Effect of Silt Coverage of Water Hyacinth Roots on Pupation of Neochetina eichhorniae Warner and N. bruchi Hustache (Coleoptera: Curculionidae)

Observations under field conditions in Bangalore showed that release of Neochetina eichhorniae and N. bruchi (Coleoptera: Curculionidae) brought about successful control of the water hyacinth in water bodies where the plants were free-floating. However, in situations where the plants were partly anchored, suppression of the weed was achieved only 8 years after insect release. Studies carried out under glasshouse conditions, in which plants with free-floating and silt-covered roots were exposed to Neochetina spp., showed that fully grown larvae were incapable of pupating on silted roots of the water hyacinth. This resulted in reduced adult emergence of N. eichhorniae and N. bruchi, indicating that delayed suppression of water hyacinth in silted tanks may be due to the low population build-up of the weevils.