The Decline of Water Hyacinth on Lake Victoria
Scientific groups have recently debated the causes and factors behind water hyacinth decline on Lake Victoria. Evidence strongly supports the theory of biological control, South American weevils, as the primary reason for decline. However, scientists also argue that the El Nino weather patterns that occurred during the latter half of 1997 and the first half of 1998 have played a major role in destroying water hyacinth populations. Wilson et al. (2007) concludes that while the stormy weather and increased waves/currents on Lake Victoria associated with El Nino have contributed to vast damage of water hyacinth on Lake Victoria, foreign South American weevils were the ultimate factor in controlling this invasive species. However, on the other hand, Williams et al. (2005) asserts that although biological control played a large role in reducing water hyacinth populations, El Nino weather patterns deserve the most recognition for widespread population control. Thus, both articles and parties disagree on one main point: the degree of importance of each contributing factors.
Wilson et al. (2007) describes in depth the processes of using Neochetina weevils as biological control agents. Neochetina larvae tunnel into the water hyacinth through the root-stock and petioles. This allowed bacteria and fungi to infect the plant and cause massive damage. Flooding of larval tunnels and weakened tissue water-log, sink, and ultimately kill the water hyacinth mats. The increased wind and wave action due to El Nino further supported the destruction already attributed to the South American weevils. Therefore, the author stresses that without biological control agents, the huge problems associated with this invasive species would not have been resolved.
Williams et al. (2005) emphasizes that plant quality affects the efficiency of weevils. Plant deterioration and leaf damage kills eggs and young larvae, causing deterioration in weevil populations as well. Furthermore, the water hyacinth decline mimicked the widespread vegetation destruction caused by El Nino throughout eastern Africa. Thus, the power of nature trumped human intervention via biological control.
Perhaps the definitive answer to this debate will lie in the following solution: if authorities continue investing in the weevil populations and the water hyacinth population returns, Williams et al. (2005) will emerge as victor.