L28 (-VPSY AND BROWN-TAIL MOTHS. [Jan. 



ease. These reports were usually accompanied by specimens. 

 Often an entire web instead of being white would appear al- 

 most brown from its coating of tiny dead caterpillars. Webs 

 of this sort whose contents were carefully counted under the 

 hand lens showed that from 5 to 89 per cent, of the caterpillars 

 had been killed by the disease. At the same time it was not 

 felt that it would be safe to neglect winter work against the 

 webs because of this unexpected help from natural causes, - 

 a conclusion which was amply justified by the results of last 

 summer's work. During the caterpillar season of 1906 an 

 examination of infested white oak woodlands where the webs 

 were abundant and where no work had been done against the 

 moth demonstrated conclusively that the fungus had been an 

 important factor in checking the increase of the pest. But, on 

 the other hand, in places where the disease was present and 

 where from circumstances beyond our control no winter work 

 was done, as in certain sections of Boston and Lowell, a suffi- 

 cient number of brown-tail moth caterpillars emerged in the 

 spring of 1906 to cause severe annoyance and suffering, par- 

 ticularly in thickly settled residential districts. 



It was thought at first that the artificial propagation and 

 dissemination of the fungous disease throughout the infested 

 district might be a feasible and desirable undertaking; but 

 our examination in the spring showed that nature had already 

 done this work much better than man could possibly do, and 

 that diseased caterpillars were everywhere abundant in vary- 

 ing numbers. 



Could we feel assured that conditions would favor the occur- 

 rence of the disease annually over the entire district, the prob- 

 lem of combating the brown-tail moth would be much simplified. 

 rnfortunatelv, the history of all contagious diseases of in- 

 sects, whether bacterial or fungous, shows that their abundance 

 or -careity is almost wholly dependent upon climatic condi- 

 tion-, usually being favored . by warm, damp weather. This 

 h:is been repeatedly demonstrated with the infectious disease 

 of the Rocky Mountain locust in the west, the grasshopper 

 disease in South Africa and the well-known disease of the 

 chinch hiiir. which in certain years is of much benefit in western 

 corn and grain fields where the insect is over-abundant. In 



