Distorted tomato trichomes facilitate biological control of the tomato russet mite using predatory mites

Abstract: The tomato russet mite (Aculops lycopersici) is an eriophyid mite that is distributedworldwide and can cause major economic losses on tomato crops. Adult mites are 150 micronslong and due to this small size they are only detected in the crop once the population is alreadytoo large to prevent damage to the plants. Currently, the control of this pest is based on acaricidetreatments (e. g. Sulfur) since there is no effective biological control agent available yet. Animportant reason for ineffective biological control is the presence of trichomes on tomato – i.e. epidermal hairs that produce and store multitudes of secondary metabolites. These structuresphysically protect the russet mite against natural enemies while impeding and/or intoxicatingsmall biological control agents. This also applies to predacious phytoseiid mites. To tackle theseissues and to facilitate biocontrol we have selected a tomato genotype with a mutation in thehairless locus – and therefore possess distorted trichomes – to test the effect of this phenotypeon russet mite performance in absence/presence of predatory mites in laboratory andgreenhouse conditions. Contrary to our expectations the population growth of the herbivore wassignificantly delayed on the hair mutant compared to the wild type with the normal trichomerepertoire. In addition, the population of the predatory mite Amblydromalus limonicus reachedhigher densities on the infested hairless genotype and, consequently, suppressed the pest wellon these plants. Overall, we show that removal of a classical resistance trait, rather thanintroducing it, may result in better direct and indirect protection against devastating herbivores.