Effects of water hyacinth Eichhornia crassipes root extracts on midge Chironomus ramosus larvae: a preliminary note

The effects of crude root extracts of Eichhornia crassipes (Marts) Solms on Chironomus ramosus Chaudhuri eggs and larvae are studied under laboratory conditions. Egg masses of C. ramosus that are subjected to varying concentrations of exudates (final concentrations 0.25-2.5%) show 100% viability. However, larvae reared further at these concentrations reveal a dose-response relationship, with an LC50 value of 1.33% and an LC90 value of 2.05%. A striking feature is the occurrence of supernumerary salivary glands in larvae (three glands per larva) reared in the 1%, 1.25%, 1.5% and 1.75% extracts. This deviates from the normal two glands per larva and may be explained by altered growth as a result of the putative bioactive compounds present in the hyacinth extracts. In nature, hyacinth and midges co-exist in many freshwater habitats, implying that hyacinth compounds present from natural leaching could be encountered by the larvae. These preliminary findings suggest that hyacinth can influence the larval development of midges, giving rise to long-term ecological implications.