Oct 22, 1921 Hopkins Host-Selection Principle 201 



11^^. — To test the influence of an overabundance of adults and scarcity 

 of the primary host on the host selection. Three pairs of adults from 

 hickory were caged on a small piece of grape and a small piece of hickory 

 (each 2 inches in diameter and i inch long), each cut during January, 

 19 1 8. Examination in July showed both woods to be infested, the grape 

 containing a few more larvae than the hickory. 



In 1920 no adults emerged. 



II, 11^. — In 1920 only two strains were continued, those in hickory and 

 those in mulberry. No attempt was made to reestablish the others that 

 failed. 



CONCLUSIONS 



This species, although most commonly found in hickory, will readily 

 adapt itself to several other plants, notably mulberry and grape, both of 

 which are recorded as natural hosts. 



In some unfavorable hosts, or in an optimum host hi an unfavorable 

 condition, the larvae may become established, but the mortality is high 

 and the progeny seem to be sterile. 



After one year's feeding in a new host the larvae may select that host in 

 preference to others. 



The selection of a host is influenced by the number of adults present 

 and the quantity of the primary host, in that adults will prefer a sec- 

 ondary host to overinfesting the original host. 



The selection of a host is influenced by the condition of the host, a 

 favorable condition of secondary host being preferred to an unfavor- 

 able condition of the original host. 



The optimum condition of any host capable of properly supporting 

 growth of the larvae is of very restricted limits. 



CYI,I,ENE PICTUS, GRAPK HOST STRAIN. EXPERIMENT III 



This is the same species as previously discussed, having the same 

 biological habits except that this host strain in grape (Vitis) was taken 

 in nature at Hummelstown, Pa., in January, 1916, by J. N. Knull. 

 Since then the colony has been continued at East Falls Church, Va., in 

 grape cut in January or February. Other host strains have been pro- 

 duced and experiments conducted as follows : 



HicoRiA. Experiment III ^ — When these adults emerged from 

 grape (May, 19 16), three females and two males were isolated in a cage 

 containing 10 pieces of grape and i piece of hickory cut in February, 19 16. 

 No eggs were laid on the hickory. April 17, 191 7, two pairs of adults 

 were isolated on hickory cut in January, 19 17. Eggs were laid and the 

 larvae developed but not so rapidly as in the grape. June 15 they were 

 under normal size. By September only two larvae were alive. One of 

 these pupated but died during the winter. 



