DISEASE IN CONTROL OF MOTHS. 97 



DISEASE AS A FACTOR IN THE NATURAL CONTROL OF THE GIPSY 

 MOTH AND THE BROWN-TAIL MOTH. 



In continuing this work consideration must be given to the proba- 

 ble effect which the prevalence of disease would possibly have in the 

 reduction of the gipsy moth and the brown-tail moth to the ranks 

 of ordinary rather than of extraordinary pests. In America, as is 

 generally well known, the brown-tail moth is annually destroyed to 

 an extraordinary extent as the result of an epidemic and specific 

 fungous disease, while the gipsy moth is frequently subjected to very 

 material diminution of numbers through a much less well known 

 affection popularly known as "the wilt," apparently similar to the 

 silkworm disease "flacherie." 



In more respects than one the prevalence of these diseases has 

 been inimical to the prosecution of the parasite work. In the be- 

 ginning, when it was expected that the parasites would remain in 

 the immediate vicinity of the localities where they were first given 

 their freedom, great pains were taken to provide colony sites in 

 situations where the caterpillars were not only common but where 

 there was reason to believe that they would remain healthy for at 

 least one or two years. This was an exceedingly difficult matter, 

 and one which was the cause of more troubles, doubts, and fears 

 during 1907 and 1908 than almost any other phase of the parasite 

 work. 



With the final recognition of the great superiority of the large col- 

 ony, which came about through a better knowledge of the powers of 

 rapid dispersion possessed by the parasites, this seeming obstacle to 

 success wholly disappeared, except in the case of such parasites as 

 Anastatus, which actually did remain in the spot where they were 

 placed, and which could not travel beyond a certain limited radius, 

 no matter how great the necessity. 



At the present time the association with the parasite problem of 

 the otherwise wholly separate question of disease as a factor in 

 the control of the gipsy moth and the brown-tail moth is entirely 

 confined to speculations as to the probable future of these pests, pro- 

 vided their control is left to disease alone. If, as is conceivable, 

 effective control is exerted through disease, further importation of 

 parasites is rendered not only needless but wholly undesirable. If, 

 on the contrary, such control is likely to be inefficient, from an eco- 

 nomic standpoint, every effort should be exerted to make the parasite 

 work a success. In other words, the decision as to the adoption of a 

 policy for the future conduct of the activities of the laboratory 

 depended very largely upon whether or not disease seemed likely to 

 become effective in the case of the more important of the two pests. 

 The fact that the present plans provide for the continuation of the 



95677°— Bull. 91—11 7 



