Comparisons between Populations of Typhlodromus longipilus Nesbitt and T. occidentalis Nesbitt: Taxonomy, Distribution, and Hybridization1,2

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Abstract
Significant differences in the length of peritreme and dorsal setae II were found between 8 populations designated as Typhlodromus longipilus which were collected from the midwest and northeastern regions of North America and 12 populations designated as Typhlodromus occidentalis which were obtained from western North America and the Netherlands. Individual analysis of each of 8 other anatomic features did not allow complete separation between the 2 groups; however, significant interspecific differences within each designated species were observed. Comparisons of distributions suggested that T. longipilus is common to the more humid-temperate portions of the midwest and eastern regions of North American whereas T. occidentalis is found in the more arid regions of the western United States and Canada and probably has been introduced into European glasshouses. Hybridization results gave proof of complete reproductive isolation between a T. longipilus population collected from New Jersey and each of 2 populations of T. occidentalis from central Washington state and the Netherlands. These latter 2 populations of T. occidentalis were readily hybridized and judged to be conspecific.