GENEEAL CONCLUSIONS. 41 
of that which was infested in 1905. This being the case, the oppor- 
tunity for spread has greatly increased, and as the insect gradually 
becomes established on the western slope of the high lands in the 
central part of the State, the opportunity for serious damage in 
the Connecticut valley is rapidly increasing. 
In connection with the weather record given for this period it is 
interesting to note the corresponding data from the Weather Bureau 
stations at Portland, Me., and at Concord, N. H., as these data have a 
bearing upon the spread in the northern part of the territory. 
GENERAL SUMMARY. 
The map and wind direction records give a fairly good idea of the 
dispersion of the gipsy moth. The spread has been along the lines of 
the prevailing winds to so great an extent that the evidence is con- 
clusive that natural spread is accomplished chiefly in this way. All 
the records bear out this conclusion. It should be noted in the Con- 
cord records that the southeast winds were the ones Avhich were most 
likely to carry the larvae into new territory, while in Portland the 
south and west winds which predominated would do the same thing 
in that section. It should be remembered that neither Concord, N. H., 
nor Portland, Me., has been badly infested and that the spread must 
come from bad colonies nearer the center of infestation. 
The general " seeding down " of slightly infested territory by 
larva? spread by the wind is shown in some detail in the following 
pages. 
GENERAL CONCLUSIONS. 
It is impossible to give a detailed explanation of the cause of every 
infestation. The weather records give strong evidence that the wind 
is responsible in a large degree for the spread of the gipsy moth, but 
the spread can be brought about only under the favorable conditions 
which have already been explained. The present apparatus for 
recording wind movements is somewhat imperfect, and as the wind 
is usually very variable it is probable that a greater local spread 
results than can be explained from wind records. Other things being 
equal, wind spread will start the most vigorous colonies nearest the 
bad centers of infestation, 1 for the farther the caterpillars are carried 
the more chance there is for them to become widely separated, so 
1 On May 19, 1912, Mr. C. W. Stockwell found that large numbers of first-stage gipsy- 
moth larvae that hatched a few days before were being blown from an isolated block of 
birches into a pasture by a strong southwest wind. At a point 125 feet from this block 
he found from 21 to 27 larva? per square foot ; they were crawling about on the grass 
seeking food. On the posts of a wire fence, 185 feet from the birches, over 500 larvae were 
found on each post, and smaller numbers of larvae were found at a greater distance 
away. This substantiates the experiments previously made, and shows what happens 
in nature under favorable conditions. It also proves that the heaviest infestations 
brought about by wind spread will be nearest the colony from which the larvae were 
spread. 
