Abstract:
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.