Technical Abstract: Thripinema fuscum is a natural enemy capable of reducing local populations of Frankliniella fusca and reducing transmission of plant diseases vectored by F. fusca. We used light and electron microscopy to detail the in vivo life cycle of the nematode and to determine the effects of parasitism on thrips host tissues. The parasitic T. fuscum female underwent numerous morphological changes upon ingress into the host hoemocoel. She produced eggs within four to five days after ingress and the host hemocoel became packed with eggs and developing juvenile nematodes. Mature juveniles migrated to the hindgut and fully developed juveniles first emerged from the posterior end of the male or female F. fusca nine days post-parasitization. Parasitization induced a displacement of the host alimentary tract, an atrophy of the ovaries and fat body, and an alteration of energy and waste reserves in host tissues. Our observations reveal a specialized relationship showing that this parasite is well adapted to exploit host digestive, reproductive, and excretory systems. This study is a step towards understanding how histopathological alterations induced by T. fuscum influence the ability of F. fusca to transmit disease.