In recent years, bio-control has become a popular but controversial subject in environmental science fields. Many times, it has not worked out the way scientists predicted and has actually had negative impacts on the very ecosystems that they were trying to help. People first reported water hyacinths on Lake Victoria in 1989. Since then, they have spread exponentially covering tens of thousands of hectares of water surface hampering transportation, fishing, and the lake’s biodiversity.
Wilson et al. explain that in 1995, scientists imported bio-control agents called weevils into the Great Lakes Region to control water hyacinth growth. They continue to discuss that in 1997/1998, there was an El Nino weather pattern in the region, which caused very stormy and wet weather. Wilson et al. believe that the reduction in water hyacinth occurred as a result of the weevils and that there is little chance of a resurgence of water hyacinth. They argue that water hyacinth continued to grow until 1998 then had a small reduction coinciding with the El Nino and then continued to multiply further until 2000. Then, at that point, there was a significant reduction of water hyacinth; they state that this timeline of approximately four years before weevils were effective is similar to that of other bio-control situations elsewhere (2007).
Williams et al. have different ideas; they do not deny that the bio-control helped control water hyacinth growth. However, they maintain that the El Nino greatly accelerated this process by the wet weather and wave action. They state that there was a small growth of water hyacinth in 2000-2001 and believe that it is very likely to see a resurgence soon because weevils were not solely responsible for the decrease in water hyacinth. Furthermore, many weevils were destroyed in the El Nino weather as well (2007).
I believe that both sides present excellent evidence supporting their arguments; however, due to Wilson et al.’s explanation of the typical timeline of biodiversity, I am inclined to believe that they are more convincing than Williams et al. Nevertheless, the recent NASA satellite images clearly depict that the weevils did not have as significant an impact as Williams et al. thought or were unable to perform their intended purpose after El Nino. I think this situation illustrates that bio-control can be helpful, but one must be prepared when implementing this strategy for unexpected results or complications.
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.