Towards Solving the “Colomerus vitis Conundrum”: Genetic Evidence Reveals a Complex of Highly Diverged Groups with Little Morphological Differentiation

Abstract

Colomerus vitis is a pest of grapevine worldwide that includes three strains recognised by plant symptoms (bud, erineum, and leaf curl), which could represent cryptic species. We approached this long-standing question by integrating genetic and morphological methods. COI sequences of mites from South Africa and other countries showed five phylogenetic groups (G1 to G5) with intergroup p-distances up to 23% and intragroup divergence lower than 2%. The three groups found in South Africa (G1, G2, and G3) were screened from a variety of grapevine samples using a novel multiplex PCR method. Only G1 and G3 were significantly associated with erinea and buds, respectively, and the three groups were frequently co-present in the same plant sample. Cryo-SEM showed adults with five- and six-rayed empodia, variable microtubercle shape, and prodorsal shield patterns. Specimens with six-rayed empodia and a smooth prodorsal shield were more often associated with buds, while specimens from erinea were variable. These results support the genetic evidence in that particular groups or morphotypes are not associated exclusively with specific plant niches. We propose that C. vitis is a complex of at least five genetically distinct but morphologically similar species, and that no one species can be assigned to a particular grapevine symptom.