The Effects of Herbivory by a Weevil Species, Acting Alone and Unrestrained by Natural Enemies, on Growth and Phenology of the Weed Sesbania punicea

Abstract

SUMMARY (1) An apionid weevil, Trichapion lativentre (Beguin-Billecocq), has been introduced into South Africa where it is the only herbivore of any consequence on the South American legume Sesbania punicea (Cav.) Benth. Its impact on plant performance is not restrained by any competitors or natural enemies. (2) Plant growth at weevil-free sites was compared to that at sites colonized by the weevils for one and for two seasons. Relative growth curves are used to describe the effects of weevil feeding on above-ground productivity and phenology of the host-plant. (3) Feeding by the adult weevils suppressed leaf-set, caused premature abscission of the leaflets, and reduced stem growth. Larval feeding destroyed most of the buds and greatly reduced flowering and seed production. The mean mass of individual seeds increased as a consequence of weevil herbivory. (4) These effects on vegetative and reproductive growth were exacerbated at sites that had been colonized by weevils for two seasons. (5) It has yet to be established whether the impact of herbivory by T. lativentre will reduce the density and spread of S. punicea and result in successful biological control of the weed.