There’s something about Weevil
Since its introduction in the late twentieth century, water hyacinth has been a major nuisance in Lake Victoria. Not only does it pollute the water by disrupting the lake’s flow, but because of the plant’s massive undergrowth, also reduces fishermen’s abilities to make a living and poses as a major threat to native species. To attempt to counteract this invasive species, in 1995, weevils, which are small herbivore beetles and natural predators of water hyacinth, were released into the water hyacinth clusters as biological control agents.
However, according to Williams et al. (2006), though the weevils aided in the reduction of water hyacinth in Lake Victoria from 1999 to 2000, they were not the main reason for the plant’s reduction. Another factor, the El Nino of 1997 – 1998, which had been the biggest ever recorded in the twentieth century, was, according to Williams et al. (2006), the most important contributing factor to the water hyacinth’s decline. Williams et al. (2006) argues that it was because of a combination of timing, reduced sunlight, and weevils, that the decline of water hyacinth in 1999/2000 was so dramatic. Therefore, Williams et al. (2006) warns that now the El Nino has calmed, the water hyacinth will resurge; the weevils will be unable to keep the plant population under control.
Wilson et al. (2006), on the other hand, argues that the weevils were crucial, if not the only factor in the water hyacinth’s decline, and that the El Nino had little effect on the plant’s growth. This is because, according to Wilson et al. (2006), the weevils generally takes three to five years to fully reach their potential and the decline in water hyacinth fits that timeline perfectly in accordance with the three releases of weevil nests into the water hyacinth clusters. The El Nino, on the other hand, though would have moved already weevil-weakened water hyacinth mats around, could not have had reduced water hyacinth growth by increased cloud cover; there is no substantive link between low light and water hyacinth concentration. (Wilson et al., 2006)
In light of all the evidence, I think that Williams et al. (2006) gives a more convincing argument than Wilson et al. (2006), because the latter neglected many sides of the former’s argument, and did not even consider the possibility that water hyacinth might return, even if it weren’t because of the El Nino’s dispersion.
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 2010.
Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.
Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.