Aquatic Plant Control Research Program. Biological Control of Pistia stratiotes L. (Waterlettuce) Using Neohydronomus affinis Hustache (Coleoptera: Curculionidae).
FORT LAUDERDALE RESEARCH AND EDUCATION CENTER FL
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Waterlettuce Pistia stratiotes L. is a floating plant that often interferes with the proper use of water resources. Consequently, releases of a biological control agent, Neohydronomus affinis Hustache a weevil, were begun in April 1987 at several sites in southern Florida. Self-perpetuating populations had established at four of these sites by September 1988. The plant and weevil populations were monitored on a monthly basis at three sites Kreamer Island, Torry Island, and Port St. Lucie. By May 1989, Kreamer Island harbored about 45 million weevils, and the plant population had been reduced from 50 acres 202,343 sq m to less than 5 acres 20,234 sq m. By May 1990, Torry Island harbored nearly 42 million weevils and P. stratiotes, which had previously filled the 10-acre 40,468 sq m site, was virtually absent. The biocontrol agent population at Port St. Lucie never exceeded 100,000 weevils and had little apparent impact on the waterlettuce population at this site. Plants under stress from weevil herbivory at Kreamer Island and Torry Island were typically smaller, had fewer leaves, and grew less rapidly than healthy plants. As a result, waterlettuce populations harboring large weevil infestations exhibited reduced vigor, and standing crop and coverage declined until waterlettuce was virtually eliminated from these waterbodies. Why the Port St. Lucie populations failed to increase to damaging levels has not been determined, though several hypotheses present themselves. Weed control agencies in southern Florida have cooperated to spread this weevil from Torry and Kreamer Islands to other waterways. Additional sites have become infested as the weevils disperse on their own.
- Agronomy, Horticulture and Aquiculture