Oct. 22. I92I Hopkins Host-Selection Principle 209 



The colony was started from a small tree collected at Colorado Springs, 

 Colo., and shipped to Falls Chm'ch. This tree had been killed by Scolytus 

 in the fall of 19 16 and infested by Hylotrupes in the spring of 191 7. 



In 19 1 8 adults did not emerge until May and were caged on Douglas 

 fir to continue the colony. They were recaged on Douglas fir in 1919, 

 but all the larvae died from a fungus attacking the bark. 



HYI,OTRUP:eS WGNBUS, PSEUDOTSUGA STRAIN VIII ^ AND PSEUDOTSUGA 



STRAIN XXXV 



Two females from VIII ^ (the juniper form in Douglas fir) were held 

 in a cool cellar until adults of this XXXV variety emerged. May 29, 

 1918, they were caged on Pseudotsuga with two males from the true 

 Douglas fir form (XXXV) . The two sexes absolutely avoided each other 

 and were never observed to mate. The females died without laying 

 eggs. Many attempts were also made to mate the original juniper form 

 with the Douglas fir form but without success. 



HYLOTRUPES UGNEUS, SEQUOIA FORM. EXPERIMENT XL 



The form of Hylotrupes ligneus occurring in sequoia is slightly larger 

 but otherwise resembles that in juniper very closely, although the speci- 

 mens reared in the experiments show a much greater variety of color 

 pattern than do those from juniper. 



April 2, 1 91 8, a large series of these adults were removed from their 

 pupal cells in Sequoia sempervirens (Lamb.) Endl. and isolated in small 

 vials by F. B. Herbert at Laurel, Calif. April 13, 191 8, they were re- 

 ceived at Falls Church, Va. 



JUNIPERUS. Experiment XL ^ — Three prominent color forms were 

 paired and each was caged on a piece of juniper cut in January, 191 8, 

 since no sequoia was on hand. They all oviposited, but about half of 

 the larvae died by July. The remainder made pupal cells and emerged. 

 The strain has since been continued in juniper. 



Pseudotsuga. Experiment XL^. — April 20 one pair was caged on 

 a piece of Douglas fir cut in October, 191 7. Eggs were laid and a better 

 infestation secured than with the juniper form (VIII). All larvae died 

 and no adults were secured in the spring of 191 9. A fungus growth 

 under the bark was responsible in a large measure. 



hylotrupes ligneus, JUNIPERUS STRAIN VIII X SEQUOIA STRAIN XL 



April 13 several males from redwood (XL) were separately caged 

 with females from juniper (VIII) held over in a cool cellar since they 

 were isolated from the cells. One of these males mated with two females 

 (first and third tried) immediately on being isolated with them. This 

 same male would not mate with the second female tried, nor would any 

 males of XL mate with females of VIII. Many juniper (VIII) males 



