Based on this PRA, Tetranychus mexicanus was added to the EPPO Lists of pests recommended for regulation as quarantine pests in 2023. Measures are recommended for host plants for planting with leaves

Main conclusions: 

Entry. The likelihood of entry on host plants for planting with leaves was considered as high, with a moderate uncertainty. On other pathways studied (host plants for planting without leaves, cut fresh plant parts of hosts and host fruit), the likelihood of entry was rated as low or very low, with moderate uncertainty. 

Establishment. The environmental requirements of T. mexicanus defined the area of establishment (described above), in which the likelihood of establishment outdoors is very high with a low uncertainty. Protected conditions are generally suitable to the pest. In areas where it can establish outdoors, the likelihood of establishment under protected conditions is as for establishment outdoors. In areas where T. mexicanus cannot establish outdoors, the likelihood of establishment is assessed to be moderate (with a moderate uncertainty) in greenhouses where host plants are present year-round. In greenhouses or greenhouse areas where host plants are only present part of the year, establishment is unlikely. 

The magnitude of spread was considered moderate with a moderate uncertainty, mainly based on the spread of the invasive (sub)tropical species Tetranychus evansi in the Mediterranean area. Tetranychus mexicanus could spread locally by natural dispersal, and at long distance through human-assisted pathways.

Impact in the current distribution of the mite was rated as low overall, with a moderate uncertainty. Evidence of impact is mostly available from Brazil, where T. mexicanus is generally considered a secondary pest that only causes economic damage in some crops and only under favourable conditions. In the EPPO region, the potential impact was also rated as low. However, there is a high uncertainty linked to the differences between the EPPO region and the current area of distribution of T. mexicanus, in relation to cultivated host plants, cropping practices and environmental conditions. In particular, at least in the EU, the number of registered pesticides may decrease in the future. In addition, the efficacy of natural enemies and commercially available biological control agents that are present in the EPPO region against T. mexicanus is not known. Further, the pest may attack plant species in the EPPO region that are currently not damaged by other spider mites and the introduction of T. mexicanus on these plants lead to an increased impact by spider mites. The Panel on Phytosanitary Measures further noted that the major uncertainty relating to potential impact is how the pest will affect varieties of orange, as well as other species of Citrus and ornamental species, that are grown in the EPPO region. If those varieties and species prove to be susceptible to the pest, the overall potential impact may be higher. 

Phytosanitary measures to reduce the probability of entry: The EWG identified phytosanitary measures for host plants for planting with leaves (except tissue cultures) (details in section 16 and Annex 1).