Invasive plant species can cause drastic changes to ecosystems by displacing native plant and animal species. In aquatic environments, invasive plants can clog waterways and be especially difficult to control. One success story is the control of Alligator Weed, Alternanthera philoxeroides.
Alligator Weed was introduced to the US in 1897 near Mobile, Alabama. The Alligator Weed is salt tolerant, shades native aquatic plants and reduces the oxygen level of the water. Open water habitat is filled by Alligator Weed displacing native plants, fish and other animals. By 1963, Alligator Weed covered over 250 square miles of waterway in 8 southern US states.
Search for potential control agents identified a Brazilian flea beetle, Agasicles hygrophila. Agasicles hygrophila has a single host plant, Alligator Weed. A single host plant is desirable because the agent is less likely to feed on and adversely affect native plant species. Agasicles hygrophila was released in the US in 1963. Twenty years after Agasicles hygrophila was introduced to the US, the Alligator Weed population was reduced by 99 percent. Today, Alligator Weed is no longer a major problem in most US waterways. The Alligator Weed is kept in check by Agasicles hygrophila
Agasicles hygrophila is the oldest example of using insects as biocontrol agents for invasive weeds. It is fortunate that this insect can consume enough of the invasive weed to control it and not cause damage to any native plants. Most invasive species problems do not have such elegant solutions.