Mites as vector of Tulip Virus X in stored tulip bulbs

Tulip virus X (TVX) is a Potexvirus causing economic losses in tulip. Potexviruses are generally transmitted by mechanical contact and, indeed, several mechanical transmission pathways for TVX have been identified during tulip bulb production. However, TVX transmission does also seem to occur during bulb storage. Since mechanical transmission is excluded in this period, a biological vector should be involved. The eriophyoid mite Aceria tulipae, the acarid storage mite Tyrophagus putrescentiae, and the acarid bulb mite Rhizoglyphus echinopus are the main arthropod pests of stored tulip bulbs. Therefore, we studied their putative role in transmission of TVX during tulip bulb storage. We show that mites of each of these species can carry TVX with them after feeding on TVX-infected bulbs. In addition, some of the healthy bulbs acquired an infection with TVX when inoculated with mites. Although the current setup of the experiments does not confirm which species of mite transmit TVX, we have strong indications that mites are involved in transmission. Additional research with larger numbers of independent replicates is required to further prove the vector status of each species of mite, the efficiency, and mode of virus transmission. If our results will be confirmed, this would be the first case reporting a Potexvirus to be transmitted by mites, and the first case of an association between acarid mites and a plant pathogenic virus. Consequently, TVX control in tulip bulb production should include an adequate control strategy of both eriophyoid and acarid mites.