The recent resurgence on water hyacinth in Lake Victoria has brought into the light the debate regarding the role of bio-control in the elimination of invasive species. Water hyacinth, a weed native to South America, caused significant damage to Lake Victoria through the late 1990’s followed by a decline in 1997. Several factors have been considered in determining the cause of this decline. In December of 1995, weevils were steadily released into Lake Victoria to reduce the massive mats of the weed that covered Lake Victoria (Williams et. al). During the 1997 decline in water hyacinth, an El Nino weather pattern occurred (Williams et. al.). Until the water hyacinth population began to regain lost ground in 2007 (NASA Earth Observatory 2007) bio-control methods, namely the weevils, were considered the explanation for water hyacinth population decline. The El Nino weather pattern was recently suggested as a significant contributing factor to previous water hyacinth decline (Williams et. al.). Arguments made in favor of each explanation must be critically evaluated as both presentations were published before the resurgence of water hyacinth was recorded.
Williams et. al. proposes that the El Nino weather pattern, not the weevil introduction, is responsible for the reduction in water hyacinth during 1997/1998. Wave action and reduced light levels, a result of the wet and cloudy weather, are suggested as facilitating weed decline (Williams et. al.) Wilson et. al. counters this argument suggesting that bio-control remains the primary explanation for weed decline. Instead of directly causing plant decline, the effects of El Nino only exacerbated the damage caused to the weevil-weakened water hyacinth population. Citing the basic tenant of bio-control, “it is sustainable through population regulation,” (Wilson et. al.) a convincing argument is made in favor of bio-control’s successful implementation in Lake Victoria.
Clearly, neither presentation can be considered conclusive as both were written prior to the 2007 water hyacinth resurgence. However, the evidence reviewed in both articles clearly indicates that bio-control is the main action responsible for water hyacinth decline. The El Nino weather pattern is demonstrated as exacerbating weed death; however, Williams et. al. fails to demonstrate El Nino as the sole cause of weed decline. Thus, I believe bio-control is the most suitable and successful method of water hyacinth control. A new strategy for eliminating new water hyacinth growth is imperative, but bio-control must be a component of this plan.
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. 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.