14 
Indiana University Studies 
oaks, mean that Neuroterus is more specialized than some 
of its other characteristics would suggest; and yet all groups 
of white oaks are affected, rather than a single group as 
with some higher Cynipidse (e.g, Helercecus, Adleria) . Two 
black oak species, Neuroterus laurifolise Ashmead and N. 
longipennis Ashmead have formerly been included in this 
genus, but the treatment of these in the last pages of this 
paper shows that they do not belong to our present genus. 
We now know enough varieties of Neuroterus, and know 
our black oak fauna well enough to warrant a prediction 
that no Neuroterus will be found on black oaks, and that 
this genus of insects may well be used (as may other cynipid 
genera also) for recognizing the relationships of the species 
of oaks. Thus the inclusion of Quercus chrysolepis among 
the hosts of Neuroterus would further confirm the opinion 
that it is a white oak, and the exclusion of Q, Emory i and 
Q. hypoleuca, together with the infestation of these by the 
cynipids Amphibolips and the black-oak group of Plagiotri- 
chus, might definitely settle any debate as to the affinities 
of these two oaks. 
Fifty-five of the described American varieties of 
Neuroterus are restricted to single hosts, only 8 being found 
on two hosts, while none are found on more than two hosts. 
N, alhipleurse, N. nigripes, and N. opacus occur on both 
Q. stellata and Q. breviloha. 
N. irregularis and N, variegatus occur on both Q. alba 
and Q. stellata, 
N. restrictus occurs on both Q. Chapmanii and Q. Margar- 
etta. 
N. saltatorius and N. pacifietis occur on both Q. lobata 
and Q. Douglasii. 
In all these cases the two oak species concerned are rec- 
ognized to have very close affinities and occur in the same 
faunal area, which will account for the break-down in the 
ordinarily specialized sensory physiology (choice of place of 
ovi position) of the insects. 
In any single geographic region, any one oak does not 
have more than one variety of any cynipid species. This is 
true with only 4 apparent exceptions in this genus. 
N, inficiens and N. opacus occur on Q, breviloba. 
N. nigripes and N. pattersoni occur on Q, stellata. 
