There is much debate as to the efficiency of bio-control on Lake Victoria. Weevils were first introduced as a method to control water hyacinth in 1995. During the first half of 1998 there was a sharp decline in the population, coinciding with El Nino; however, shortly after there was in increase. In early 1999 a steady decline began and continued. There is argument as to whether biological control was the major factor or if El Nino associated weather patterns were the primary cause behind the decline.
Wilson et al. (2007) take the stance that bio-control was the main factor behind the water hyacinth’s decline, although the stormy weather associated with El Nino also played a part. They argue that bio-control typically takes four years to take full affect and this situation stands true in Lake Victoria. They state that biological control agents were the only control measures in place and they cite similar cases where bio-control was effective. They also argue the effects of El Nino explain the seeming resurgence of water hyacinth in certain areas. They conclude by saying that although another resurgence of the plant is unlikely there must be continued monitoring of both water hyacinth and weevil populations.
Williams et al. (2007) state that, while weevils did have a role, the reduction of water hyacinth in the second quarter of 1998 was the result of El Nino. They claim that it was not only due to a reduced light climate, but also water level, wave action, and other weather-related factors. They conclude by saying that they agree that bio-control should continue to be a factor on Lake Victoria, but its limits need to be considered and monitored.
I do believe that bio-control of the water hyacinth has been effective and played a major role in the reduction of water hyacinth on Lake Victoria. However, I agree with Williams et al. (2007) that the decline in 1998 was due to El Nino, but after that time I think that it was the weevils taking effect. However, I think that due to the resurgence proved by the images from NASA Earth Observatory 2007) that the weevils have not been as effective as Wilson et al. seems to think. I think that bio-control is a good option and will continue to be effective, but it definitely has flaws and the situation in Lake Victoria must continue to be monitored.
NASA Earth Observatory. 2007 Water Hyacinth Re-Invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. 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. Aujuonu, 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