190 Journal of Agricultural Research voi.xxn.No. 4 



Examinations made this season, 1913, show a still greater reduction in the infesta- 

 tion; in fact, the infestation is so light tliat it is actually less on the treated areas 

 than it is throughout any other area on this Forest. 



and — 



There was no reoccupation of the treated areas by broods from the lodgepole infested 

 trees at higher elevations. 



and by Hofer — 



As we reached the summit near the North Powder Peaks we attained an altitude of 

 8,000 feet; the elevation at the Sheep Ranch is about 4,000 feet. From the summit 

 of this divide for a distance of 10 miles north, 10 miles east, and 16 miles west we 

 noted heavy infestation, both old deadings and the new work also, in both the lodge- 

 pole pine and white bark pine, especially on both slopes of Antone Creek. 



No new infestation was found on the treated areas on Anthony Creek, Camp area. 



This seemed to furnish substantial evidence that the principle would 

 hold. 



The principle as defined by Dr. Hopkins ^ is that an insect — 



species which breeds in two or more hosts will prefer to continue to breed in the host 

 to which it has become adapted. 



In order to secure further evidence relating to this principle, the writer, 

 after consulting with Dr. Hopkins, began a series of experiments in 19 14 

 with insects which infest two or more species of wood. The wood-boring 

 Cerambycidae, or long-homed beetles, offered material which was very 

 well adapted to the conduct of such experiments. Many species were 

 easily available which exhibit great diversity in their selection of hosts 

 in nature, as illustrated by those breeding exclusively in a single species 

 of plant and those apparently attacking almost any wood. This varia- 

 tion in host habits at once brought up the following questions : Will those 

 species confined to a single host live in any other, and do the individuals 

 coming from a certain plant of those species breeding in a variety of hosts 

 select the same species of plant on which to oviposit ? Again, if such is 

 the case, how do these host strains originate in nature? 



As these experiments progressed new problems came up demanding a 

 broadening of the experiments from- year to year until, during the season 

 of 1918, over 100 individual experiments were in progress. Fourteen 

 species of insects and 21 species of plants were used, combining to form 

 45 host strains. It was thought desirable to conduct experiments on 

 more species rather than more intensive experiments on a few species. 

 It will be noted that certain experiments were not carried as far as others, 

 due to the fact that time was not available or due to the absence of the 

 writer at the critical time. At present several points remain to be con- 

 clusively settled, and investigation of these will be continued another 

 year or so. Nevertheless it is believed that sufiicient data have been 

 accumulated to show definitely the extent to which the influence of the 

 host applies to these insects. 



1 Hopkins, A. D. economic investigations of the scox,ytid bark and timber beetles of north 

 AMERICA. In U. S. Dept. Agr. Program of Work, 1917, p. 353. 1916. 



