Down-regulation of plant defence in a resident spider mite species and its effect upon con- and heterospecifics
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Herbivorous spider mites occurring on tomato plants (Solanum lycopersicum L.) cope with plant defences in various manners: the invasive Tetranychus evansi reduces defences below constitutive levels, whereas several strains of T. urticae induce such defences and others suppress them. In the Mediterranean region, these two species co-occur on tomato plants with T. ludeni, another closely related spider mite species. Unravelling how this third mite species affects plant defences is thus fundamental to understanding the outcome of herbivore interactions in this system. To test the effect of T. ludeni on tomato plant defences, we measured (1) the activity of proteinase inhibitors, indicating the induction of plant defences, in those plants, and (2) mite performance on plants previously infested with each mite species. We show that the performance of T. evansi and T. ludeni on plants previously infested with T. ludeni or T. evansi was better than on clean plants, indicating that these two mite species down-regulate plant defences. We also show that plants attacked by these mite species had lower activity of proteinase inhibitors than clean plants, whereas herbivory by T. urticae increased the activity of these proteins and resulted in reduced spider mite performance. This study thus shows that the property of down-regulation of plant defences below constitutive levels also occurs in T. ludeni.
KeywordsTetranychus ludeni Spider mites Plant defences Proteinase inhibitors Plant–herbivore interactions
We thank Felipe Lemos for sending mite strains from Amsterdam, Flore Zélé for all the improvements of the greenhouse facilities, and genetic identification of spider mites, Inês Santos for taking care of plants and mite populations and the whole mite squad (FZ, IS, Leonor Rodrigues, Ana Rita Ponce, Gonçalo Matos and Salomé Clemente) for stimulating discussions. DG thanks Cristina Branquinho for logistic support. This work was funded by an FCT-ANR project (FCT-ANR//BIA-EVF/0013/2012) to SM and Isabelle Olivieri. TM acknowledges a Post Doc grant SFRH/BPD/85419/2012.
Author contribution statement
DG, SM and AJ conceived and designed the experiments. DG performed the experiments, with help from TD and CC in the proteinase activity analysis. DG and SM analyzed the data and wrote the manuscript, with considerable contributions from AJ.
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