The host plant range of two ricefield caseworms, Parapoynx fluctuosalis (Zeller) and P. diminutalis Snellen (Lepidoptera: Pyralidae), was determined from screening rice and 61 weeds in the Philippines. Both species developed best on the aquatic weed Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae). Parapoynx fluctuosalis also completed a full generation from egg to egg on Cyperus brevifolius (Rottb.) Hassk. (Cyperaceae), Commelina diffusa Burm. f. (Commelinaceae), Leptochloa chinensis (L.) Nees, and Paspalum conjugatum Berg (Poaceae). Parapoynx diminutalis completed a generation on Chara vulgaris L. (Characeae), Ottelia alismoides (L.) Vahl and Blyxa auberti Rich. (Hydrocharitaceae), and Cyperus rotundus L. (Cyperaceae).