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Title: Final report on the overseas surveys (1981-1983) for insects to control Hydrilla
Authors: Fort Lauderdale Research and Education Center.
Aquatic Plant Control Research Program (U.S.)
Balciunas, Joseph K.
Keywords: Aquatic plant control
Aquatic weeds
Biological control
Hydrilla verticillata
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The geographic area of origin for the noxious exotic weed, hydrilla (Hydrilla verticillata), has not been pinpointed. Three extended collecting trips to Asia and Australia where hydrilla is considered to be native were made to catalog the natural enemies of this plant. During the 15 months spent overseas during these surveys, the strategy was to collect at as many different sites as time and funding would permit. Unlike in the United States, hydrilla rarely forms dense monocultures in these areas, and it was frequently difficult to locate. The lack of competitiveness and "weediness" by hydrilla in its native range is probably due, in most instances, to the action of natural enemies. These three surveys yielded 180 collections containing over 45 insect species which attack hydrilla. All 45 of these insects are either weevils, ephydrid flies, or aquatic moths, groups which are known to be herbivorous and host-specific. Insects which only occasionally damage hydrilla, such as caddisfly and midge larvae, are not included in the list. More intensive surveying would also multiply this number of candidate species. Compared to the handful of insect species found attacking hydrilla in the United States during an intensive multiyear survey, it is apparent that hydrilla in the United States is depauperate in natural enemies. This helps to account for hydrilla's rapid displacement of native plants in the United States. Since native competitors are absent, introduced biological control insects would have a high chance of becoming established in the United States. The control of hydrilla in the United States by introduced exotic insects now appears more probable, and the hydrilla biological control project should be intensified. Achieving a level of hydrilla control comparable to that observed overseas will probably require the introduction of a complex of insects (including leaf-miners, defoliators, stem-borers, and tuber feeders). The long-term nature and multispecies approach should be incorporated into the planning and funding of the hydrilla biocontrol project. The screening for possible introduction into the United States of insects already found during these surveys has begun and will continue. However, a more complete list of hydrilla's natural enemies is required to allow sound decisions in the future. This would require expanding the searches to areas not yet surveyed and conducting more intensive searches at the more promising of the areas previously visited. These areas, along with additional recommendations, are listed in this report.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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