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|Title:||Alligatorweed survey of ten southern states|
|Authors:||Aquatic Plant Control Research Program (U.S.)|
Cofrancesco, Alfred F.
Aquatic plant control
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: Alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.) is an exotic South American plant introduced into the United States prior to 1897. It rapidly developed into problem levels throughout most southern states, where it outcompetes native vegetation and interferes with navigation and recreational use of waterways. Three biological control agents, Agasicles hygrophila (Selman and Vogt), Amynothrips andersoni (O'Neill), and Vogtia malloi (Pastrana) were released in the United States between 1964 and 1970 for the control of alligatorweed. A review of the releases and population development of these insect species was conducted through 1972 by US Department of Agriculture scientists. The objectives of this study were to: (A.) determine the current extent of the alligatorweed population in each state and ascertain whether or not it occurred at problem levels, (B.) define the current population levels of biocontrol agents at selected original release sites and assess their impacts on the alligatorweed population, (C.) describe the current distribution of each species of biocontrol agent in each state, (D.) identify environmental factors influencing the effectiveness of each biocontrol agent, and (E.) provide recommendations for managers to enhance the effectiveness of each biocontrol agent in areas where control has not been achieved. Data indicate that alligatorweed is not a major problem throughout the southeastern United States; however, its population levels do vary between and within states. Louisiana, Florida, and Georgia have only minor alligatorweed problems, which generally are controlled by the biocontrol insects. Alligatorweed problems in Mississippi and Alabama vary greatly between the northern and southern portions of the states. In the northern portions of Mississippi and Alabama, alligatorweed causes problems, but the southern portions of these states have no alligatorweed problems. Alligatorweed occurs as a minor problem in South Carolina, Arkansas, and Tennessee. Texas and North Carolina also have minor problem levels of alligatorweed; however, certain environmental conditions often make these problems more severe. The distribution of each biocontrol agent varies among states. Both Agasicles and Vogtia were found in 7 of the 10 states surveyed. Agasicles were absent from Arkansas, North Carolina, and Tennessee, whereas Vogtia were absent from Arkansas, Georgia, and Tennessee. Alligatorweed was not found in Tennessee, so it was highly unlikely that any of the biocontrol agents would be found. Literature indicates that Agasicles regularly occur in Arkansas, but their population levels must be extremely low. The presence of Vogtia in states north, south, and west of Georgia indicates that Vogtia probably do occur in Georgia, even though they were not collected in the state. Amynothrips were found in only Florida, Louisiana, Mississippi, Alabama, and Texas, and their distribution was usually limited within each state. The Amynothrips population found in Alabama and Texas was due to recent releases, and no populations were found in other areas of these states. Florida, Louisiana, and Mississippi have established populations; however, their distribution is also somewhat limited. Extreme temperature and water fluctuations appear to be the two most important environmental factors influencing the effectiveness of the biocontrol agents. Agasicles are unable to regularly impact the aquatic morphotype of alligatorweed in the northern range. Increased Vogtia populations occur in the northern states late in the season when alligatorweed biomass is greatest. Biocontrol agents need to be used as tools for controlling alligatorweed. When the proper conditions exist, insects need to be rapidly introduced so that their growth and impact can be the most productive. In areas where insect populations are established, they must be monitored to ensure high population levels. Considerations should be taken to determine the availability of a mobile biocontrol agent that impacts the terrestrial morphotype of alligatorweed. NOTE: This file is very large. Allow your browser 3-5 minutes to download the file.
|Appears in Collections:||Miscellaneous Paper|