RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 17 pptx

Biological control differs substantially from mechanical, and especially chemical, techniques.The objective of biological control is to significantly reduce target plant biomass without

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 managementprocedures for nuisance aquatic plants They are often successful, usually expensive, and frequentlyprovide 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, andmay spread the infestation Neither type of method is selective, but instead provides temporaryelimination of most plants, including the target plant, usually producing habitat removal instead ofrestoration 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 aresponse 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 withdissatisfaction with mechanical and chemical methods, has led to the development of biologicalcontrols, including phytophagous insects and fish, plant pathogens such as fungi and viruses, andallelopathy Biological controls, including food web manipulations (Chapter 9) and use of barleystraw 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 thepotential to create additional problems if the biological control organism has unintended andundesirable impacts

This chapter describes some of these biological control methods, focusing primarily on aquaticplant management Their deployment is recent, and there is much to be learned Our reliance onmechanical 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 techniqueswith 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 agentspecific 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 desirablecommunity 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 longlasting, economical, and the biocontrol organism itself will not become a nuisance The principles

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 toidentify promising species, and to determine whether they feed on or affect closely related and/oreconomically 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 specificityand potential effectiveness are examined Insects that prove to be safe for application may then bereleased 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 exoticspecies for biological control (Hoddle, 2004) Examples of this lengthy procedure are found inBuckingham and Balciunas (1994) and Buckingham (1998) Twelve insects have been releasedfrom quarantine in the U.S for treatment of nuisance aquatic plants (Table 17.1) Plant pathogensfrom nuisance plant home ranges are still unavailable for application, but may be brought into theU.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 exoticnuisance 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 femaleflowers) appeared in the late 1970s, possibly from Korea Eradication is essentially impossiblebecause 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

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

form in shallow water, or in clear deep water, whether eutrophic or oligotrophic (Buckingham andBennett, 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 recreationalactivities Infested lakes can become closed to most uses There is now concern about the northwardspread 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 inPennsylvania, 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 andVan, 1987; McFarland and Barko, 1999) Global climate change could be a factor in enhancing itsnorthward 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 foodquality, 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 insectmay be slow For example, insects were released in 1992 into Lake Seminole, Georgia Hydrilladeclines 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 higherinsect mortality and impaired development (Wheeler and Center, 1996), suggesting that host plantadaptation 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, includingoverseas surveys, to locate biocontrol agents and to assess factors influencing establishment andgrowth of biocontrol organisms

17.3 WATER HYACINTH (EICHHORNIA CRASSIPES)

Water hyacinth, introduced to the U.S in the 1880s, has created much economic and environmentaldamage 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 posedhuman 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 hyacinthcan reproduce via seeds that remain viable in aquatic sediments for 15–20 years, but fastest

population growth is through vegetative processes (Center et al., 2002) Mechanical and chemicalcontrols 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 importationunder quarantine of three insects that were later released after extensive testing Argentina waschosen 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 brantis Wallwork (Acarina: Galuminidae), a native North American species, was also suggested.

tere-N eichhorniae and tere-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 inplant tissues Tiny (2 mm) larvae appear in the spring and burrow into leaf petioles, causing wiltingand leaf loss from the stems Mature larvae (8 to 9 mm) enter the stem and attack the apicalmeristem Pupae are found attached to roots below the water surface The adults attack the youngestleaves, 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 hyacinthrequires a minimum number of leaves in order to float, and when leaf loss exceeds this limit, plantssink 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 ormore/plant, is needed to reduce plant coverage This density is affected by season, plant vigor, andplant 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.)

1989 1984

Year 1979

1974

Spring Fall

density increases for 2 to 3 years and then declines as the slower growing insect biomass reachesthreshold 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 majorresearch 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 Thesepoints are important because 2,4-D, an effective herbicide on water hyacinth, is not available tomany tropical and subtropical people Second, insect control of aquatic plants is not compatiblewith plant removal via harvesting or herbicides Chemical and mechanical treatments removeimmobile 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 likelywithout intense management (Center, 1987) An integrated approach, where several large lake areasare 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, significantresearch 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 theinsects for long-term plant suppression (Center et al., 1999) Water hyacinth appears to be spreadingnorthward from southeastern U.S states, and an important research area is to identify cold tolerantbiocontrol 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 plantthat 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) completedependence or specificity on alligatorweed, (4) high mobility and dispersion power, and (5) hightolerance to some chemicals, including certain insecticides (Spencer and Coulson, 1976) Larvaeand 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 occurswhere summer dormancy to escape intense heat is so extended that no fall population peak occurs

(Spencer and Coulson, 1976) Flooding eliminates insects and droughts stimulate the terrestrialform 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 plantpathogens or mechanical methods Unquestionably, insects have been successful in alligatorweedcontrol, eliminating or greatly reducing the need for machines and chemicals, and allowing nativeplant species to return Unfortunately, another exotic, such as water hyacinth or hydrilla mightreplace the controlled species, but insect control of these species, especially water hyacinth, isalso possible

17.5 EURASIAN WATERMILFOIL (MYRIOPHYLLUM SPICATUM)

Eurasian watermilfoil (“milfoil,” EWM), a native to Asia, Africa and Europe, was introduced toNorth America between the 1880s and 1940, and spread to nearly every state and three southernCanada provinces It has displaced native milfoils and other submersed species, in part because itforms 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 humanactivities Seeds are formed in spike-like flowers extending above the water surface, but the primaryreproduction method is vegetative (Creed, 1998; Johnson and Blossey, 2002) This exotic, perhapsmore 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 beensatisfactory, in part because plants re-grow rapidly or harvesters spread fragments to uninfestedlake areas Grass carp (see later sections) do not prefer them Sudden, unexplained declines inheavily infested lakes suggested that biological agents, including insects, could be responsible.While searches for biocontrol organisms in milfoil’s native range (for classical biocontrol) havenot been successful, native and naturalized insects in North America that consume milfoil wereinvestigated for their potential to provide augmentive control However, there can be problems withaugmentive control, including: (1) native insect populations may not remain at the high densitiesneeded (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 isexpensive (Creed and Sheldon, 1995)

To be an effective augmentive biocontrol agent, the insect must be nearly monophagous on theexotic plant Otherwise, the insect may prefer and disperse to non-target plants it evolved with Ifthe exotic plant was not controlled by native insects when it invaded, then use of these insects foraugmentive 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 recentlaboratory 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.

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.)

5 Proportion ofweevil’s found Proportion of moths found

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 isformed, 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 compoundleads 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 butselect 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, andeventually mining the stem and destroying vascular tissue Larvae move about 0.5 to 1.0 m fromthe 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 larvaemay also create optimum conditions for fungal and bacterial infections of the plant Normally therecan 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 theweevil 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 betweenexotic 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/m2, about two adults, larvae,eggs or pupae/stem (Creed and Sheldon, 1995; Newman and Biesboer, 2000)

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 larvalpredators (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 successfuloverwintering Lawns manicured to the lake’s edge are unlikely to provide suitable overwinteringsites, 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 onwhich species can be easily cultured At this time, only the weevil is being cultured for controlpurposes 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 widespreadaugmentations 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 targetplants Severe infestations can be reduced with insects, and when used with herbicides in a waythat preserves an insect “reservoir,” there can be longer-term control What other native insectscould be used for aquatic plant control? Basic lake ecological research must continue

17.6 GRASS CARP

17.6.1 HISTORY 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 plantcontrol 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 ExperimentalStation 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 opensystem 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 wereintroduced without rigorous preliminary studies under quarantine It should have been predictedthat this “generalist” herbivore would have many negative features It is likely that grass carpimportation to the U.S would not receive authorization by the U.S Department of Agriculture ifpermission had been requested in more recent times A scientific effort to understand the beneficialand harmful effects was launched after their broadcast to the waters of North America, a classicexample of the “stock and see” mentality (Bain, 1993) so common with importation of exotic plantsand animals There have been many concerns about impacts on aquatic habitats where plants aredesirable, 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 areunder investigation in some provinces

Grass carp are popular, largely because they can provide low cost, long-term plant control, withacceptable negative impacts for some lake users For example, a lake can become completely

accessible for boating and swimming, though this may be at the expense of many lake and lakeshore species, and an increase in trophic state.

The purpose of this section is to provide lake managers with the information to make informeddecisions 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 ofmany 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 highconsumption 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 ofobtaining 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 Anenergy 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 (Leslieand Hestand, 1992) Triploid fish have a consumption rate that is about 90% of diploid fish Averagegrowth 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

Muoneke, 1992) Common adult weights exceed 9–10 kg, and 30–40 kg fish occur in Florida(Leslie and Hestand, 1992).

Grass carp exhibit feeding preferences, varying somewhat among U.S regions This fact hasimportant implications for stocking rates (see later section) Table 17.3, modified from Cooke andKennedy (1989), is a feeding preference list for triploid grass carp in Florida, Illinois, and Oregon-Washington Other state and regional preference lists are available (Florida, Colorado, California,Pacific Northwest United States, and New Zealand) (Chapman and Coffey, 1971; Swanson andBergerson, 1988; Pine and Anderson, 1991; Leslie and Hestand, 1992)

Eurasian watermilfoil (Myriophyllum spicatum) is not a preferred food plant It has a high

protein and gross energy content, but the lower stem is tough and fibrous, leading to rejection bythe fish Only when the more tender upper, new growth can be reached will grass carp eat thisplant (Pine et al., 1989), suggesting that accessibility and ease of mastication may be more importantthan nutritional quality in determining grass carp preferences Control of milfoil may be deferreduntil stocked fish are larger and preferred (often native) plants have been eliminated

Regional differences in food preferences have management implications Ceratophyllum

dem-ersum is a preferred plant in Florida, variably eaten in Oregon-Washington, but not eaten by Illinois

grass carp (Table 17.3) Triploid grass carp also rejected C demersum during experiments in

northern California (Pine and Anderson, 1991) The question remains whether palatability variesfrom region to region, whether there is a genetic basis to grass carp feeding behavior, or whetherfurther studies will demonstrate that these geographical differences are due to experimental design.One approach is to test palatability of nuisance plants for each water body prior to stocking(Chapman and Coffey, 1971; Bonar et al., 1987) Major nuisance exotic species, including waterhyacinth and alligatorweed, are not eaten or are non-preferred Additional research is needed aboutgrass carp feeding preferences

Feeding preferences mean that grass carp may allow non-preferred plants to become abundant,particularly when fish are under-stocked or when fish escape or die At low fish density, onlypalatable species are consumed (e.g., Fowler and Robson, 1978; Fowler, 1985) For example, inDeer Point Lake, Florida (Van Dyke et al., 1984; Leslie et al., 1987; J.M Van Dyke, FloridaDepartment of Natural Resources, personal communication), a large reservoir stocked in 1975–1978

(see case history), M spicatum became a problem after a native plant (Potamogeton illinoiensis)

was eliminated and grass carp density declined from escape and death In some lakes, grass carpfeed on detritus and animals after plant eradication (Edwards, 1973)

Plant preference rankings (e.g., Table 17.3) may be an oversimplification of the palatability

problem Consumption rates of Egeria densa and Elodea canadensis, taken from Pacific Northwest

lakes with varying chemical content, were significantly correlated with lake-to-lake variations inplant tissue composition Feeding rates were positively correlated with calcium content and nega-tively correlated with cellulose (Bonar et al., 1990)

17.6.3 REPRODUCTION OF GRASS CARP

An issue with grass carp is whether they will escape from a stocked lake, reproduce, and invadenon-target habitats where vegetation is desirable The criteria for successful reproduction arestringent (Stanley et al., 1978; Chilton and Muoneke, 1992), and it was assumed by importers thatreproduction would be unlikely outside the native range Spawning occurs in rivers, and is elicited

by a sharp rise in water level and by temperatures above 17°C The eggs must remain in suspension,

and it was assumed that currents of about 0.6 m/s were needed However, Leslie et al (1982) foundthat a velocity of only 0.23 m/s was sufficient to transport eggs in a Florida river Thus, in a warmFlorida river at this or greater current velocity, only 28 km would be required for incubation andhatching of eggs, a much shorter distance than previously reported Stream length required forhatching of eggs increases with decreasing temperature Larvae develop in quiescent areas (oxbows,sloughs) where they feed on zooplankton

Ceratophyllum demersum (coontail)

Eleocharis acicularis (needle rush)

Pontederia lanceolata (pickerelweed)

Wolffiella spp (bog mat)

Wolffia spp (watermeal)

Typha spp (cattail)

Azolla spp (azolla)

Spirodela (duckweed)

Variable Preference — May Eat

Myriophyllum spicatum (EWM) Potamogeton crispus (curly-leafed

pondweed)

Myriophyllum spicatum (Eurasian

watermilfoil)

smartweed)

milfoil)

Fuirena spp (umbrellagrass)

Nymphaea spp.(water lilies)

Variable Preference — May Eat

Brasenia schreberi (watershield)

Hydrocotyl spp (pennywort)

Panicum repens (torpedograss)

Stratiotes aloides (water aloe)

Non-preferred — Does Not Eat

Nuphar luteum (spatterdock) Ceratophyllum demersum (coontail) Potamogeton natans (floating leaf

Despite the assumption that reproduction would not occur outside the native range, therehave been many instances — in areas of diverse topography and latitude, ranging from the formerUSSR to Japan, Taiwan, the Philippines, and Mexico — where introduced grass carp havespawned successfully (Stanley et al., 1978) There is direct evidence that grass carp havereproduced in the Missouri, Mississippi, Lower Trinity (Texas), and Atachafalaya (Florida)Rivers, and in their tributaries and adjoining bays (Connor et al., 1980, Brown and Coon, 1991;M.A Webb et al., 1994; Raibley et al., 1995) It is unknown if grass carp populations willdisperse, but they do spawn in smaller river systems and farther north than previously documented(Brown and Coon, 1991) Because many escaped fish are diploids, wild grass carp populationsmay expand in distribution, with unknown impacts The continued sale and use of diploid fish

in North America should cease

Sterile grass carp were developed to solve the reproduction problem Early attempts to usesterile fish involved hybrids, but these had lower feeding efficiencies and fertile diploids couldoccur A solution involved the production of pure (unhybridized) triploid (three members of eachchromosome in cells) fish, using hydrostatic pressure or high temperature techniques that producenearly 100% triploids (Cassani and Caton, 1986)

No known procedure produces 100% triploidy consistently, and diploids and triploids cannot

be accurately separated by sight Fish producers must verify that fish sold are triploid One technique

is to examine a blood sample with a Coulter Counter with a channelizer Triploid red blood cellsare larger than those in diploids, and are verified with the Counter Three workers can examine

2000 to 3000 fish/day, with 100% accuracy Triploids are functionally sterile, with a very lowprobability of being a source of reproducing diploids (Allen et al., 1986; Allen and Wattendorf,1987) The production and verification of 100% sterile fish prompted several states to permit stocking(Table 17.2)

Alternanthera philoxeroides

(alligatorweed)

Nymphoides spp (floating heart)

Pistia stratiotes (waterlettuce)

Phragmites spp (reed)

Carex spp (sedge)

Scripus spp (bulrush)

Ludwigia octovalis (water primrose)

Colocasia esculentum (elephant-ear)

a Diploid carp.

Sources: Data based on Hestand, R.S and C.C Carter 1978 J Aquatic Plant Manage 16; Osborne, J.A 1978 Final

Report to Florida Department of Natural Resources University of Central Florida, Orlando; Nall, L.E and J.D Schardt.

1980; Van Dyke, J.M et al 1984 J Aquatic Plant Manage 22; Miller, A.C and J.L Decell 1984; Sutton, D.L and V.V.

Van Diver 1986 Grass Carp: A Fish for Biological Management of Hydrilla and Other Aquatic Weeds in Florida Bull.

867 Florida Agric Exper Sta., University of Florida, Gainesville; Bowers, K.L et al 1987 In: G.B Pauley and G.L.

Thomas (Eds.), An Evaluation of the Impact of Triploid Grass Carp (Ctenopharyngodon idella) on Lakes in the

Pacific Northwest Washington Cooperative Fisheries Unit, University of Washington, Seattle; Leslie, A.J., Jr et al 1987.

Unpublished Report; Pauley, G.B et al 1994; Van Dyke, J.M 1994; Murphy, J.E et al 2002 Ecotoxicolgy 11.

For example, the Illinois stocking model (Wiley et al., 1987) requires the following data: lakearea, percent of area less than 2.4 m (8 ft) in depth, percent of area heavily vegetated at peakbiomass, specific identity of dominant plants (adjusts for feeding preferences), and the climaticregion (adjusts for water temperature and length of growing season) The model assumes fish 25

cm (10 in.) in length will be stocked in the spring season, and considers whether all fish will bestocked at once (batch stocking) or whether serial stocking will be used (e.g., fish added every 5years) as long as control is desired The latter strategy uses fewer fish

The Illinois model emphasizes an attempt to maintain 40% plant coverage in littoral areas afterstocking, an amount optimal for largemouth bass in that state (Wiley et al., 1984), although optimalcoverage apparently varies from region to region For example, in 56 Florida lakes, ranging greatly

in area, depth, trophic state, and macrophyte abundance, adult largemouth bass density was notrelated to macrophyte abundance, but was positively correlated with trophic state Younger bassdensity was weakly correlated with macrophyte abundance (Hoyer and Canfield, 1996a, b) But,when submersed vegetation fell below 20% of total lake coverage in 30 Texas reservoirs, bassstanding crop and recruitment decreased (Durocher et al., 1984)

Figure 17.3 illustrates the application of the Illinois model to three plant communities, dominated

respectively by unpalatable (milfoil), palatable (pond-weed) and very palatable (Chara) plant

spe-cies The figure compares stocking recommendations with the fixed stocking rate, showing thatwith the fixed rate, the number of fish will be too high when littoral zone coverage is low andpalatable plants dominate, and too low when coverage is high and unpalatable plants are the nuisance.The significance of palatability and latitude in stocking rates is illustrated with the Illinois model.Consider a pond or lake near Chicago, Illinois (approx latitude 42°N) If the lake is dominated by

palatable species like Chara and naiads, the stocking rate would be 40 25-cm fish/ha followed in

6 years with a second stocking of 30/ha However, if this had been a milfoil-dominated lake, thestocking rate would be 170/ha followed by 69/ha 7 years later An identical pair of lakes in southernIllinois (approximately latitude 36°N) would have an initial stocking of 20/ha, followed by another

20 fish/ha in 5 years for the lake with palatable plants, and 151 fish/ha followed by 79/ha 7 yearslater for the lake with unpalatable plants (Wiley et al., 1987)

Fish size is important Stocking of fingerlings may result in high mortality, possibly from basspredation Fish at least 25 cm (10 in.) in total length are recommended in northern latitudes and

at least 30 cm (12 in.) in Florida (Shireman et al., 1978; Canfield et al., 1983)

Stocking to achieve an intermediate density of plants, while ideal, is difficult in practice Whilethere are cases of partial plant control (e.g., Lake Conway, Florida; Miller and King, 1984), theymay be the exception (Bauer and Willis, 1990; Hanlon et al., 2000) Stocking rates for an optimal

plant density are difficult to calculate due to variable rates of plant re-growth, water temperature,fish growth, and fish mortality (or escape) (Mitchell, 1980) Eradication of plants or failure tocontrol them are the usual outcomes of attempts to obtain intermediate plant biomass (Bonar etal., 2001).

An integrated control approach, utilizing low stocking densities, combined with initial chemical

or mechanical control, may circumvent the ecologically disruptive use of high densities followed

by plant eradication (Shireman and Maceina, 1981; Shireman et al., 1983) This strategy is difficultfor two reasons First, some lake users are dissatisfied if plant control is not rapid and complete

In Washington state lakes, for example, grass carp took 2 years or more to produce effects (Bonar

et al., 2001), leading lake users to add more carp which produced an overstocking The integratedapproach requires patience and still may lead to plant eradication (Shireman et al., 1983) Secondly,

FIGURE 17.3 A comparison of fixed rate (10 fish per acre) recommendations with recommendations from

the Illinois Stocking Model for three categories of plant palatability Each comparison shows rate for northernIllinois when littoral zones are 50, 70, and100% vegetated Graphs give stocking rate, in number of 10-in,fish, as a function of percentage of lake in littoral zone (From Wiley, M.J et al 1987 Controlling AquaticVegetation with Triploid Grass Carp Circular 57 Illinois Natural History Survey, Champaign.)

Palatable Plant Species

Percent littoral zone

herbicide-treated plants (e.g., diquat and fluridone) may have lower palatability to grass carp becauseresidues can persist (Kracko and Noble, 1993) This can lead to slower plant control, especiallywhen lower grass carp densities are used.

Containment is an important part of stocking Most states require an escapement barrier at thelake’s outlet and grass carp should not be added to a lake or impoundment unless an adequatebarrier is in place As demonstrated at Deer Point Lake, Florida (Leslie et al., 1987; J.M Van Dyke,Florida Department of Natural Resources, personal communication), containment is essential tomaintaining enough grass carp to bring about plant control (see case history) In reality, barriersare costly, and may impede water outflow if blocked with debris Grass carp also jump over barriers.Therefore, escape is common and the fish become pollutants

Once stocked with grass carp, lake users are committed There is no effective method ofselectively removing them, and plant control may persist for 15 or more years Fish ManagementBait, a rotenone-laced pellet (Prentiss Inc, Floral Park, New York, 11001), has some potential forgrass carp removal (Mallison et al., 1995) Bonar et al (1993) investigated several methods Earlierwork showed that fyke, gill, and trammel nets, and electroshocking, were ineffective Grass carp

could be lured to traps with lettuce (Latuca sativa) when submersed plants had been eradicated or

the lake had non-preferred plants Other baits (e.g., bread, cabbage, spinach, alfalfa, soybeans) werefar less effective Angling, using lettuce tied to a #8 hook with > 9 kg test line, was somewhatsuccessful (0.0–0.14 fish/man hour) in calm weather where attractant lettuce bundles were notblown away and the lake was devoid of submersed plants Other angling baits (e.g., doughballs,bread, catfish power bait, crappie jigs) were unsuccessful An effective technique (0.17–0.56fish/man hour) was herding fish into nets Angling and herding would be ineffective in large, deeperlakes The most effective options involve lake draining (with a high escape barrier) or application

of rotenone All fish should be eliminated, and this may have other beneficial effects for the lake(Chapter 9)

Grass carp cannot be stocked into one area of the lake with the expectation that they will remainthere Unlike harvesting and herbicide treatments, grass carp choose where and when to feed unlessbarriers to movement are used, as demonstrated in Lake Seminole, Georgia where grass carp wereprevented from leaving a 365 ha embayment Non-electrified barriers were ineffective, but anelectrified one prevented escape from the bay, demonstrating that it is possible to treat a selectedarea Cost of the barrier was $72,000 (Maceina et al., 1999)

17.6.5 CASE HISTORIES

17.6.5.1 Deer Point Lake, Florida

Deer Point Lake, a 1900-ha reservoir built in 1961, is the water supply for Panama City, and a

recreational area By 1975, Potamogeton illinoiensis and milfoil covered large areas, interfering

with lake use and drinking water intakes The previous edition of this text (Cooke et al., 1993)stated that pesticides were used on Deer Point Lake from 1972 to 1975 That statement was incorrect.Instead, grass carp were stocked in 1975 into fenced-off, predator-free grow-out areas at 43 fish/ha

of lake area The fish were released to the open lake in 1976 Additional grass carp were addedbetween 1976 and 1978, bringing stocking density to 61/ha by 1978 (Van Dyke et al., 1984; VanDyke, 1994)

P illinoiensis, a preferred plant by grass carp, was selectively grazed and eliminated by

1977–1978 Milfoil, a non-preferred plant, remained abundant until 1979, then declined In 1981,milfoil increased again, although native and preferred plants remained scarce (Figures 17.4 and

17.5) In 1985, there was a new stocking (21/ha) that maintained plant control until 1993, when

non-preferred native plants (Bacopa caroliniana, Vallisneria americana) increased, providing new waterfowl and fish habitat When preferred native species (e.g., Najas guadalupensis, Nitella spp.)

began to increase, lake managers concluded that the lake could be susceptible to the expanding