Field observations suggested that the introduced Hydrilla verticillata (L.f.) Royle biological control agent, a stem weevil, Bagous hydrillae O’Brien, would feed on hydrilla tubers and stems, and a native species, Bagous restrictus LeConte, would feed on hydrilla stems. In choice tests, B. hydrillae readily oviposited in hydrilla tubers. Larval development of B. hydrillae in hydrilla tubers was similar to that in stems; greater adult biomass was attained and less time was needed to complete development when the larvae were fed tubers. Larvae of the hydrilla tuber weevil, B. affinis Hustache, did not complete development in hydrilla stems. Larvae of B. affinis completed development more rapidly when fed new compared with old hydrilla tubers. The native B. restrictus successfully completed development in hydrilla stems, although the larvae required slightly more time compared with the biocontrol agent, B. hydrillae. These findings indicated that feeding on tubers by B. hydrillae may benefit the species particularly when hydrilla stems are seasonably absent or unsuitable especially in more northern climates. In terms of hydrilla control, damage to tubers by this species constitutes a reduction in future infestations of hydrilla propagated by tubers. Finally, hydrilla is suitable to the native weevil, B. restrictus, because larvae completed development in hydrilla stems.
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