198 Journal of Agricultural Research voi. xxn. no. 4 



The number of insects present under identical conditions influences 

 their selection of hosts. When few are present they concentrate on 

 original or favored hosts; when more than can successfully oviposit on 

 original hosts are present, less favored hosts are taken. 



CYIvI,ENE PICTUS, HICKORY HOST STRAIN. EXPERIMENT II 



The larvae of Cyllene pictus feed almost exclusively in hickory. A few 

 specimens have been taken in wild grapevine (Vitis sp.), mulberry {Moriis 

 rubra Linn.), osage orange (Toxylon pomiferum Raf.), and hackberry 

 {Celtis occidentalis Linn.), but such instances are rare and of very local 

 occurrence. In one locality near Harrisburg, Pa., all except one of these 

 unusual food plants have been recorded. This borer is found generally 

 distributed east of the Mississippi River. The optimum condition of 

 wood is that cut during the winter, preferably in January, and left lying 

 on the ground. November cuts are sometimes attacked, but no wood is 

 suitable unless the inner bark is still sappy. Sticks cut at the time of 

 emergence are too green for attack. 



The first emergence occurs about the middle of April and continues 

 for three weeks. By September the larvae are full grown and have con- 

 structed their pupal cells in the wood. They soon pupate, and in this 

 stage they overwinter. The larvae feed about equally beneath the bark 

 and in the wood. 



These experiments were started in April, 19 15, when adults were 

 found ovipositing on a hickory log cut during the winter at Falls Church, 

 Va. The strain has since been continued in January and February cuts of 

 this wood, and other host strains have been attempted with varying suc- 

 cess in grape {Vitis sp.), locust (Robinia pseudacacia) , ash {Fraxinus sp.), 

 and mulberry {Morus rubra). Experiments were conducted as follows: 



ViTis. Experiment II ^ — In April, 1917, a piece of grape, cut in 

 January, was placed in the same cage with much hickory used for the 

 continuation of the hickory form. This grape was not infested. 



June 26, 19 1 7, sixteen larvae, about half grown, were transferred from 

 hickory to grape cut in January. Nearly all these larvae lived, and the 

 following spring 12 adults emerged. They were isolated in a cage con- 

 taining several pieces of grape and one of hickory, both cut in February. 

 Examination in June showed the grape to be heavily infested while the 

 hickory contained no larvae. 



In April, 191 8, a large number of adults emerged from the grape. 

 Two pairs were isolated in a cage containing one piece of grape 2 inches 

 in diameter and 2 feet long, and one piece of hickory of the same size, 

 both cut in January. Examination in July showed the grape to be very 

 heavily infested, whereas the hickory contained only a few larvae. 



Robinia. Experiment II ^ — April 21, 191 7, three females and two 

 males from hickory were caged on a piece of locust cut a month pre- 

 viously. The females laid all their eggs on the locust and the young 



