153 
THE BIOLOGY OF SOME NORTH AMERICAN 
TICKS OF THE GENUS DERMACENTOR\ 
By F. C. BISHOPP and H. P. WOOD, 
Of the Bureau of Entomology, United States Department of Agriculture. 
(With Plates X to XII, and 1 Map.) 
No group of ticks presents a more interesting biological study than 
the genus Dermacentor. The diversity of habits of these ticks is 
remarkable. These differences in habits, especially when we find them 
correlated with certain structural characteristics, would lead some to 
consider splitting the genus into two or more genera or subgenera. 
This we do not think well advised. 
In North America we find more species of the genus Dermacentor 
than in any other part of the world, there being at least eight valid 
species' 1 2 and one variety. The species of the genus may be divided into 
two groups, based on their habit of moulting on or off the host. 
The group which moults on the hosts is composed of nitens, 
nigrolineatus and albipictus. Dermacentor nitens shows the highest 
specialization in habits. It attaches itself almost exclusively in the ears 
of the host and has a limited host relationship. This species has 
circular stigmal plates with a few large goblets, and it is devoid of 
white marking in both sexes. D. nigrolineatus has oval stigmal plates 
(PI. X, fig. 9 f ; fig. 8 $) with only a suggestion of a postero-dorsal 
prolongation and comparatively few (many more than nitens) large 
goblets ; it is also unmarked with white. D. albipictus (PI. X, fig. 5 </; 
fig. 6 ? ) has larger goblets than nigrolineatus, and the stigmal plates 
1 Published by permission of the Chief of the Bureau of Entomology. 
2 We are in doubt about the status of Dermacentor salmoni Stiles (Bull. 62, Hygienic 
Lab., U.S. Pub. Health and Marine Hospital Service, pp. 55-60, 1910), but are inclined to 
regard it as but a variety of D, albipictus Packard, 
Parasitology vi 
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