18 BULLETIN 204, U. S. DEPARTMENT OF AGRICULTURE. 
natural enemies were also made and from time to time collections of 
egg clusters or caterpillars near the points were obtained and sent 
to the laboratory in order that the percentage of parasitism might be 
determined. This work should be continued in order to determine 
whether after the natural enemies become firmly established the 
outbreaks of this insect will be periodical over a large territory or 
whether, as is the case at the present time, the smaller colonies will 
increase so that stripped areas will be found scattered over the entire 
region. 
DISPERSION WORK. 
For the past three or four years considerable attention has been 
paid to the means by which the gipsy moth spreads. As the female 
moth does not fly it is apparent that the dispersion of the species 
must be very slow unless it is carried by other means. Egg clusters 
may be transported on lumber, forest products, Christmas trees, 
or other material which is likely to be shipped long distances from the 
infested area. This matter has been given careful consideration and 
means have been taken to prevent the spread of the moth in this way. 
Information concerning methods used are given under the quarantine 
part of this report. 
In the spring of 1910 a number of experiments were conducted which 
showed that first-stage gipsy-moth caterpillars may be carried by the 
wind, and the information secured at that time has been published. 1 
Since this work was carried on more elaborate experiments have 
been conducted by Mr. C. W. Collins and assistants, to obtain long- 
distance records on the spread in this manner. A study has also been 
made of the likelihood of the insect being spread by caterpillars drifting 
in streams, or by wood or other material which is infested with egg 
clusters floating in rivers and becoming lodged in territory which was 
not infested. At present wind spread seems to be the chief natural 
means by which the insect becomes established in new territory. 
The trend of the spread is toward the north and northeast on account 
of the fact that the warm prevailing winds before the first of June, 
when the caterpillars are in the first stage, usually blow in those 
directions. This has resulted in a large increase in the area infested 
in Maine, and the territory in that State will probably continue to 
extend as long as large areas are seriously infested in New Hampshire 
and Massachusetts. The western spread of the insect has probably 
been greatly retarded by reason of the fact that low temperature, 
causing the caterpillars to be inactive, has prevailed when the 
winds came from the east or northeast. Heretofore serious infesta- 
tion did not occur in southeastern Massachusetts or Rhode Island; 
hence winds from the southeast were not an important factor in 
1 Burgess, A. F. The dispersion of the gipsy moth. U. S. Dept. Agr., Bur. Ent., Bui. 119, 62 p., 16 
pi., 6 fig., 1 map, Feb. 11, 1913. 
