oct.22, I92I Hopkins Host-Selection Principle 213 



forms, but only about half the brood emerges at the end of the first year, 

 the remainder going over in the larval stage to the following season. The 

 adults emerge about a month earlier, April i to 10. 



Infested hackberry branches from Hummelstown, Pa., were collected 

 and sent to Falls Church, Va., in December, 1915, by J. N. KnuU. 



In April, 19 16, 20 adults were caged on January cuts of hackberry, 

 dogwood, and redbud, but only the hackberry was attacked. 



In April, 191 7, eight adults were isolated on sticks of redbud, dogwood, 

 and maple, all cut in September and November. No eggs were laid in 

 any of these woods. The form has since been continued in hackberry. 



CONCLUSIONS 



A very decided predilection for the original host is exhibited by the 

 host strains of this species. It is not surprising in the case of the hack- 

 berry form, as this is the only host from which it has been found. How- 

 ever, this form would not even lay eggs on any hosts other than the 

 original. In the dogwood strain adults were not isolated on maple alone, 

 nor were adults of the maple strain isolated on dogwood alone. If this 

 had been done, it is veiy likely that infestations would have resulted. 



NEOCIvYTUS ERYTHROCEPHAI^US. EXPERIMENTS XI, XII, AND XIII 



The adult and larva of Neodytus erythrocephalus Fab. are quite different 

 from those of Neodytus capraea, but the range and habits are much the 

 same. The species attacks wood in a greater variety of conditions, but 

 the most favorable condition is an early spring cut. It has been collected 

 in almost all eastern hardwoods. 



The first flight occurs at Falls Church, Va., in late May or early June; 

 consequently, that the wood may be sappy for infestation it must be 

 cut during April. The species overwinters in the larva stage, pupation 

 not taking place until early April. Farther south two or more genera- 

 tions occur each season. 



Three host strains were collected in nature and experimented with. 



NEOCLYTUS ERYTmiOCEPHALUS, HICORIA FORM. EXPERIMENT XI 



June 9, 19 16, adults emerging from hickory at Falls Church, Va., were 

 recaged on wood cut in late March. A good infestation was secured. 



June 8, 191 7, the colony was continued in April cuts of hickory. Two 

 pairs were isolated in a cage containing hickory and redbud cut in April 

 and dogwood and tulip {Liriodendron tulipifera Linn.) cut in May. In 

 July an examination showed hickory to be the only wood infested. 



May 23, 19 18, two pairs were isolated on hickory, dogwood, and redbud 

 cut on April 15. When examined on July 18 hickory was found to be 

 lightly infested, dogwood heavily, and the redbud contained no larvae. 



May 24, 19 18, six pairs of adults were caged on two pieces of hickory 

 and one of dogwood, cut April 15, of the same size as those of the 



