202 Journal of Agricultural Research voi. xxn, N0.4 



Many adults emerged from the grape in 19 18 and five pairs were caged 

 on three small pieces of grape i}4 inches in diameter and 2 feet long and 

 one piece of hickory about the same size, both cut in Januar}^ 1917- In 

 July they were examined, and both hickory and grape were heavily in- 

 fested. 



Quantity selection. Experiment III^. — To again test out the 

 effects of host selection when an insufficient amount of wood is given than 

 that required for the number of adults present, in April, 19 18, two pairs 

 from grape were caged on grape and hickory cut in January, 191 8. The 

 piece of grape was 2 inches in diameter and i foot long, the hickory 2 

 inches in diameter and 2 feet long. An examination in July showed both 

 grape and hickory infested. 



This experiment was repeated in April, 1919, using two pieces of grape 

 and one piece of hickory, all of optimum cut and equal size. In one case 



1 pair of adults was isolated, in another case 3 pairs were used. The wood 

 on which i pair was caged contained 5 larvae in hickory and 3 larvae in 

 grape ; that on which three pairs were caged contained 4 larvae in hickory 

 and over 25 in grape. 



The grape colony was not continued in 1920. 



CONCLUSIONS 



This host variety from nature had acquired a decided preference for 

 grape. 



The selection of a host is influenced by the quantity of wood present for 

 a given number of adults, in that the adults will select a new host in 

 preference to overinfesting the original host. 



The tendency in this species in nature to confine itself to a certain host, 

 either hickory or grape, is not as marked as in some other species. 



CYIvLENE PICTUS, HICKORY STRAIN II X GRAPE STRAIN III 



In order to determine whether crossing of these two host strains would 

 influence the progeny in the selection of the host, males and females were 

 isolated from their pupal cells in the spring of 191 7. April 17 three 

 females from hickory and two males from grape were isolated in a cage 

 containing hickory. Two females from grape and two males from hickory 

 were isolated on grape. In neither case did mating occur as readily as 

 when both sexes from the same host were paired. The sexes often ap- 

 proached each other and moved away before finally copulating. 



Good infestations were secured in both cases. In April, 1918, one pair 

 from hickory was caged on equal amounts of grape and hickory cut in 

 January, 19 18. Only the hickory was infested. Two females and two 

 males from grape were isolated on the same amount of grape and hickory 

 cut in January, 19 1 8. Both woods were infested. These pieces were all 



2 inches in diameter and 1 8 inches long. 



