Tetranychus evansi spider mite populations suppress tomato defences to varying degrees

Plant defence suppression is an offensive strategy of herbivores, in which they manipulate plant physiological processes to increase their performance. Paradoxically, defence suppression does not always benefit the defence-suppressing herbivores, because lowered plant defences can also enhance the performance of competing herbivores and can expose herbivores to increased predation. Suppression of plant defence may therefore entail considerable ecological costs depending on the presence of competitors and natural enemies in a community. Hence, we hypothesize that the optimal magnitude of suppression differs among locations. To investigate this, we studied defence suppression across populations of Tetranychus evansi spider mites, a herbivore from South America that is an invasive pest of solanaceous plants including cultivated tomato, Solanum lycopersicum, in other parts of the world. We measured the level of expression of defence marker genes in tomato plants after infestation with mites...