Taxonomic status of Ixodes didelphidis (Acari: Ixodidae)

Abstract

Ixodes didelphidis Fonseca & Aragao was described in Brazil in 1952 as a new tick species that differed from Ixodes loricatus Neumann by the spiracular plate pattern. We have reared four tick colonies from different geographic areas in the laboratory that were started from single engorged females originally identified as I. didelphidis (BMG colony) and I. loricatus (CSP, PSP, and TRJ colonies). We analyzed the spiracular plate morphology of F1 adult ticks from each tick colony, compared their biological data, and performed a molecular analysis of the second internal transcribed rDNA spacer (ITS2) to test the validity of the species I. didelphidis. The spiracular plate analysis of laboratory F1 adult ticks yielded from single females from the four colonies showed variations that invalidate morphological parameters for differentiation of I. loricatus and I. didelphidis. Biological data of the BMG, CSP, and TRJ colonies were similar. The biology of the PSP colony was not evaluated. The ITS2 sequence variations observed between the tick colonies ranged from 1.3 to 4.9%, and the similarity tree constructed by the neighbor-joining method with nucleotide distances showed that the distances between the samples were similar to what is expected for intraspecific variations found in other ticks species. The morphological and biological results, in conjunction with the ITS2 analysis, supported the conspecificity of I. loricatus and I. didelphidis.