1966] 
Nutting — Dry-wood termite 
167 
colony contained a high percentage of individuals which had ap- 
parently succumbed in large terminal chambers to drowning and 
attack by fungi, bacteria, or both. 
There is also limited evidence that Pterotermes may occupy a 
very narrow niche in this region where it only rarely comes into 
contact with other dry-wood termites. Two colonies have been 
found in wood previously or concurrently attacked by Marginitermes 
hubbardi (Banks). Marginitermes is itself a rather primitive, mono- 
typic genus which is endemic to the southwestern United States and 
western Mexico. However, from the above evidence and wider 
field experience with the latter, it is my impression that Pterotermes 
is able to occupy even hotter and dryer situations than Marginitermes. 
Comparative studies on water loss and cuticular structure (Collins 
and Richards, 1966) should provide a basis for explaining the adapta- 
tions of various species of termites to their particular environments. 
Indeed, Collins (1966, in litt.) has found that older and larger 
nymphs of Pterotermes have a comparatively low rate of water loss. 
She feels that the cuticular cement layer, which is particularly well 
developed in these forms, may be largely responsible for the ability 
of this species to conserve water and, hence, to occupy the severely 
dry environment of the Sonoran Desert. 
As a result of very inadequate collecting there are a few broad 
discontinuities in the distribution. Further field work should be 
conducted to determine whether or not this termite has an essentially 
uninterrupted distribution generally within the Sonoran Desert. It 
may actually be absent over many of the intermont plains which are 
dominated by smaller and lower plants such as Larrea and Franseria. 
However, it is a strong flier and may well be able to cross narrowed 
valleys between adjacent mountain ranges — if not in one generation, 
then in several by way of relatively isolated trees and cacti, essential- 
ly as in island-hopping. After all, it does occupy a region where 
hosts are of necessity very widely spaced. 
Host trees and nesting site. According to the meager records, 
Pterotermes has thus far been recorded nesting in the dead wood of 
only three plants: in the ribbed, woody skeletons of the giant or 
saguaro cactus, Cereus giganteus Engelm. (Fig. 2) ; one species of 
the green-stemmed palo verde tree, Cercidium floridum Benth.; and 
in the dead, flowering stalk of the non-arborescent Spanish bayonet, 
Yucca Whipplei Torr. 
In the foothill areas of the Santa Rita Range Reserve and south 
of Oracle Jet., several colonies were discovered in dead palo verdes 
of this species from which the bark had long since slipped off. A 
