6 BULLETIN 250, U. S. DEPARTMENT OF AGRICULTURE. 



In the following pages are given a brief statement of the results 

 secured with each food plant tested. Field observations are also 

 included to make the data as reliable as possible. Experience has 

 shown that results, even with the same food plant, vary to some extent 

 during different years; and as the information is based upon three 

 years' work, it is believed that this variability has been given due 

 consideration. 



It should be remembered that in the trays the larvae were furnished 

 with the same species of foliage during the entire season, hence the 

 results are not exactly the same as would be secured under field con- 

 ditions where a variety of food is usually available. A certain 

 amount of injury to caterpillars always results from handling them 

 in trays, so that the rate of reproduction in the experiments is in all 

 cases less than under field conditions. 



Alder, Spreckxed (Alnus incana [L.] Willd.). 



In the tray experiments the larvae fed freely in all stages. The growth and 

 reproduction were normal. The field observers agree that gipsy-moth larva? 

 usually feed in all stages on this plant, but in the first three stages it seems to 

 be preferred. As alder is of little commercial value it should be removed when 

 cuttings are being made. (PI. Ill, fig. 2.) 



Apple (Pyrus malus L.). 



This species was found to be a favorite food of gipsy-moth larvae both in the 

 field and in the trays. In combination with other growth it is usually the most 

 heavily infested. 



Old trees of this species that have been neglected nearly always contain holes 

 and crevices in which the gipsy-moth larvae hide and go through their trans- 

 formations, the females depositing their eggs where it is difficult to find them. 

 These trees are a menace to the surrounding growth and should be removed. 



Arbor Vit^ (Thuja occidentalis L.). 



Xo observations were made on this species in the field, but it has been thor- 

 oughly tested in the laboratory. No reproduction was secured until experiments 

 were carried on with third-stage larvae. The feeding was slight and develop- 

 ment was slow and imperfect. It is an unfavored food. 



This species can be left in a stand of trees without fear of injury by the 

 gipsy moth. 



Black Ash (Fraxinus nigra [Marsh.]). 



One adult male was reared from 100 larva? started in the third stage. Many 

 other tests were less favorable to the insect. Mr. T. J. Kennedy, one of the field 

 observers, reports no feeding on this species of ash in southern New Hampshire. 

 It is an unfavored species. 



Blue- Ash (Fraxinus quadraiii/iiltitu Miehx.L 



A single specimen of this tree was under observation. It was located in 

 Klin Park, Worcester, and foliage was tested in the trays in the Worcester 

 Laboratory by Mr. Collins in 1912. 



Although larva' from the first to the fifth stages, Inclusive, were tried, none 

 reached the adult stage. It is an unfavored species. 



