GIPSY MOTH AND BROWN-TAIL MOTH AND THEIR CONTROL. 23 
when the gipsy moth caterpillars are hatching in the spring. It has 
been proved experimentally that the caterpillars, immediately after 
hatching, can be blown long distances, and of course such spread is 
very difficult of prevention. Fortunately the caterpillars must be 
active or they will not be caught up by the wind, and no activity is 
possible unless the temperature is high. From this it results that 
‘most of the wind spread is toward the north and northeast, so that the 
danger of spread by wind to territory outside of New England is not 
serious at present. 
The work of the bureau is being carried on along several distinct 
lines, namely, experimental work, silvicultural investigations, quaran- 
tine work, and scouting work. The experimental work is conducted 
for the purpose of obtaining information which will serve as a basis 
for better control methods. It includes a thorough study of the food 
plants of the insects concerned and of the feeding habits of the cater- 
pillars in their different stages, the rate of increase in the field, the 
means by which the insects are spread, the introduction and distribu- 
tion of the foreign parasites and natural enemies of these species, and 
a study of the wilt disease, which has now become a prominent factor 
in reducing the infestation in many localities. The last investigation 
is being carried on cooperatively with the Bussey Institution of 
Harvard University, and Dr. W. M. Wheeler, who has charge of the 
economic entomology in that institution, is supervising the technical 
aspects of the work. A study is also being made, in cooperation with 
Dr. A. D. Hopkins, who has charge of the Forests Insect Investiga- 
tions of this bureau, of the secondary insects which attack defoliated 
trees. 
Silvicultural investigations are being carried on in cooperation 
with the United States Forest Service. Mr. G. E. Clement has been 
assigned from that service to this bureau for the purpose of conduct- 
ing experiments to determine whether better silvicultural practices 
and improved methods of forest management can be employed as a 
help in checking the spread of these pests. 
The entire infested area—15,235 square miles occupied by the gipsy 
moth and 32,420 square miles occupied by the brown-tail moth—has 
been placed under quarantine by the Federal Horticultural Board, 
and shipments of nursery stock, lumber, cordwood, and other forest 
products are not permitted to leave the territory unless they have 
been inspected and are accompanied by a certificate stating that they 
are free from infestation. This work is designed to prevent the 
spread of the insects for long distances and is being administered by 
Mr. D. M. Rogers. 
The scouting work consists in making examinations in the towns 
outside the infested area and is directed by Mr. L. H. Worthley. This 
