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Many parasites can interfere with their host’s defences tomaximize their fitness. Here, we investigated if there isheritable variation in the spider miteTetranychus evansifortraits associated with how they interact with their host plant.We also determined if this variation correlates with mitefecundity.Tetranychus evansican interfere with jasmonate (JA)defences which are the main determinant of anti-herbivoreimmunity in plants. We investigated (i) variation in fecundityin the presence and absence of JA defences, making use ofa wild-type tomato cultivar and a JA-deficient mutant(defenseless-1), and (ii) variation in the induction of JAdefences, in fourT. evansifield populations and 59 inbredlines created from an outbred population originating fromcontrolled crosses of the four field populations. We observed astrong positive genetic correlation between fecundity in thepresence (on wild-type) and the absence of JA defences (ondefenseless-1). However, fecundity did not correlate with themagnitude of induced JA defences in wild-type plants. Ourresults suggest that the performance of the specialistT. evansiis not related to their ability to manipulate plant defences,either because all lines can adequately reduce levels ofdefences, or because they are resistant to them.

Many parasites can interfere with their host's defences to maximize their fitness. Here, we investigated if there is a heritable variation in the spider mite, Tetranychus evansi for traits associated with how they interact with their host plant. We also determined if this variation correlates with mite fecundity. Tetranychus evansi can interfere with jasmonate (JA) defences which are the main determinant of anti-herbivore immunity in plants. We investigated (i) variation in fecundity in the presence and absence of JA defences, making use of a wild-type tomato cultivar and a JA-deficient mutant (defenseless-1), and (ii) variation in the induction of JA defences, in four T. evansi field populations and 59 inbred lines created from an outbred population originating from controlled crosses of the four-field populations. We observed a strong positive genetic correlation between fecundity in the presence (on WT) and the absence of JA defences (on def-1). However, fecundity did not correlate with the magnitude of induced JA defences in WT plants. Our results suggest that the performance of the specialist T. evansi is not related to their ability to manipulate plant defences, either because all lines can adequately reduce levels of defences, or because they are resistant to them.