14 BULLETIN 204, U. S. DEPARTMENT OF AGRICULTURE. 



in order to establish the essential facts concerning the identity of 

 the organism and the conditions most favorable for its increase and 

 development. 



FOOD-PLANT INVESTIGATIONS. 



As has already been pointed out, the species of tree growth have 

 an important relation to the ability of the gipsy moth to increase 

 and cause serious damage in the field. Nearly 20 years ago food- 

 plant experiments were conducted in this country to determine the 

 species upon which the gipsy moth would subsist, and a long list of 

 food plants was published by Forbush and Fernald hi their excellent 

 book on the gipsy moth. Most of these experiments, however, were 

 carried on by using large caterpillars and feeding them in jars or cages 

 in the laboratory. At that time it did not seem important to deter- 

 mine whether there was variation in the feeding habits of the cater- 

 pillars in different stages. As early as 1908 it was observed and 

 proven by an extensive field experiment that the first-stage cater- 

 pillars of the gipsy moth could not develop on white pine in the 

 absence of other food. This naturally led to the question of unfavor- 

 ability of other species to gipsy moth attack. In 1912 a careful 

 series of food-plant experiments was begun. Mr. F. H. Mosher took 

 charge of this work and has been furnished with a number of assist- 

 ants during the feeding season. The feeding was carried on in indi- 

 vidual trays, which were specially constructed for the purpose. 

 One hundred first-stage caterpillars were placed upon a branch of 

 foliage in each tray. In this way the f eeding habits could be observed, 

 the foliage renewed daily, and it was possible to determine which 

 food plants were least subject to attack under laboratory conditions. 

 Similar experiments were carried on with caterpillars in the succeed- 

 ing stages. This work was continued in the summers of 1913 and 

 1914, so that up to the present time about 250 species of trees and 

 shrubs have been tested. 



As a result of these experiments some of the more common species 

 are rated as follows: 



I. — Species favored by the gipsy-moth larvae in all stages: 



Alder, speckled. 1 



Ash, mountain. 1 



Aspen. 1 



Balm of Gilead. 1 



Basswood. 



Beech. 



Birch, gray. 1 



Birch, paper. 



Birch, red. 1 



Boxelder. 1 



Larch . 



Oak, "black. 



Oak, chestnut. 



Oak, post. 1 



Oak, red. 



Oak, scarlet. 



Oak, swamp white. 



Oak, white. 



Poplar, big toothed. 1 



Shadbush. 1 



Willow. 1 



Witch hazel. 1 



1 Species of low commercial value. 



