17 Phytophagous Insects, Fish, and Other Biological Controls 17.1 INTRODUCTION Mechanical and chemical methods (Chapters 12, 13, 14, 16, and 20) are the primary management procedures for nuisance aquatic plants. They are often successful, usually expensive, and frequently provide only relatively short-term control. There has been a widespread, sometimes justified, fear of herbicides. Mechanical/physical techniques can be slow, ineffective, subject to breakdowns, and may spread the infestation. Neither type of method is selective, but instead provides temporary elimination of most plants, including the target plant, usually producing habitat removal instead of restoration of the community to a prior and more desirable condition. Eight exotic aquatic plants have proliferated in lakes of North America and elsewhere. They are: Hydrilla (Hydrilla verticillata (L.f.) Royle), Water hyacinth (Eichhornia crassipes (Mart.) Solms-Laubach), Alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), Eurasian watermil- foil (Myriophyllum spicatum L.), Floating Fern (Salvinia molesta D.L. Mitchell), and Waterlettuce (Pistia stratiotes L.), curly leafed pondweed (Potamogeton crispus L), and Brazilian elodea (Egeria densa Planch. (= Anacharis densa (Planch.) Vict.). Their success is due to invasions of highly favorable, often disturbed, habitats where biological controls are limited or absent, rather than a response to eutrophication. The problem is acute in southern U.S. states where there is an abundance of shallow, warm, naturally fertile aquatic habitats, and a long growing season. The widespread economic damage and inconvenience caused by these plants, coupled with dissatisfaction with mechanical and chemical methods, has led to the development of biological controls, including phytophagous insects and fish, plant pathogens such as fungi and viruses, and allelopathy. Biological controls, including food web manipulations (Chapter 9) and use of barley straw for management of algal biomass, are not without problems, including slow response, inability to eradicate the nuisance plant or treat a problem area such as a beach, low predictability, and the potential to create additional problems if the biological control organism has unintended and undesirable impacts. This chapter describes some of these biological control methods, focusing primarily on aquatic plant management. Their deployment is recent, and there is much to be learned. Our reliance on mechanical and chemical methods has been necessary during the early years of aquatic plant control, and they continue to be important tools. The future may lie with integrating traditional techniques with biological ones, an approach requiring sustained efforts to better understand aquatic ecosys- tems, and to monitor closely those treated with any of these methods. Biological control differs substantially from mechanical, and especially chemical, techniques. The objective of biological control is to significantly reduce target plant biomass without eradication (which would also eradicate the biocontrol organism). The goals are to identify a biological agent specific to the target plant, to establish a dynamic equilibrium between this organism and the plant at an acceptable level of plant biomass, and to return the system to an earlier and more desirable community structure. Biocontrol is a suppression technique. There is no goal of plant elimination (Grodowitz, 1998). Plant biomass control will be achieved slowly, and ideally it will be very long lasting, economical, and the biocontrol organism itself will not become a nuisance. The principles Copyright © 2005 by Taylor & Francis of biological control of exotic pests, and the problems and concerns associated with them, continue to be debated (e.g., Hoddle, 2004; Louda and Stiling, 2004). There are two types of biological control. One is augmentive, where a naturally occurring (native or endemic) organism is identified and cultured, and individuals are added to the natural population at a particular site. An example is the milfoil weevil Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae), a herbivore that appears to have switched host preference from the native Myriophyllum sibiricum Komar (= M. exalbescens Fernald) to the exotic M. spicatum. The second approach, classical biocontrol, involves the addition of a herbivore or pathogen from the exotic plant’s native range. A series of research stages must occur that may end in the release of an exotic organism to control an exotic plant. The target plant is studied in its native range to identify promising species, and to determine whether they feed on or affect closely related and/or economically or ecologically important plants. Host-specific insects are imported under quarantine to a U.S. Department of Agriculture (USDA) facility in Gainesville, Florida. Here, host specificity and potential effectiveness are examined. Insects that prove to be safe for application may then be released from quarantine through authorization from the Animal and Plant Inspection Service (APHIS) of the USDA. Also, the U.S. Department of Interior can restrict the introduction of exotic species for biological control (Hoddle, 2004). Examples of this lengthy procedure are found in Buckingham and Balciunas (1994) and Buckingham (1998). Twelve insects have been released from quarantine in the U.S. for treatment of nuisance aquatic plants (Table 17.1). Plant pathogens from nuisance plant home ranges are still unavailable for application, but may be brought into the U.S. for study at the quarantine facility at Fort Detrick, Maryland (see later section). The following paragraphs describe the use of insects for control of four of the eight exotic nuisance aquatic plants in U.S. lakes. 17.2 HYDRILLA (HYDRILLA VERTICILLATA) Hydrilla verticillata (L. f.) Royle (= “hydrilla”) has caused great ecological and economic damage in the U.S. The dioecious biotype (plants have male or female flowers) was introduced to Florida by an aquarium dealer in about 1950; the monoecious biotype (each plant has male and female flowers) appeared in the late 1970s, possibly from Korea. Eradication is essentially impossible because plants reproduce from tiny fragments that are easily transported to other aquatic habitats, and from seeds, turions and tubers that are resistant to drought, cold, and herbicides. Thick mats TABLE 17.1 Insect Species Released for Biological Control of Aquatic Plants Target Plant Insect Alligatorweed Amynothrips andersoni O’Neill Alligatorweed Vogtia malloi Pastrana Alligatorweed Agasicles hygrosphila Selman and Vogt Water lettuce Neohydronomus affinis Hustache Water lettuce Spodoptera pectinicornis (Hampson) Hydrilla Hydrellia pakistanae Deonier Hydrilla Bagous affinis Hustache Hydrilla Bagous hydrillae O’Brien Hydrilla Hydrellia balciunasi Bock Water hyacinth Arzama densa Walker Water hyacinth Sameodes albiguttalis (Warren) Water hyacinth Neochetina eichhorniae Warner Copyright © 2005 by Taylor & Francis form in shallow water, or in clear deep water, whether eutrophic or oligotrophic (Buckingham and Bennett, 1994; Balciunas et al., 2002). Hydrilla is one of the most troublesome aquatic plants in the southeastern U.S., causing millions of dollars in damage to irrigation operations, hydroelectric power generation, and recreational activities. Infested lakes can become closed to most uses. There is now concern about the northward spread of the monoecious biotype. It is found at 55° N latitude in Europe and could survive in any U.S. state (Balciunas et al., 2002). Newly established infestations of the monoecious biotype in Pennsylvania, Connecticut and Washington states are not new foreign introductions, as demon- strated by randomly amplified polymorphic DNA analysis. The plant is found in at least 16 U.S. states and 185 drainage basins (Madeira et al., 2000). The monoecious biotype has higher production of shoots (source of fragments) at lower temperatures, than the dioecious biotype (Steward and Van, 1987; McFarland and Barko, 1999). Global climate change could be a factor in enhancing its northward spread. If hydrilla spreads northward, it will be important for lake managers to recognize and attempt to eradicate it immediately. It is difficult to distinguish from other species of Hydrocharitaceae. There are two native members of this family, Elodea canadensis and E. nuttalii and one exotic, Egeria densa, which look like hydrilla. Hydrilla has marginal teeth on the leaves that are visible without a lens, whereas the other species require a hand lens to see the fine marginal teeth (Dressler et al., 1991; Borman et al., 1997). Hydrilla management typically involves either grass carp (= white amur, see later paragraphs) introduction or herbicide application. However, classical biocontrol agents are also used. Two weevils (Coleoptera: Curculionidae), Bagous affinis Hustache and B. hydrillae O’Brien, were released in Florida in 1987 and 1991, respectively, but neither was successful (Buckingham and Bennett, 1994; Balciunas et al., 2002). Two ephydrid flies (Diptera: Ephydridae), Hydrellia paki- stanae Deonier and H. balciunasi Bock, were released in 1987 and 1989, respectively. H. balciunasi has established at only a few sites, apparently due to high wasp parasitism, poor host plant food quality, and possible genetic differences between hydrilla in the U.S. and hydrilla in Australia, where the flies are native (Grodowitz et al., 1997). H. pakistani produced significant decreases in hydrilla, along with recovery of native plants. Successful biocontrol of hydrilla with this insect may be slow. For example, insects were released in 1992 into Lake Seminole, Georgia. Hydrilla declines were noted in 1997 and large-scale decreases were evident in 1999 (Balciunas et al., 2002). The impact on hydrilla may be enhanced by combining insect application with a pathogenic fungus, Fusarium culmorum (Shabana et al., 2003). The success of this insect may be influenced by the nutritional status of the hydrilla host. Plants with low tissue N or with tough leaves lead to higher insect mortality and impaired development (Wheeler and Center, 1996), suggesting that host plant adaptation to the insect may be another important factor in unsuccessful biocontrol. Presently, classical biocontrol of hydrilla is in a developmental stage, and use of grass carp, harvesters, and herbicides remain reliable and effective choices. More research is needed, including overseas surveys, to locate biocontrol agents and to assess factors influencing establishment and growth of biocontrol organisms. 17.3 WATER HYACINTH (EICHHORNIA CRASSIPES) Water hyacinth, introduced to the U.S. in the 1880s, has created much economic and environmental damage and some consider it to be “the world’s most troublesome aquatic weed” (Center et al., 1999). This plant is a nuisance throughout tropical and subtropical areas of the Earth, and has posed human life-threatening situations (e.g., trapped boats, collapsed bridges, enhanced mosquito habi- tat). It is a floating plant with large leaves, an attractive flower, and very high growth rates, leading to a dense, interconnected mat. Under favorable conditions, complete surface coverage of a pond or small lake is possible, and wind-drifted mats trap boats and close dock areas. Water hyacinth can reproduce via seeds that remain viable in aquatic sediments for 15–20 years, but fastest Copyright © 2005 by Taylor & Francis population growth is through vegetative processes (Center et al., 2002). Mechanical and chemical controls have met with varying degrees of success, in part because rapid re-growth follows treatment. Biocontrol agents were investigated in Argentina in the 1960s and 1970s, leading to importation under quarantine of three insects that were later released after extensive testing. Argentina was chosen because water hyacinth is native to South America and because its climate is similar to the infested areas of North America (Center, 1982). The imported insects are: the moth Niphograptera (= Sameodes) albiguttalis (Warren) (Lepidoptera: Pyralidae), and the beetles Neochetina eichhor- niae Warner and N. bruchi Hustache (Coleoptera: Curculionidae). The mite Orthogalumna tere- brantis Wallwork (Acarina: Galuminidae), a native North American species, was also suggested. N. eichhorniae and N. bruchi were released in Florida in 1972 and 1974, respectively, and the moth was released in 1977 (Center et al., 2002). The beetles are host specific and both adults and larvae affect the plants. Eggs are embedded in plant tissues. Tiny (2 mm) larvae appear in the spring and burrow into leaf petioles, causing wilting and leaf loss from the stems. Mature larvae (8 to 9 mm) enter the stem and attack the apical meristem. Pupae are found attached to roots below the water surface. The adults attack the youngest leaves, eating epidermal cells, which provide sites for microorganisms to augment plant damage. Leaf death occurs slightly faster than leaf renewal, leading to a net loss of leaves. Water hyacinth requires a minimum number of leaves in order to float, and when leaf loss exceeds this limit, plants sink and die (Center et al., 1988). Classical biocontrol of water hyacinth is highly successful, as illustrated by results from Louisiana, where the infestation averaged 500,000 ha during the fall months of 1974 to 1978. N. eichhorniae was released in southeastern states in 1974 to 1976, becoming established by 1978. N. bruchi was released in 1975 and N. albiguttalis in 1979. By 1980, insect impact was evident, reducing coverage to 122,000 ha. Coverage in 1999 was well below 100,000 ha. Other factors, including herbicide use, saltwater intrusions, and weather do not account for the extent of this decline (Figure 17.1) (Center et al., 2002). A sustained threshold density of 1.0 insect/plant for 6 months, followed by a peak of 3 or more/plant, is needed to reduce plant coverage. This density is affected by season, plant vigor, and plant pathogens. A natural cycling of plant and insect abundance should develop in which plant FIGURE 17.1 Data from Louisiana, showing reduced waterhyacinth cover and limited annual growth after introduction of Neochetina eichhorniae in 1974, N. bruchi in 1975, and Niphograpta albiguttalis in 1979. (From Center, T.D. et al. 2002. In: R. Van Driesch et al. (Tech. Coord.), Biological Control of Invasive Plants in The Eastern United States. U.S. Department of Agriculture Forest Service Pub. FHTET-2002-04. Bull. Distribution Center, Amherst, MA. Chapter 4.) 800 700 600 500 400 300 200 100 0 Area infested (ha, × 1000) 1999199419891984 Year 19791974 Spring Fall Copyright © 2005 by Taylor & Francis density increases for 2 to 3 years and then declines as the slower growing insect biomass reaches threshold density. Plant biomass then remains low for some period, leading to reduced insect density, plant recovery, and so forth. Plant or insect eradication, except on a small scale, is unlikely. Little is known about other mortality sources (e.g., fish, birds) of insect biocontrol agents and is a major research area (Sanders and Theriot, 1986). Successful insect use to control water hyacinth illustrates important facts about biocontrol. First, the process is slow, does not produce eradication (e.g., Figure 17.1), and provides long-term, low cost reduction in biomass. Successful biocontrol returns the water resource to all uses. These points are important because 2,4-D, an effective herbicide on water hyacinth, is not available to many tropical and subtropical people. Second, insect control of aquatic plants is not compatible with plant removal via harvesting or herbicides. Chemical and mechanical treatments remove immobile eggs, larvae and pupae so that when plant re-growth occurs from seeds and fragments, few insects remain to suppress the new growth. Long-term control with insects is more likely without intense management (Center, 1987). An integrated approach, where several large lake areas are not sprayed or cut, may allow survival of enough insects to re-infest new growth (Haag, 1986; Haag and Habeck, 1991). Because there may be public pressure for immediate relief from an infestation, significant research areas are to identify herbicides and adjuvants that are non-toxic to biocontrol insects, and to develop management protocols that allow for treatment of critical lake use areas, but protect the insects for long-term plant suppression (Center et al., 1999). Water hyacinth appears to be spreading northward from southeastern U.S. states, and an important research area is to identify cold tolerant biocontrol agents (Center et al., 2002). 17.4 ALLIGATORWEED (ALTERNANTHERA PHILOXEROIDES) Classical insect control of alligatorweed is very successful. The plant was introduced to the U.S. in the 1880s. It spread rapidly through southeastern states, forming interwoven mats, some as thick as 1 m, sometimes over an entire pond, lake, or canal. Alligatorweed is a rooted, perennial plant that reproduces vegetatively in the U.S. and is capable of becoming terrestrial if a habitat dries (Buckingham, 2002). Investigations in Argentina, followed by studies under quarantine in the U.S., led to releases of three insects (Maddox et al., 1971): a flea beetle Agasicles hygrophila Selman and Vogt (Coleoptera: Curculionidae), a thrip Amynothrips andersoni O’Neill (Thysanoptera: Phlaeothripi- dae), and a moth Vogtia malloi (Pastrana) (Lepidoptera: Pyralidae), released in 1964, 1967 and 1971, respectively. Agasicles has been so successful in controlling alligatorweed that the plant is no longer a nuisance, except in local areas. Five factors led to its success: (1) high reproductive potential, (2) a life history spent on or in alligatorweed, making it less vulnerable to insectivores, (3) complete dependence or specificity on alligatorweed, (4) high mobility and dispersion power, and (5) high tolerance to some chemicals, including certain insecticides (Spencer and Coulson, 1976). Larvae and adults feed on leaves, and larvae bore into the stem to pupate. Vogtia and Agasicles were successfully introduced into Tennessee, southern Alabama, Louisi- ana, Georgia, North and South Carolina, Texas, and Arkansas. The terrestrial form of alligatorweed is not controlled by these species, though the flightless thrip Amynothrips can be locally effective but not widely distributed. Temperature and water level fluctuations affect the success of Agasicles. Greatest effectiveness in controlling alligatorweed occurs where weather permits peak populations to develop by June. The northern limit of effectiveness corresponds roughly with a mean January temperature of 12°C. There is no winter diapause in Agasicles so it is eliminated in northern latitudes, or in sites where alligatorweed is frozen back to the shoreline so that beetles cannot feed. The southern limit occurs where summer dormancy to escape intense heat is so extended that no fall population peak occurs Copyright © 2005 by Taylor & Francis (Spencer and Coulson, 1976). Flooding eliminates insects and droughts stimulate the terrestrial form of the plant, eliminating alligatorweed as a food source for flea beetles and stem borers (Cofrancesco, 1984). The flea beetle’s effectiveness is enhanced by Vogtia and Amynothrips. There are also possi- bilities for combining insect use with herbicide pre-treatment (Gangstad et al., 1975) or with plant pathogens or mechanical methods. Unquestionably, insects have been successful in alligatorweed control, eliminating or greatly reducing the need for machines and chemicals, and allowing native plant species to return. Unfortunately, another exotic, such as water hyacinth or hydrilla might replace the controlled species, but insect control of these species, especially water hyacinth, is also possible. 17.5 EURASIAN WATERMILFOIL (MYRIOPHYLLUM SPICATUM) Eurasian watermilfoil (“milfoil,” EWM), a native to Asia, Africa and Europe, was introduced to North America between the 1880s and 1940, and spread to nearly every state and three southern Canada provinces. It has displaced native milfoils and other submersed species, in part because it forms a distinct canopy on the lake surface, shading understory species. EWM spreads via fragments, infesting an entire lake or pond, or dispersing to new habitats through lake outflows or human activities. Seeds are formed in spike-like flowers extending above the water surface, but the primary reproduction method is vegetative (Creed, 1998; Johnson and Blossey, 2002). This exotic, perhaps more than any other aquatic plant in North America, has produced extensive biodiversity declines, high treatment costs, and loss of aesthetic and recreational attributes of lakes and reservoirs. Traditional milfoil management methods (harvesting and herbicides) have not always been satisfactory, in part because plants re-grow rapidly or harvesters spread fragments to uninfested lake areas. Grass carp (see later sections) do not prefer them. Sudden, unexplained declines in heavily infested lakes suggested that biological agents, including insects, could be responsible. While searches for biocontrol organisms in milfoil’s native range (for classical biocontrol) have not been successful, native and naturalized insects in North America that consume milfoil were investigated for their potential to provide augmentive control. However, there can be problems with augmentive control, including: (1) native insect populations may not remain at the high densities needed (perhaps due to long-established predator-prey and other density regulation processes), (2) native insect life histories may be “out of phase” with the exotic plant’s, and (3) augmentation is expensive (Creed and Sheldon, 1995). To be an effective augmentive biocontrol agent, the insect must be nearly monophagous on the exotic plant. Otherwise, the insect may prefer and disperse to non-target plants it evolved with. If the exotic plant was not controlled by native insects when it invaded, then use of these insects for augmentive control could be unsuccessful. Despite these concerns, several native and naturalized insect species have been investigated. Triaenodes tarda Milner (Trichoptera: Leptoceridae) and Cricotopus myriophylii Oliver n. sp. (Diptera: Chironomidae) damage milfoil in British Columbia lakes, but have not been cultured and used in augmentation (Kangasniemi, 1983; Oliver, 1984; MacRae et al., 1990).The moth Acentria ephemerella Denis and Schiffermuller (= A. nivea Olivier) (Lepidoptera: Pyralidae), an invader from Europe, is established and ubiquitous in eastern and central North America (Johnson et al., 1998), and is a major source of EWM mortality when larvae reach a density of 6–8 per 10 apical tips. The native weevil Litodactylus leucogaster (Marsham), also associated with milfoil, appears to have little potential for biocontrol (Painter and McCabe, 1988; Johnson and Blossey, 2002). The impacts of Litodactylus, and especially Acentria, on milfoil in a group of Ontario lakes, are illustrated in Figure 17.2. The native milfoil weevil Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae) has been associated with EWM declines (e.g., Kangasniemi, 1983), and recent laboratory and field experiments demonstrated that the association was causal. This insect is available commercially for field augmentations (e.g., Hilovsky, 2002). A. ephemerella and E. Copyright © 2005 by Taylor & Francis FIGURE 17.2 Insect grazing damage estimates for Ontario lakes and the proportion of weevil larvae (Lito- dactylus leucogaster) and moth larvae (Acentria nivea) and cases observed. (From Painter, D.S. and K.J. McCabe. 1988. J. Aquatic Plant Manage. 26: 3–12. With permission.) Lower rideau Newboro Indian Opinicon Lower buckhorn Grazing damage rating 2 3 4 5 Proportion of weevil’s found Proportion of moths found Stony Katchewanooka Sturgeon Buckhorn Scugog Upper rideau Pigeon Rice Grazing damage rating 2 3 4 5 Proportion of weevil’s found Proportion of moths found Chemung Copyright © 2005 by Taylor & Francis lecontei have potential as augmentive biocontrol agents for EWM in North America and are discussed further in subsequent sections. Acentria is the dominant herbivore on EWM in Cayuga Lake, New York. The larvae mine leaflets and feed on the apical meristem, eventually removing the meristem tip as the cocoon is formed, preventing canopy formation and eliminating a competitive advantage over native plants with lower growth forms. The larvae overwinter in Ceratophyllum demersum stems (Johnson et al., 1998; Johnson and Blossey, 2002). One effect of EWM apical tip removal by insects is that this is the site of most intense production of the algicidal substance tellimagrandin II (Gross, 2000). Reduced production of this compound leads to increased epiphyte growth on leaves and possibly to shading and reduced photosynthesis, an effect similar to fish predation on epiphyte-grazing snails (Chapter 9). The effectiveness of augmenting Acentria populations is unknown, although there have been experimental releases in New York state. The larvae are generalist feeders in the laboratory but select for and do serious damage to EWM in the field (Johnson et al., 1998). Earlier field obser- vations (Creed and Sheldon, 1995) indicated that Acentria was associated with milfoil declines in Brownington Pond, Vermont. Acentria exhibits reduced growth on milfoil, compared to Potamo- geton, possibly due to the high phenolic content of milfoil leaves (Choi et al., 2002). Additional research is needed, mainly with methods to grow large quantities of Acentria for field augmentation, and with observations of effectiveness. E. lecontei apparently evolved with the North American native milfoil Myriophyllum sibiricum Kom. (= M. exalbescens Fern.), but the weevil prefers EWM in host specificity tests (Newman et al., 1997; Solarz and Newman, 2001). Females lay eggs on apical meristems. While adults feed on leaves, the larvae have the greatest negative effects, eating about 15 cm of the meristem, and eventually mining the stem and destroying vascular tissue. Larvae move about 0.5 to 1.0 m from the apical meristem, burrow into the stem, and pupate. The plant’s leaf-stem-root connection may be eliminated leading to nutrient deficiencies and less carbohydrate storage in roots. The larvae may also create optimum conditions for fungal and bacterial infections of the plant. Normally there can be 4 to 5 generations per summer. Adults crawl or fly to the shore in autumn, overwintering in drier leaf litter, up to 6 m from shore. Adults return to the lake, beginning at ice-out (Creed, 2000; Mazzei et al., 1999; Newman et al., 2001; Johnson and Blossey, 2002; Newman, 2004;). Attempts to eliminate plants with harvesting, herbicides, or grass carp usually reduce insect density to ineffective low levels (i.e., Sheldon and O’Bryan, 1996). R.P. Creed Jr., S.P. Sheldon, and co-workers (e.g., Creed et al., 1992; Creed and Sheldon, 1993, 1995) were among the first to examine weevil impacts on EWM. Laboratory and field enclosure experiments demonstrated that Acentria and especially E. lecontei reduced EWM growth. Field observations showed an association of the insects with milfoil declines, and suggested that the weevil was most damaging. The decline of EWM in Cenaiko Lake, Minnesota appears to be the first demonstration that it was caused by the presence of E. lecontei, because there was no evidence of fungal infection and A. ephemerella and the midge Cricotopus myriophylli were associated with other plants. Acentria may have prevented milfoil resurgence at this lake (Newman and Biesboer, 2000). A key feature of successful insect biocontrol is host specificity. E. lecontei evolved with North American milfoils, but has very high preference for the exotic EWM. Weevils distinguish between exotic and native milfoil, possibly because adult weevils can detect a substance in EWM at distances up to 10 cm in still water, inducing preference for EWM. E. lecontei has higher egg-laying and development rates on EWM, and greater adult mass than on other species (Solarz and Newman, 2001; Newman, 2004). No-choice experiments with nine non-milfoil submersed species demon- strated that the weevil did not damage these plants, laid no eggs, and survived poorly (Sheldon and Creed, 1995). Thus E. lecontei is host-specific, having abandoned native milfoils where choice is possible. An effective density of E. lecontei is in the range of 50–100/m 2 , about two adults, larvae, eggs or pupae/stem (Creed and Sheldon, 1995; Newman and Biesboer, 2000). Copyright © 2005 by Taylor & Francis Factors regulating weevil density are poorly known. In a Minnesota lake, black crappie (Pomoxis nigromaculatus) and perch (Perca flavescens) consumed no life stage, while bluegills (Lepomis macrochirus) consumed adults and larvae, but not pupae. Bluegills could be a major mortality source with low insect and high fish densities. Odonate larvae are apparently unsuccessful larval predators (Sutter and Newman, 1999). More research is needed on weevil predators. Adults could be especially vulnerable in the fall as they move to shore to overwinter (Newman et al., 2001). Undisturbed shoreline areas, with no insecticide residuals, are apparently essential for successful overwintering. Lawns manicured to the lake’s edge are unlikely to provide suitable overwintering sites, though this has not been investigated. Acentria and E. lecontei clearly have negative impacts on milfoil. They rarely occur as co- dominants, suggesting competition (Johnson et al., 1998) and their use for biocontrol depends on which species can be easily cultured. At this time, only the weevil is being cultured for control purposes. Another question concerns the efficacy of the weevil in southern U.S. lakes and reservoirs, well away from their established range (Creed, 2000). High summer temperatures (> 35°C) in southern lakes and low temperatures (< 18°C) in more northern lakes may limit effectiveness to mid-latitude North America (Mazzei et al., 1999). Currently, E. lecontei is used to augment natural populations, but there are few long-term evaluations. There were no milfoil declines in Vermont that could be attributed to widespread augmentations with the weevil (Crosson, 2000 in Madsen et al., 2000), but preliminary data from 12 Wisconsin lakes suggest some control in the first year of augmentation (Jester et al., 2000). In summary, insects are effective, but they are slow and do not lead to eradication of target plants. Severe infestations can be reduced with insects, and when used with herbicides in a way that preserves an insect “reservoir,” there can be longer-term control. What other native insects could be used for aquatic plant control? Basic lake ecological research must continue. 17.6 GRASS CARP 17.6.1 H ISTORY AND RESTRICTIONS The grass carp, or white amur (Ctenopharyngodon idella (Val.) (Cyprinidae) is native to the large rivers of China and Siberia. The controversy in the U.S. over this exotic fish for aquatic plant control stems from the history of its introduction, its subsequent escape to North American rivers, and its expected impacts on lakes and reservoirs. It was shipped to the Fish Farming Experimental Station in Arkansas, and to Auburn University, from Malaysia in 1963. Between 1970 and 1976, 115 lakes and ponds in Arkansas were stocked, including Lake Conway, a hydrologically open system. Free-ranging fish were discovered outside of Arkansas in 1971, all from the 1966 age class (Guillory and Gasaway, 1978). Unlike the introduction of exotic insects to U.S. waters for plant control, grass carp were introduced without rigorous preliminary studies under quarantine. It should have been predicted that this “generalist” herbivore would have many negative features. It is likely that grass carp importation to the U.S. would not receive authorization by the U.S. Department of Agriculture if permission had been requested in more recent times. A scientific effort to understand the beneficial and harmful effects was launched after their broadcast to the waters of North America, a classic example of the “stock and see” mentality (Bain, 1993) so common with importation of exotic plants and animals. There have been many concerns about impacts on aquatic habitats where plants are desirable, and about their potential to enrich lake waters or to interfere with game fish or other biota. Some states prohibit their use, or have restricted use to the sterile triploid fish (Table 17.2). There has been a general restriction on importation and release in Canada, although triploids are under investigation in some provinces. Grass carp are popular, largely because they can provide low cost, long-term plant control, with acceptable negative impacts for some lake users. For example, a lake can become completely Copyright © 2005 by Taylor & Francis accessible for boating and swimming, though this may be at the expense of many lake and lake shore species, and an increase in trophic state. The purpose of this section is to provide lake managers with the information to make informed decisions about grass carp use. 17.6.2 BIOLOGY OF GRASS CARP Grass carp exhibit an unusual metabolic strategy. Their aerobic metabolic rate is about half that of many fish, but their average consumption rate (at 21°C or higher) as adults is about 50–60% of body weight/day, and may equal body weight/day in small (< 300 g) fish (Osborne and Riddle, 1999). This rate is two to three times that of carnivorous fish. Their low metabolism and high consumption rates offset their low assimilation efficiency, which is about one third that of carniv- orous fish (Wiley and Wike, 1986). Young grass carp are omnivorous, perhaps as a means of obtaining adequate protein (Chilton and Muoneke, 1992). Food assimilation decreases with increas- ing fish size and increases with increasing temperature. Up to 74% of ingestion is defecated, providing a significant load of partially digested organic matter and nutrients to the sediments. An energy budget for adult triploid carp is (Wiley and Wike, 1986): 100 I = 21 M + 67 E + 12 G where I = ingestion, M = metabolism, E = egestion, and G = growth The feeding rate is temperature dependent. They apparently do not feed at temperatures below 3°C, while active feeding begins at 7–8°C, and peak feeding is at 20–26°C (Chilton and Muoneke, 1992; Opuszynski, 1992). There may be regional acclimation so that fish in temperate climates, for example, begin feeding at lower temperatures, an important factor in stocking models (Leslie and Hestand, 1992). Triploid fish have a consumption rate that is about 90% of diploid fish. Average growth rates are 9–10 cm/year as juveniles, decreasing to 2–5 cm/year as adults (Chilton and TABLE 17.2 State Regulations on Possession and Use of Grass Carp A. Diploid (Able to Reproduce) and Triploid (Sterile) Permitted Alabama Hawaii Kansas Oklahoma Alaska Iowa Mississippi New Hampshire Arkansas Idaho Missouri Tennessee B. Only 100% Triploids permitted California Illinois New Jersey South Dakota Colorado Kentucky New Mexico Texas Florida Lousiana North Carolina Virginia Georgia Montana Ohio Washington Nebraska South Carolina West Virginia C. 100% Triploids Permitted for Research Only New York Oregon Wyoming D. Grass Carp Prohibited Arizona Maryland North Dakota Vermont Connecticut Massachusetts Pennsylvania Indiana Minnesota Wisconsin Maine Nevada Utah Copyright © 2005 by Taylor & Francis [...]... A.C and H.R King 1984 Large-scale Operations Management Test for Use of the White Amur for Control of Problem Plants Report 5 Synthesis Report Tech Rept A-7 8-2 U.S Army Corps Engineers, Vicksburg, MS Miller, H.D and R Potts 1982 Large-Scale Operations Management Test of the Use of the White Amur for Control of Problem Aquatic Plants; Report 3 Second Year Poststocking Results Vol VI: The Water and Sediment... Kirk and Socha, 2003), to at least 15 years in Florida lakes (Colle and Shireman, 1994) The Lake Conway, Florida study (Miller and Potts, 1982; Miller and Boyd, 1983; Miller and King, 1984) is a detailed examination of grass carp impacts Mean BOD, and filterable and TP concentrations decreased, and ammonia and chl a increased, compared to pre-stocking baseline data Algal populations were double those of. .. isolation Science 140: 679–680 Sanders, D.R and E.A Theriot 1986 Large-Scale Operations Management Test (LSOMT) of Insects and Pathogens for Control of Waterhyacinth in Louisiana Vol II Results for 1982–1983 Tech Rept A8 5-1 U.S Army Corps Engineers, Vicksburg, MS Schuytema, G.S 1977 Biological Control of Aquatic Nuisances — A Review USEPA-600/ 3-7 7-0 84 Shabana, Y.M., J.P Cuda and R Charudattan 2003 Combining... MI FWS/UBS-80/43 Conway, K.E 1976a Cercospora rodmanii, a new pathogen of water hyacinth with biological control potential Can J Bot 54: 1079–1083 Conway, K.E 1976b Evaluation of Cercospora rodmanii as a biological control of water-hyacinths Phytopathology 66: 914– 917 Cooke, G.D and R.H Kennedy 1989 Water Quality Management for Reservoirs and Tailwaters Report I In-reservoir Water Quality Management. .. Herlong and M.A Mallen 1992 Establishment and impact of redbelly tilapia in a vegetated cooling reservoir J Aquatic Plant Manage 30: 28–35 Desjardins, P.R 1983 Cyanophage: History and likelihood as a control In: Lake Restoration, Protection and Management USEPA 440/ 5-8 3-0 01 USEPA pp 242–248 Drenner, R.W., K.D Hambright, G.L Vinyard, M Gophen and U Pollingher 1987 Experimental study of size-selective... Studies on the Use of Fungal Pathogens for Control of Hydrilla verticillata (L.f.) Royle Tech Rept A-9 1-4 U.S Army Corps Engineers, Vicksburg, MS Kangasniemi, B.J 1983 Observations on herbivorous insects that feed on Myriophyllum spicatum in British Columbia In: Lake Restoration, Protection and Management USEPA-440/ 5-8 3-0 01 USEPA pp 214–219 Killgore, K.J., J.P Kirk and J.W Folz 1998 Response of littoral fishes... insects: State regulatory and management issues J Aquatic Plant Manage 38: 121–124 Mallison, C.T., R.S Hestand III and B.Z Thompson 1995 Removal of triploid grsss carp with an oral rotenone bait in two central Florida lakes Lake and Reservoir Manage 11: 337–342 Martinez-Jimenez, M and R Charudattan 1998 Survey and evaluation of Mexican native fungi for potential biocontrol of waterhyacinth J Aquatic... and J Boyd 1983 Large-Scale Management Test of the Use of the White Amur for Control of Problem Aquatic Plants; Report 4 Third Year Poststocking Results Vol VI: The Water and Sediment Quality of Lake Conway, Florida Tech Rept A-7 8-3 U.S Army Corps Engineers Jacksonville, Florida Miller, A.C and J.L Decell 1984 Use of White Amur for Aquatic Plant Management Instruct Rep A-841 U.S Army Corps Engineers,... tens of thousands of fish to large, hydrologically open systems Grass carp can be more easily removed from ponds, their escape can be prevented, and plant eradication will have little impact on waterfowl and other lake species The “all-or-none” response to stocking occurs in small lakes, but plant elimination may not produce the extensive negative impacts of eradication in large multi-use lakes 17. 6.6... overview of the use and efficacy of triploid grass carp Ctenopharyngodon idella as a biological control of aquatic macrophytes in Oregon and Washington state lakes In: Proceedings, Grass Carp Conference U.S Army Corps Engineers, Vicksburg, MS Pine, R.T and W.J Anderson 1991 Plant preferences of triploid grass carp J Aquatic Plant Manage 29: 80–82 Pine, R.T., L.W.J Anderson and S.S.O Hung 1989 Effects of . declines, high treatment costs, and loss of aesthetic and recreational attributes of lakes and reservoirs. Traditional milfoil management methods (harvesting and herbicides) have not always been satisfactory,. California, Pacific Northwest United States, and New Zealand) (Chapman and Coffey, 1971; Swanson and Bergerson, 1988; Pine and Anderson, 1991; Leslie and Hestand, 1992). Eurasian watermilfoil (Myriophyllum. (Miller and Potts, 1982; Miller and Boyd, 1983; Miller and King, 1984) is a detailed examination of grass carp impacts. Mean BOD, and filterable and TP concentrations decreased, and ammonia and chl