The Genus Amblyomma (Ixodidae) in the United States

Abstract

The publication of a review of the genus Amblyomma in the United States has become desirable because of the increasing interest in the members of this genus as known or suspected carriers of diseases and especially because of the need for criteria for the specific differentiation of the larvae and nymphs. This genus, which is far richer in species than any other, is geographically limited to that portion of the world which is between the 40th parallels of latitude, that is, to the warmer countries. In the United States it is essentially limited to the Southeastern and Southcentral States. C. L. Koch (1844) was the first to publish a comprehensive account of the ticks. He described many new species and the genus Amblyomma. Though he laid the foundation for the systematic classification of ticks, he failed in many instances to select adequate characters. G. Neumann in 1896 began his Revision de la Famille des Ixodes which included Amblyomma and he was the first to use satisfactory morphological characters and thereby made a definite contribution to the classification of genera and species. Donitz (1909) urged the importance of the ornamentation as an aid in recognizing the species and his plan of giving names to the constituent spots and stripes brought order into the terminology of the ornate pattern which most species of Amblyomma display. However, the species of Amblyomma in the United States are readily separated by morphological characters, hence the ornate color patterns are not described in this paper. They are shown in the figures. L. E. Robinson (1926) gives excellent descriptions and figures of the 86 species then known and also summarizes their geographical distribution, hosts, economic aspects, and relation to disease. The more important later writings include Sharif (1928), Dunn (1934), Aragao (1936) and Osorno-Mesa (1941). Other contributions have been made by Warburton (1927), Schulze (1932, 1933, 1936), Kishida (1935) and Cooley and Kohls (1942). The collection of the Rocky Mountain Laboratory now contains 65 described species of Amblyomma from various parts of the world. A study of these and of other available species has led to a fuller understanding of critical morphological and color characters as well as of variation. Variation occurs, particularly in the color patterns, but is less confusing than in some other genera. A single male specimen of Amblyomma ovale (Koch, 1844) taken from a dog, Sept. 8, 1941, Tama Indian Reservation, west of Tama, Iowa, was sent to us for