GIPSY MOTH AND BROWN-TAIL MOTH. 7 



trains, horse-drawn vehicles, or automobiles. The danger of such 

 spread is very limited if the roadways are kept free from severe 

 infestation, and under present conditions in the infested territory 

 danger of spread in this way is not great. New colonies are started 

 principally by the spread of newly hatched caterpillars. Experiments 

 have shown that under favorable conditions these caterpillars may 

 be blown by the wind. The temperature must be high enough for 

 the caterpillars to be active and the stronger the wind the greater 

 the probability of their being carried long distances. It has been 

 demonstrated that caterpillars have been carried more than 20 miles 

 in this way, and specimens have been caught in the air 50 feet above 

 the ground, although probably they are carried much higher than 

 this. It is necessary for the temperature to range above 65 F. and 

 for the wind velocity to be 8 miles or more per hour, in order that 

 wind spread of small caterpillars may result. 



FOOD PLANTS. 



The food plants most favored by the gipsy moth are the apple, the 

 different species of oak, gray birch, alder, and willow. In cases of 

 bad infestation nearly all deciduous trees are injured to a greater or 

 less extent, with the exception of ash. Hickory is not a favored food 

 plant, although the foliage occasionally shows severe feeding. Chest- 

 nut will not support the gipsy moth when the caterpillars are in the 

 first stage, and pine will not support the first two stages; but -if other 

 food plants are present severe injury may result from feeding by the 

 larger caterpillars. Beech is sometimes fed upon freely, and occa- 

 sionally the trees are defoliated ; and the same is true of poplar. 



INJURY CAUSED BY THE GIPSY MOTH. 



Unless reduced in numbers by natural enemies, or by the applica- 

 tion of control measures, the gipsy moth is capable of causing enor- 

 mous injury to tree growth. In the area in New England which has 

 suffered most from this insect thousands of trees are dead as a result 

 of defoliation. (See fig. 3.) Many areas were cut before the trees 

 were mature and the wood sold at a loss on account of damage caused 

 by this insect. Apple and oak have been injured most, but pine and 

 other coniferous trees mixed with deciduous growth have suffered 

 severely. 



It is undoubtedly true that many oak trees which have been weak- 

 ened severely as a result of defoliation by the gipsy moth and the 

 brown-tail moth have failed to recover because of the attacks of cer- 

 tain wood-boring insects. The species which has caused most damage 

 in this way is a beetle l known as the two-lined chestnut borer, the 

 larva of which feeds beneath the bark of injured trees. 



1 Agrilus bilineatus Weber. 



