Highlights ► We tested effects of Ormia ochracea larval infestation on the singing activity, songs and mass of Gryllus lineaticeps. ► Infested males were significantly less likely to sing than noninfested males, but did not differ in their songs. ► Infested males gained significantly more mass than noninfested males. ► Parasitoid larvae that developed in males that gained more mass were heavier as pupae. ► Changes in host traits seem to benefit the parasitoid, but they may also be side-effects of a general immune response.