1908.] PUBLIC DOCUMENT No. 73. 167 



this work cannot be done until the opening of the caterpillar 

 season in 1908, the preliminary arrangements for a study of 

 the disease have been completed, and Professor Johnson will 

 take up the main problem as soon as insects are available for 

 inoculation experiments. 



In the case of most insect diseases, which often serve as 

 notable checks 011 the increase of undesirable species, much 

 depends upon weather conditions, particularly upon the rela- 

 tive decrease of heat and moisture. A warm, damp season usu- 

 ally favors the development of such diseases, while a cool or 

 dry season acts adversely upon them. In the case of the gypsy 

 moth disease now being investigated, our observations so far go 

 to show that its potency depends largely upon a semistarved 

 condition of the insects. This leads to the conclusion, possibly 

 erroneous, that, if the gypsy moth colonies in the cheap scrub 

 woodland can be thoroughly isolated and prevented from spread- 

 ing, after one complete stripping of the trees has occurred the 

 disease will come in to reduce the insects below the danger 

 point. If this is proved to be the case, one of the most difficult 

 problems in connection with the moth work will have been 

 solved. 



THE FUNGOUS DISEASE OF THE BROWN-TAIL MOTH. 



In the two previous reports we have called attention to a 

 fungous disease of the brown-tail moth caterpillars, which has 

 been most effective in certain localities in holding this insect 

 in check. This disease was abundant throughout the district 

 in the summer of 1906, destroying the large caterpillars by the 

 thousands, notably in the infested white oak woodlands, where 

 nothing had been clone in the way of the applications of hand 

 methods. As a result, the numbers of moths emerging in mid- 

 summer from these woodlands was greatly reduced, and there 

 naturally followed a consequent reduction in the degree to which 

 orchards and shade trees were reinfested by the insect. 



Still later in the fall of 1906 it was found that the disease 

 had notably attacked the small brown-tail moth caterpillars, 

 with the result that in 1907, although certain localities were 

 generally infested by the moths, the condition of the entire 

 brown-tail moth district in Massachusetts was greatly improved. 



