Oct. 22, 1921 Hopkins Host-Selection Principle 199 



larvae bored through the bark, but by the middle of June all had died. 

 June 15, twelve larvae 5 mm. long were transferred to locust and these 

 all died by July 11, when three more, over half grown, were transferred. 

 These lived to construct pupal cells and pupated, but all the pupae died 

 during the winter. 



In April, 1918, five adults (three females and two males) from hickory 

 were caged on locust cut during January, 19 18. The females laid all 

 their eggs, but only a few larvae lived. These constructed pupal cells 

 and pupated beneath the bark. In locust the larval mines are not 

 normal, lying in almost all cases immediately beneath the bark instead 

 of extending deep into the wood. About half the larvae made pupal cells 

 in the outer sapwood while the others pupated beneath the bark instead 

 of, as normally, deep in the wood. 



April 20, 19 19, a total of six adults had emerged and two pairs were 

 caged on pieces of locust and hickory cut in January, 19 19. An exami- 

 nation July 16 showed no infestation in either. 



Fraxinus. Experiment II ^. — April 24, 191 7, three females and two 

 males were isolated on ash cut during January. The females laid all 

 their eggs and the young larvae bored through the bark, but all died 

 before June 15. At this time fourteen larvae 5 to 7 mm. long were trans- 

 ferred to the same ash, and all died within a month. July 15, five more, 

 over half grown, were transferred. They mined extensively beneath the 

 bark, but all died before the end of September without pupating. 



July 24, 19 18, fifteen larvae, one-half to three-fourths matured, were 

 transferred to ash cut in January. 



April 21, 19 19, a total of eight adults had emerged. One pair was 

 caged on the January cut of ash, and two pairs were caged on January 

 cuts of ash and hickory. 



July 16 the wood was examined, but in no case was it infested. 



MoRUS. Experiment II*. — April 29, 1918, three females and two 

 males from hickory were caged on mulberry cut in January. The females 

 laid eggs, and a very heavy infestation was secured. They developed 

 normally and suffered little more than the normal rate of mortality 

 experienced in hickory. 



April 21, 19 19, a total of 17 adults had emerged; two pairs were trans- 

 ferred to a cage containing two pieces of mulberry and one piece of 

 hickory cut during January, 19 19. In another cage containing the same 

 quantity of wood four pairs of adults were transferred. In neither case 

 was the quantity of mulberry sufficient to permit the development of 

 all the larvae. Each piece was 2 inches in diameter and 14 inches long. 



July 16 the cages were examined, and that containing two pairs of 

 adults was infested as follows: Hickory 6 larvae, mulberry over 30; 

 that containing four pahs, hickory 13 larvae, mulberry very heavily in- 

 fested, over 40. 



