n African Entomology - Impact of the weevils and (Coleoptera : Curculionidae) on water hyacinth, (Pontederiaceae), in Benin, West Africa




Between 1991 and 1993, two weevils species, (Warner) and Hustache (Col.: Curculionidae), were released at several localities on the Ouémé and Zou River systems in Benin for biological control of water hyacinth, . In Benin, became the dominant and ubiquitous species, whereas remained confined to the release localities. The impact of these weevils was assessed at two localities (Tévèdji and Lihu) between 1992 and 2000, by measuring water hyacinth cover, aspects of plant growth, and adult feeding damage. At both sites, water hyacinth cover was reduced from 100% to 5%. Leaf and petiole lengths were reduced by about 45% at Lihu and 60% at Tévèdji, indicating declining vigour of surviving plants. The number of adult feeding scars peaked 2-3 years after release of the weevils.


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