6 Yearbook of the Department of Agriculture. 



board, and these facts are taken into consideration in carry- 

 ing on field work -against this insect. 



The task which has fallen to the Bureau of Entomology in 

 connection with gipsy-moth control has been to use every 

 effort possible to prevent the spread of the insect and to re- 

 duce the damage resulting therefrom. It has been necessary 

 to carry through many extensive experiments in order to 

 secure information for use in the field operations, and the 

 experimental work has formed the basis and groundwork for 

 the application of field methods. Prior to 1905 no effort was 

 made to introduce the parasites and natural enemies of the 

 gipsy moth or the brown-tail moth. A popular theory exists 

 that in its native home every insect is held within reasonable 

 bounds by parasites or natural enemies, and that each insect 

 has some one species of parasite or natural enemy which is 

 responsible for its control. When this natural check fails, 

 either on account of attack by its own enemies or for other 

 reasons, the original host will, for a time, become noxious. 

 The problem of utilizing the natural enemies of the gipsy 

 moth and the brown-tail moth appeared somewhat compli- 

 cated, but the difficulties were not realized until after the 

 work was well under way. It soon became apparent that 

 neither of these pests was controlled by a single species of 

 parasite in its native home. Through the efforts of Dr. L. O. 

 Howard, Chief of the Bureau of Entomology, acting in co- 

 operation with the State of Massachusetts and many for- 

 eign entomologists, as well as numerous agents employed by 

 the bureau, a large number, approximately 30 species, of 

 parasites and natural enemies of the gipsy moth and brown- 

 tail moth have been collected and shipped to the Gipsy Moth 

 Laboratory at Melrose Highlands, Mass. Shipments of this 

 sort have been received from most of the countries of Europe 

 and from Japan. The result has been that 7 or 8 species 

 have become established in the infested area and are helping 

 to solve the problem. 



It has developed, however, that in Europe, at any rate, 

 the ravages of the gipsy moth are partially controlled by 

 several factors in addition to the work of the parasites. 

 A wilt disease which attacks the caterpillars and causes 

 heavy mortality among them is present not only there but 



