FEEDING BY BAGOUS-AFFINIS (COLEOPTERA, CURCULIONIDAE) INHIBITS GERMINATION OF HYDRILLA TUBERS

Bagous affinis Hustache (Coleoptera: Curculionidae) larvae feed inside subterranean turions or tubers of hydrilla (Hydrilla verticillata (L.f) Royle, Hydrocharitaceae) during low water conditions. This results in reduced germination of the tubers. To determine the number of B. affinis required to reduce tuber germination, dioecious hydrilla tubers were exposed to various B. affinis egg to tuber ratios. The tubers were then held for germination. The number of adults produced and the number of tubers germinating for each treatment and damage category were recorded. In all treatments, tuber germination was significantly reduced compared with the controls. The proportion of tubers germinating tended to decrease with an increase in the number of eggs initially placed in the treatment. This reduction in germination resulted from an increase in feeding damage. The results of this study suggest that B. affinis should be released in the field with an egg to tuber ratio of 2:1 or greater.