Occurrence of herbivore arthropods on water hyacinth in the Central Rift Valley of Ethiopia

Water hyacinth [Pontederiaceae: Pontederia(= Eichhornia) crassipes Mart.] is an invasive alien aquatic weed distributed worldwide on freshwater bodies. More than one hundred species of arthropods have been found to feed on water hyacinth. Still, only a few are used as traditional biological control agents. The weed invaded freshwater bodies, but officially no biological control agents were implemented to manage it in Ethiopia. This study determined the occurrence of the water hyacinth-associated herbivore arthropods and their impact on the weed in the country. Randomly selected 0.5 m² quadrats containing damaged water hyacinth plants were collected seasonally from Lake Koka, Lake Ziway, and Wonji Sugar Cane Farm drain. The weed growth parameters, herbivore species, and density were determined. Neochetina bruchi and Neochetina eichhorniae, Spodoptera littoralis, Aphis gossypii, and Tetranychus urticae were the identified herbivores. Statistical analysis was carried out using SAS version 9.4. Higher number of N. bruchi (8.6/quadrat), and N. eichhorniae (1.2/quadrat) were found in the wet season on Lake Koka. Higher densities of S. littoralis (6.9/quadrat), A. gossypii (21.8/plant), and T. urticae (5.8/plant) were in the dry season at Wonji drain. In the growth parameters of the water hyacinth, higher weed number (249.4/quadrat), weight (29.0 kg/quadrat), and infestation percentage (17.8/quadrat) were found in the wet season at the Wonji drain. The density of the Neochetina spp. recorded per water hyacinth plant was inadequate to manage it without augmentation. Moreover, there should be further investigation to determine the effects of indigenous herbivores on the water hyacinth.