Host-associated differentiation in the plum rust mite Aculus fockeui (Acari: Eriophyoidea) revealed through molecular and morphometric analyses.

Aculus fockeui (Nalepa and Trouessart) is among the most economically significant pest mite species within the superfamily Eriophyoidea. In traditional taxonomy, A. fockeui was considered a single, oligophagous species, initially described on European plum and later reported on around 17 plant species within the genus Prunus. Cryptic speciation is common on eriophyoid mites with a small, morphologically simplified body. Given the limitations of conventional taxonomic methods in resolving cryptic species, integrating morphometric and molecular data is essential for accurate differentiation. Fifteen populations of A. fockeui collected from five different host plant species were analyzed using morphometrics in combination with the nucleotide sequences from the mitochondrial COI gene and the nuclear D2 region of the 28S rDNA. The results of both morphometry and molecular analyses were consistent and supported the hypothesis that the A. fockeui complex comprises multiple cryptic lineages. The substantial divergence in mtCOI sequences, compared to the considerably lower variability in the nuclear 28S D2 region, indicates a relatively recent evolutionary divergence among these lineages. The results obtained in this study support the hypothesis that A. fockeui represents a complex of cryptic species.