Zeugodacus tau Walker (Diptera: Tephritidae) is a quarantine pest of cucurbit crops in China. In recent years, the damage it has caused to Trichosanthes kirilowii (Cucurbitales: Cucurbitaceae) has increased, but evidence for host adaptation and population growth on this plant remains limited. We investigated the suitability of T. kirilowii as a host plant for Z. tau, compared with the known suitable host Cucurbita moschata, by examining adult olfactory preference, oviposition choice, and demographic performance using an age–stage, two-sex life table. Females preferred T. kirilowii significantly more than C. moschata in cases of both peeled and unpeeled fruits, whereas males showed no significant difference. Oviposition was also higher on T. kirilowii and further increased on peeled fruit. Developmental duration, total longevity, ovipositing days, oviposition period, and hatching rate did not differ between the two host species. However, Z. tau reared on T. kirilowii exhibited significantly shorter APOP and TPOP, along with higher fecundity and increased pupal weight. Life table parameters indicated higher intrinsic (r = 0.1028 ± 0.0040 d⁻¹) and finite rates of increase (λ = 1.1083 ± 0.0044 d⁻¹) on T. kirilowii, whereas R₀ was similar and mean generation time was shortened by 11.61 d. A 100-day projection predicted 11,980 adults from T. kirilowii compared to 1231 from C. moschata. Overall, T. kirilowii is a highly suitable host that supports the rapid population growth of Z. tau.