Oct 23, 1931 Hopkins Host-Selection Principle 207 



April 17, 19 1 8, the first adult emerged from this cross. The second 

 adult emerged April 25. May 3 and 4 eight adults emerged. All the 

 19 1 8 adults resembled the juniper form in color. These adults were all 

 isolated in a cage containing juniper and pine cut in November, 19 17. 

 An examination in July showed only the juniper to be infested, but by a 

 very light brood. During the remainder of the summer all died except 

 three larvae which constructed pupal cells. May 5, 19 19, two males and 

 one female emerged and one pair was caged on juniper cut in November. 

 A light infestation occurred. May 12, 1920, five adults emerged and 

 were recaged on juniper. The selection of pine and juniper was not 

 again tested. t;"- ,.,) hf>q<f:?" 



IV X V. — ^These same species were mated in 19 17 by making the recip- 

 rocal cross (males from juniper and females from pine) and caged on 

 pine. The sexes did not mate readily, not noticing one another for some 

 hours after being caged together. However, several matings finally took 

 place and eggs were laid on the pine. Young larvae developed but all died 

 later. The same experiment was repeated in 19 18 with the same results. 

 Conditions were similar to those in the previous experiment. 



CONCLUSIONS 



The crossing did not influence the selection of a host in the first genera- 

 tion of resulting adults. 



These two forms, even though they may be crossed successfully, should 

 be regarded as distinct species based on adult characters and biological 

 differences. 



The successful cross-mating produced progeny in the first generation 

 that emerged over the period of emergence of both parents — a few early 

 when the pine form emerges, the remainder some two weeks later when 

 the juniper form appears. In later years they emerge as the juniper 

 form. 



The juniper color pattern of the adults is dominant. 



HYLOTRUPES UGNEJUS, JUNIPEIR FORM. EXPERIMENT VIII 



The adult forms generally included under Hylotrupes ligneus Fab. show 

 a great variation of color patterns. Many of these varieties have been 

 described as distinct species by Col. T. L. Casey. In the experiments 

 conducted all color varieties, however, have been kept distinct only 

 by the host in which they were found in nature and not by the color 

 variations. The experiments were primarily conducted to test these 

 variations in color patterns, but certain results bearing on the host- 

 selection principle were obtained and are here described. 



Hylotrupes ligneus, juniper form, has a wide selection of hosts. Speci- 

 mens in the Forest Insect Collection of the Bureau of Entomology have 

 been recorded from all genera of coniferous trees indigenous to North 

 America. It uniformly prefers wood that has not seasoned a great deal. 



