Technical Abstract: • The gene-for-gene interaction triggering resistance of wheat against the Hessian fly utilizes specialized defense response genes not previously identified in other interactions with pests or pathogens. • The expression of Hfr-3, a gene encoding a novel wheat germ agglutinin-like protein, was characterized by sequencing, qRT-PCR, western blots and genetic mapping. • Quantification of Hfr-3 mRNA in the incompatible interaction confirmed a rapid response up to 3000-fold above the uninfested control. mRNA abundance was influenced by the number of larvae per plant, suggesting localized rather than systemic resistance. Hfr-3 was also responsive to bird cherry-oat aphid, but not to other biotic and abiotic factors tested. Within each of four chitin-binding domains, the predicted protein contained five conserved saccharide-binding residues. HFR-3 protein increased in parallel to the mRNA during incompatible interactions and was detected in both virulent and avirulent larvae, indicating ingestion. • Antinutritional proteins, such as lectins, may be responsible for the apparent death by starvation of avirulent Hessian fly larvae during the initial few days of incompatible interactions with resistant wheat plants.