Many parasites can interfere with their host's defences to maximize their fitness. Here, we investigated if there is heritable variation in the spider miteTetranychus evansifor traits associated with how they interact with their host plant. We also determined if this variation correlates with mite fecundity.Tetranychus evansican 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 fourT. evansifield 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 wild-type) and the absence of JA defences (ondefenseless-1). However, fecundity did not correlate with the magnitude of induced JA defences in wild-type plants. Our results 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 of defences, or because they are resistant to them.