Management of water hyacinth (Eichhornia crassipes [Mart.] Solms) using bioagents in the Rift Valley of Ethiopia

This thesis presents a study on management of water hyacinth (<em>Eichhornia crassipes</em> [Mart.] Solms) using insects and fungal pathogens as bioagents. The main goal was to develop an effective biocontrol strategy for water hyacinth in the Rift Valley of Ethiopia. To this end, a field survey was conducted to assess the agro-ecological distribution of water hyacinth and of native fungal pathogens found in association with water hyacinth. We also performed laboratory and lath house experiments on (i) pathogenicity and host specificity of the fungal pathogens; (ii) adaptability, life table, efficacy and host specificity of the two <em>Neochetina </em>weevils; and (iii) the synergetic effects of integrated use of<em> Neochetina</em> weevils and fungal pathogen as bioagents. Survey results indicated that the weed is distributed in the Rift Valley water bodies located in low, mid and high altitude. The survey results also identified 25 fungal species found in association with water hyacinth that belonged to nine genera. Among the isolates, <em>Alternaria alternata</em>, <em>A. tenuissima</em>, and <em>Alternaria spp.</em> hold promise as possible bioagents of water hyacinth. Laboratory study on life cycle and development of <em>Neochetina</em> weevils indicated the two weevils took shorter generation time in Ethiopia than in Argentina but relatively similar to Kenya and Uganda. In Ethiopia, the two weevils produced four generations per year indicating their successful establishment. Feeding by adult weevils and tunneling by larvae significantly impacted the vigour and reproduction of water hyacinth plants. A herbivory loads of three pairs of <em>N. bruchi</em> and two pairs of <em>N. eichhorniae</em> showed the highest level of leaf damage and defoliated petioles. The study also reinforced that the two weevils are sufficiently host-specific. Finally, a study on integrated use of <em>Neochetina</em> weevils and an indigenous plant pathogen revealed that the two <em>Neochetina</em> weevils and the fungus <em>A. alternata</em> were together able to reduce the vegetative growth and fresh weight of water hyacinth plants considerably. This study recommends integrated use of fungal species and the two weevils to control water hyacinth. Implications of the findings are also discussed in the context of integrated water hyacinth management using the native fungal pathogens and the two weevils.