30 THE DISPEESION OF THE GIPSY MOTH. 
dying. The tests were carried on under laboratory conditions which 
were unfavorable to the insects. 
During the winter of 1911-12 a few experiments of the same sort 
were tried at the gipsy-moth parasite laboratory, and records rang- 
ing from 31 to 138 feet have been secured. The conditions for 
making the tests were very unsatisfactory, and it is probable that 
newly hatched larva?, without food, would be able to crawl, on the 
average, about 100 feet in the open before death would ensue. This 
does not give the maximum distance that the majority of larva? 
could crawl, because many of them in going that distance would find 
some foliage which could be eaten and thus would be enabled to 
proceed farther. 
DEGREE OF INFESTATION. 
The degree of infestation has an important bearing on dispersion. 
W nen only a few egg clusters are present on a tree the larvae have 
plenty of food, and it is not necessary for them to move about so 
actively. As the infestation increases the feeding conditions become 
more crowded, and, as a result, the larva? are disturbed and large 
numbers of them spin to the ground. In badly infested places the 
air is sometimes well filled with a network of silken threads, which 
are made by larva? spinning to the ground (PL XII), and it is 
possible to see large numbers of them hanging from the trees. 
These conditions favor dispersion by the wind. 
KINDS OF FOOD PLANTS. 
At the time the gipsy moth first became noticeable in this country 
and caused so much damage, it seemed almost impossible to find 
plants upon which it would not feed. Many experiments were 
carried on with fifth and sixth stage caterpillars, which were fed in 
glass jars upon various kinds of foliage, and very few plants were 
rejected, especially if the insects were supplied with no other food. 
The results of these experiments were published by Forbush and 
Fernald in 1896. Since that time it has become gradually more 
noticeable that the larva? show marked preference for certain species 
of trees. This may be due to a gradual change of habit, or to the 
fact that caterpillars which do not find food which is most suitable, 
although they may strip and injure the tree, may not come through 
to maturity. 
There is considerable difference in food requirements of the small 
and the large caterpillars of this insect, the former not being able 
to survive on some species of trees upon which the larger ones will 
feed. The white pine is one of the trees of which this may be said, 
and it has been repeatedly demonstrated that the first-stage larva 4 can 
