The Effect of Water Nutrients on the Feeding Intensity and Development of Larvae ofNeochetina eichhorniae(Warner) (Coleoptera: Curculionidae), a Biocontrol Agent of the Invasive Water Hyacinth

Abstract

Water hyacinth is one of the five worst aquatic weeds that invades many SouthAfrican water bodies. It has been the target of at least eight biological control agents, including the water hyacinth weevil, Neochetina eichhorniae (Warner) (Coleoptera: Curculionidae). However, their success has been constrained by the high levels of eutrophication in South African water bodies, which promotes the plant's rapid compensation for feeding damage and growth. The aim of this research was to investigate the influence of water nutrients on the feeding and development of N. eichhorniae larvae.Water hyacinth plants were maintained at three different nutrient concentrations high (6 mg/l N; 0.83 mg/l P), medium (2.5 mg/l N; 0.4 mg/l P) and low (0.7 mg/l N; 0.01 mg/l P). The plants in each of these treatments were then inoculated with two larvae per plant, while the controls were kept free of larvae. Plant biomass and the number of leaves per plant were measured weekly for eight weeks. The results showed an increase in larval feeding rate as nutrient levels decreased. In contrast, larger larval size, greater numbers of survivors and shorter larval developmental time were recorded as nutrient concentrations increased from low to high levels. The findings of this study will therefore be helpful to understand how larval damage by N. eichhorniae affects water hyacinth populations and to predict the success of biocontrol under different nutrient levels.