One of the most troublesome exotic weeds as I have mentioned above is the Water Hyacinth. The Mottled Water Hyacinth weevil (Neochetina eichhorniae), has proven to be most effective in killing the plants. A typical water hyacinth plant can produce in a single season produce as many as 65,000 plants. Mechanical removal works only in limited areas. There are not enough grass carp or manatees to manage removal of all the plants in all areas. Thus another biological control factor is the use of the weevil.
The weevil is able to complete a cycle from eggs to adults, in three months. The female deposits her eggs in the tissue of a leaf or in the upper petiole (leaf stalk), of the hyacinth plants. In seven to ten days the larvae (grubs) hatch out and they then tunnel thoughout the interior of the plant, eating the vital crown areas and leaving brown streaks of dead or dying plant tissue to mark where they have been.
After spending time chewing there way throughout the plant, the larvae exist the plant under water and attach themselves to the extenive root systems of the hyacinth. The larvae weevil forms a cocoon, and within a couple of weeks the adult weevil emerges. The adults are nocturnal, meaning they only feed at night on the outer surface of the plants. The presence of these adult weevils is show on the plants by a polka dot pattern of small brown spots, which are dead plant cells that surround the area where the weevils have eaten. Their eating pattern allows the spread of fungus infections in the plants as well, thus since their release in 1972, they have proven to be a perfect natural control in Florida waters.
