Dryophthorinae includes some of the most economically important weevil pests. Feeding damage on host plant occurs primarily during the endophytic larval stages. The immature stages of only approximately 5% of dryophthorine genera are currently known. Traditional Ecological Knowledge of the Dawu People of the island of Lanyu led to the discovery of the immature stages and host plant of the dryophthorine weevil genus Poteriophorus Schoenherr. The larva, pupa, and biology of Poteriophorus uhlemanni (Schultze, 1922) are described for the first time. The newly discovered larva is compared to closely related taxa, including two of the most economically important and commonly encountered genera in Sphenophorina: Metamasius Horn, 1873 and Sphenophorus Schoenherr, 1838. Discovery of the associated larval and pupal stages of P. uhlemanni provides suites of characters for morphologically based phylogenetic studies, insights into the larva's functional morphology of feeding, tunneling, and cocoon-making behavior, and the ability to accurately identify the species at all stages.Knowledge of host preference will inform management strategies for poorly studied endemic species in the area.