale demise. The uniform ill success which has invari- 

 bly attended the attempts to feed the brown-tail caterpillars from 

 imported nests through to maturity can no longer be considered as 

 either coincidental or the result of inexperience in this sort of work. 

 Something else is responsible, and in looking about for parallel 

 instances the results which have attended all attempts to feed cater- 

 pillars of the brown-tail moth, no matter from what source, out of 

 season, are possibly to be considered as comparable. 



Hundreds of experiments involving the feeding of native and 

 imported caterpillars upon lettuce during the late winter and early 

 spring have invariably resulted in carrying the caterpillars through 

 their first three spring stages and in their death before pupation. 

 This may be due to the character of the food. 



A smaller number of experiments in feeding caterpillars of the 

 brown-tail moth, which had been retarded in their emergence from 

 the winter nests, have always resulted in a manner not altogether 

 incomparable. Many thousands of these caterpillars have been kept 

 in cold storage for about one month after they would normally have 

 issued' and then placed upon their favored food plants in the open. 

 Upon several occasions when this has been done the caterpillars have 

 fed very freely at first, grown rapidly, and appeared to be perfectly 

 healthy. Then they would begin to die, almost exactly as the 

 imported caterpillars would begin to die in the fourth spring stage, 

 and it does not appear that any of them have ever completed their 

 transformations. This may be due to the weather conditions and 

 unsuitable food. It is believed that it is indirectly due in this 

 instance, and in the instances of the caterpillars from imported nests, 

 to the fact that both the one and the other have been subjected to 

 abnormal conditions during hibernation. The imported nests are 

 always exposed for a considerable period during the winter to an 

 unduly high temperature. The caterpillars are almost upon the 

 point of becoming active — sometimes they are beginniDg to become 

 active — when the nests are received at the laboratory. As soon as 

 possible after their receipt they are placed under out-of-door tem- 

 perature again, with the result that the caterpillars become inactive 

 and remain so until the time when they would normally have issued 



