An Environmentally-Friendly and Participatory Approach to the Management of an Invasive Aquatic Weed

2010

English

Biological control of water fern, Salvinia molesta was studied in concrete tanks of area 4 m2 each at the insectary of the Department of Animal Biology and Conservation Science (DABCS), University of Ghana, Legon and Jewi Wharf in the Western Region. The impact of Cyrtobagous salviniae on S. molesta was studied in Legon and Jewi Wharf. Results show that there was damage inflicted on S. molesta by the C. salviniae which manifested with increase in percentage and area damage of S. molesta with time in both locations (correlation coefficient = 0.99 in both cases). The damage became evident when leaves turned brown due to infestation, with the leaves being more likely to fall off during handling The rate of multiplication of C. salviniae was also studied through the numbers recovered per quadrat Population estimation using a 0.25 m * 0.25 m quadrat during sampling yielded up to 525 adult weevils in the tank at Legon in two months, giving a 6.4 fold increase in population and a density of 131 adult weevils per square metre, that of Jewi Wharf yielded 608 adult weevils in the tank by the third month giving a 16.4 fold increase in population and a density of 152 adult weevils per square metre. The results indicated that C. salviniae was able to survive and reproduce on S. molesta. The results also indicated that S. molesta reduced in area coverage due to damage and the population of C. salviniae also reduced in a predator-prey relationship pattern. Assessment of biological control potential of a closely related species, Salvinia nymphellula in a large plastic pool at DABCS and on the lower Volta (Big Ada) in the Greater Accra Region was also carried out. The impact of C. salviniae released was monitored over a five month period in Legon and in the lower Volta. Sampling was done to determine the percentage damage of S. nymphellula by C. salviniae. The results indicated that C. salviniae could not survive and reproduce on S. nymphellula. As a result, there was no damage characterized by C. salviniae. The results confirm the fact that C. salviniae is host-specific to S. molesta and will not even feed on a closely related species, 5. nymphellula. The results of the community perceptions on invasive weeds and their control indicated that the communities prefer manual control of weeds to any other method. The Jewi Wharf community was aware of biological control of weeds but not that of the lower Volta. Jewi Wharf community however had mixed perceptions of biological control and did not prefer the method. It was again indicated that perceptions on the invasive water weeds were based on the socioeconomic effects which they encounter from the spread of the weeds, as it has always been the case in other parts of the world where the weeds are prevalent.

Awuni, S.