Conspecificity of the Ticks Ixodes scapularis and I. dammini (Acari: Ixodidae)

Reciprocal crosses between Ixodes dammini</it> Spielman, Clifford, Piesman & Corwin from Massachusetts and Ixodes scapularis</it> Say from Georgia produced offspring through the F<inf>3</inf> generation when the experiment was discontinued. Reciprocal I. dammini</it> × Ixodes pacificus</it> Cooley & Kohls (California) and I. scapularis</it> × I. pacificus</it> crosses produced F<inf>1</inf> progeny; however, all progeny were sterile. Assortative mating experiments between I. dammini</it> and I. scapularis</it> indicated that males and females of both species mated with the opposite sex of heterospecific or conspecific ticks when there was a choice. Conventional discriminant analysis of morphometric measurements of ticks from Georgia, North Carolina, Maryland, Massachusetts, and two populations of F<inf>1</inf> hybrids indicated that there were recognizable differences. However, size-free (sheared) discriminant analysis indicated that these differences were largely size-dependent, with much overlap of the four eastern and two hybrid populations but no overlap with I. pacificus</it> from California. Analysis of chromosomes (morphology and C band) indicated no differences between the Georgia and Massachusetts populations but showed a difference between them and the California population of I. pacificus.</it> Analysis of isozymes showed that the genetic identity value for the Georgia and Massachusetts populations was within the normal range for conspecific populations, whereas the California population indicated congeneric but not conspecific relatedness to the Georgia and Massachusetts populations. Life cycle data collected under similar laboratory conditions showed no differences in length of feeding and molting periods among Georgia, Massachusetts, and California populations. These data and results of the work of other authors on tick host preferences and vector competence indicate that I. dammini</it> is not a valid species separate from I. scapularis.</it> Because the name Ixodes scapularis</it> Say, 1821, has priority over the name Ixodes dammini</it> Spielman, Clifford, Piesman & Corwin, 1979, I. dammini</it> is relegated to a junior subjective synonym of I. scapularis</it> (based on Article 23 of the International Code of Zoological Nomenclature).</it>