A QTL associated with leaf trichome traits has a major influence on the abundance of the predatory mite in a hybrid grapevine population.

The abundance of predatory phytoseiid mites, , important biological control agents of spider mite pests in numerous crops, is positively influenced by the density of leaf trichomes and tuft-form domatia in vein axils. Identification of the genetic regions controlling both trophic levels could facilitate the improvement of predatory mite habitat in breeding programs. The abundance of and non-glandular trichomes was measured in a segregating F family derived from the cross of the complex hybrid, 'Horizon', with Illinois 547-1 ( B38 ×  B9), finding positive correlation among traits. High density genetic maps were used to localize one major quantitative trait locus (QTL) on chromosome 1 of Illinois 547-1 associated with both predatory mite abundance and leaf trichomes. This QTL explained 23% of the variation in phytoseiid abundance and similar amounts of variance in domatia rating (21%), domatia size (16%), leaf bristle density (37% in veins and 33% in blades), and leaf hair density (20% in veins and 15% in blades). Another nine QTL distributed among chromosomes 1, 2, 5, 8, and 15 were associated solely with trichome density, and explained 7-17% of the phenotypic variation. Combined, our results provide evidence of the genetic architecture of non-glandular trichomes in , with a major locus influencing trichome densities, domatia size and predatory mite abundance. This information is relevant for breeding grapevines with a more favorable habitat for biological control agents.