Oct. 22, I92I Hopkms Host- Selection Principle 195 



OUTLINE OF EXPERIMENTS ON EACH SPECIES 

 XYI^OTRECHUS COI,ONUS. EXPERIMENT I 



Xylotrechus colonus Fab. is found in nature in a wide variety of hosts. 

 In fact, it feeds in nearly all hardwood deciduous trees of the eastern 

 and central United States. It shows little or no preference for any 

 exact condition of the wood, except that it will not attack perfectly 

 seasoned material. The larvae can be found in dying standing trees or 

 in logs felled in any month of the year provided they still contain a 

 certain amount of moisture. 



The first flight of the year occurs in the last week of May or first week 

 of June, reaching the maximum in about two weeks. A few adults 

 emerge sporadically throughout the summer. From eggs deposited in 

 June a few adults usually emerge in September, but the main brood 

 remains as larvae until the next spring. These fall adults have never 

 oviposited under confinement. 



The larvae feed entirely beneath the bark, or in the bark if it is thick. 

 The pupal cell is made in the outer sapwood or in the bark. 



The wood of all species for this experiment was cut on April 15 unless 

 otherwise stated. The colony was started by felling a red oak tree in 

 March, 19 14. The wood was attacked during that June, caged soon 

 afterwards, and the colony has since been maintained in red oak. From 

 the original oak form colonies were secured in hickory (Hicoria), chestnut 

 {Castanea dentata {M.QXsh..) Borkh.), locust {Robinia pseudacacia Linn.), 

 red maple {Acer rubrum Linn.), and ash (Fraxinus sp.), in the following 

 manner : 



QuERCUS. Experiment I. — During May, 1915, hickory logs were 

 placed in the cage with oak intended to carry on the colony. Many 

 adults were present, somewhat over 100, and the hickory as well as the 

 oak was subsequently found infested. 



In June, 19 16, in the same cage stocked with oak for continuing the 

 colony, chestnut and hickory wood was placed. There was again an 

 overabundance of adults and all woods were infested. 



In June, 191 7, oak was placed in this cage to continue the colony 

 and also ash, chestnut, locust, hickory, and red maple logs, all cut in 

 February except the hickory, which was cut in April, 191 7; extra pieces 

 of chestnut and maple, cut in November, 1916, and September, 1916, 

 respectively, were also placed in the cage. There was an abundance of 

 adults. In July these logs were examined and it was found that the oak 

 was heavily infested; the chestnut and hickory were lightly infested; 

 the ash, maple, and locust had no infestation. This same year, 191 7, 

 adults were isolated on ash (I^), maple (I*), and locust (I^) with results 

 as described in later paragraphs. 

 65583°— 21 2 



