While differential thermal tolerances among interacting species have been documented in various systems (e.g. coral bleaching, ant microbiomes), the causes and consequences of this thermal mismatch have rarely been explored in complex multitrophic systems. Here we investigate the three-way interaction among an insect host (Manduca sexta), its insect parasitoid (Cotesia congregata), and the parasitoid endosymbiont (C. congregata bracovirus, CcBV). Recent studies found that the parasitoid has a lower thermal tolerance than its host; parasitized M. sexta tolerate heat-shock temperatures lethal to C. congregata. It is unclear whether parasitoid mortality is caused by heat directly (hypothesis 1), or by heat-induced disruption of host immunosuppression by CcBV, leading to parasitoid death via recovered host immune response (hypothesis 2). To test these hypotheses, we compared levels of immune response in parasitized and unparasitized M. sexta larvae under heat-shock and control temperatures. Preliminary results are consistent with hypothesis 2, indicated by a heightened immune response in the parasitized, heat-shocked group relative to the parasitized control group. This study contributes to the understanding of thermal mismatch, a critical step in predicting organismal and system-level responses to climate change.