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Title: | Genetic relationships among invasive Hydrilla (Hydrilla verticillata L.f. Royle) biotypes in the US and their implications for management |
Authors: | Harms, Nathan E. Williams, Dean A. Grodowitz, Michael Jay |
Keywords: | Aquatic plants--Control Vegetation Aquatic environments Aquatic ecosystems Hydrilla Genetics Biotypes Environmental management Aquatic Plant Control Research Program (U.S.) |
Publisher: | Engineer Research and Development Center (U.S.) |
Series/Report no.: | Technical Note (Aquatic Plant Control Research Program (U.S.)) ; no.ERDC/TN APCRP-BC-32 |
Abstract: | NTRODUCTION: Hydrilla verticillata L.f. Royle (hydrilla; Hydrocharitaceae), an invasive submersed plant native to Southeast Asia and Australia, was first introduced into the US through the aquarium trade in Florida in the 1950s (Schmitz et al. 1991). Hydrilla impacts freshwater resources in the US by its aggressive, canopy-forming growth that degrades aquatic ecosystems, limits recreation, fouls boat motors, and clogs irrigation and hydroelectric plants. In the US there are two recognized hydrilla biotypes: the dioecious biotype is generally found in the southeastern and south central US; whereas the monoecious biotype is mostly found in the central Atlantic and northeastern US (Madeira et al. 2000). The dioecious biotype has been present, and spreading, in the US since the first introduction over 50 years ago. In contrast, monoecious hydrilla is widely recognized as a relatively recent introduction, first identified in the northeastern United States in 1982 (Steward et al. 1984). Since the initial identification, monoecious hydrilla has been reported in Connecticut, Massachusetts, Maine, New York, and as far south as Georgia and Alabama. Additional populations of the monoecious biotype are known to be found in Washington and California (Madeira et al. 2000). Management of hydrilla is typically accomplished through mechanical, chemical, and biological means. Mechanical harvesting of hydrilla has been attempted over the years but it is typically cost prohibitive and results in production of additional plant propagules through fragmentation. Chemical applications include complexed copper, diquat, endothall, fluridone, and — more recently — imazamox, penoxsulam, bispyribac-sodium, and flumioxazin (Gallagher and Haller 1990, Netherland 2009). In the 1970s and 1980s, partly because of the successes of the Alternanthera philoxeroides (Mart.) Griseb. (alligatorweed) and the Eichhornia crassipes Kunth (water hyacinth) biological control programs, the United States Department of Agriculture (USDA) and the United States Army Corps of Engineers (USACE) began overseas searches for insect biological control agents of hydrilla in its native range (Bennett and Buckingham 2000). These surveys and subsequent host-specificity testing culminated in the release of four insect agents, Hydrellia pakistanae Deonier (Diptera: Ephydridae), H. balciunasi Bock, Bagous affinis Hustache (Coleoptera: Curculionidae), and B. hydrillae O’Brien in the late 1980s and early 1990s (Buckingham and Balciunas 1994). Because the initial foreign surveys for biological control agents were conducted before it was known that multiple biotypes were present in the US, it is not clear whether the surveyed plants in the native range were dioecious (present, at the time, in the US) or monoecious (not yet introduced into the US). This question has been raised by various authors in recent years (Grodowitz et al. 1997, Benoit 2011), and could partially explain the mixed results (i.e., some successes and some failures) in the hydrilla biocontrol program (Grodowitz et al. 2010). While recent foreign explorations of herbivores for dioecious hydrilla have taken place in Africa and southern China (Copeland et al. 2011, Copeland et al. 2012, Zhang et al. 2012), examination of monoecious plants for natural enemies has yet to take place. It has recently become apparent that monoecious hydrilla may be minimally affected by the current insect biocontrol agents available on dioecious hydrilla (Grodowitz et al. 2010), due to an apparent clash of monoecious hydrilla phenology (winter senescence and lack of water-column biomass) with overwintering requirements of the agents (H. pakistanae larvae utilize available water-column plant material to survive winter months). Because of this, it is important to begin searches for additional agents. A number of authors have suggested that both host specificity and efficacy of biocontrol agents should be highest in the source region of the invader and have recommended “biotype matching” of target plants and candidate natural enemies (e.g., Roderick and Navajas 2003, Wardill et al. 2005, Goolsby et al. 2006, Manrique et al. 2008). This strategy is predicated on the idea that host-specific natural enemies will be locally adapted to their hosts and that local adaptation of the herbivore will result in higher population growth rates and greater damage to their hosts (Hufbauer and Roderick 2005). For this reason, it is important to identify the geographic source of monoecious hydrilla. With refinement of molecular techniques, the genetic variability between and within hydrilla populations has been examined by various researchers and has led to a clearer understanding of the geographic origin of both hydrilla biotypes. The goal of this technical note is to summarize and report the most recent information available on the geographic origin of both hydrilla biotypes and discuss the implications of genetic differences with regard to management of hydrilla in the US. |
Description: | Technical Note |
Gov't Doc #: | ERDC/TN APCRP-BC-32 |
Rights: | Approved for public release; distribution is unlimited |
URI: | http://hdl.handle.net/11681/3896 |
Appears in Collections: | Technical Note |
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ERDC-TN-APCRP-BC-32.pdf | ERDC/TN APCRP-BC-32 | 829.67 kB | Adobe PDF | View/Open |