Controlling <i>Scaphoideus titanus</i>: are pyrethrins and phytoseids compatible?

Mites of the family Phytoseiidae are important generalist predators in European vineyards, where they regulate phytophagous tetranychid and eriophyoid mites. As long as they are not affected by pesticides, they survive, even without prey. Although most fungicides are of low toxicity to Phytoseiidae, some insecticides, notably pyrethroids and pyrethrins, can impact their populations. Today, the application of insecticides within vineyards is reduced thanks to the use of methods such as mating disruption against grapevine moths. However, their use is mandatory in some European and Swiss regions to control the leafhopper Scaphoideus titanus to prevent the transmission of Flavescence dorée, a quarantine phytoplasma-born disease. Currently, pyrethrins are the only registered insecticides for managing S. titanus in Swiss vineyards. Despite their toxicity to phytoseid mites, their low persistence usually allows for a quick recolonisation of treated vineyards by these predatory mites. However, due to the recent reports of winegrowers, this assumption has come under scrutiny of an increase in spring grape rust mite damage by the eriophyoid mite Calepitrimerus vitis in mandatory control areas. To verify the impact of pyrethrins on predatory mites, we monitored 70 Chasselas plots in western Switzerland to compare densities of phytoseids as well as tetranychids and estimated eriophyoid mites’ damages in vineyards treated with pyrethrins the previous year with those in untreated plots. Data collected in spring 2023 and 2024 emphasised no significant differences in Phytoseiidae densities between insecticide-treated and untreated plots. Phytoseid species appeared to be randomly distributed between pyrethrin-treated and untreated plots, with Typhlodromus pyri being the dominant species. Moreover, the densities of phytophagous mites and grape rust mite damage were low and did not differ between the two treatments. We therefore observed no indications that the application of pyrethrins for the management of Flavescence dorée harms predator mite populations or that these beneficial agents no longer regulate phytophagous mites.