The use of insects to control aquatic weeds began with alligatorweed and was successful (Buckingham and Habeck 1990, Buckingham et a. 1983). Thus, other insects have been evaluated and released on several pest plant species such as hydrilla, waterhyacinth, and giant salvinia. Host-specific insects and plant pathogens have been released to increase leaf mortality, decrease plant size, and reduce population expansion. Herbicides are used for current management, however, insect control shows promise for long-term control (Schmitz et al. 1991). Charudattan and Browning (1992) and Charudattan (1990) discussed the special problems with the biological control of aquatic weeds.
Laing and Hamai (1976), Clausen (1978), Luck (1981), and Funasaki et al. (1988) tabulated the biological control agents that were introduced into various regions of the world. Denmark (1964) and Denmark and Porter (1973) had previously documented the introduction of biological control agents into Florida. Frank and McCoy (1993) expanded the scope of documentation and brought the records up-to-date. They determined that about 351 (a few species were lumped) insect species have been imported into Florida for potential release as biological control agents since 1890; many were never released. However, 151 were introduced as biological control agents of insect pests and weeds. Of the 351 taxa, 32 seem to have occurred already in Florida; 24 seemingly are natives and 8 seemingly are immigrants. Some of the immigrants, such as Bathyplectes curculionis (Thomson; Hymenoptera: Ichneumonidae), seem to have arrived in Florida by immigration from other states into which they had been imported, whereas others, such as Megastigmus transvaalensis (Hussey; Hymenoptera: Torymidae) and Utetes anastrephae (Viereck; Hymenoptera: Braconidae), may have arrived directly from abroad by stowing away in cargoes of plants and other materials (Frank & McCoy 1992). Another 11 taxa are thought to have been introduced (Frank and McCoy 1992) because permits were issued for their importation, but no actual records of importation could be located. Three of the released species are not biological control agents, leaving 151 taxa, consisting of 139 targeted insect pests and 12 targeted plant pests.
Biological control agents have been released in Florida since the 1890's (Frank and McCoy 1992). An estimated 24.5% of the released species for the control of insect pests and an estimated 66.7% for the control of weeds have established populations in Florida. The established proportion of insect predators (26.7%) was very similar to that of insect parasitoids (23.9%). Targeted insect pests were mainly Homoptera (48%), Lepidoptera (24%), and Coleoptera (10%). Most targeted insect pests (79%) and nuisance plants (75%) are not native to Florida; 43% of the insect pests are native to Asia, and 50% of the weeds are native to South America. None of the targeted native insect pests and weeds occurs only in Florida. No clear relations existed between the number of released individuals and their geographic origin, county in which they were released, and probability of establishment (Frank and McCoy 1993).
Almost all introduced insects that Frank and McCoy (1993) included in their tabulation were imported deliberately and deemed beneficial and suitable for release. However, Howarth (1991, 1992) questioned the certainty that a released insect does not harm that ranges from negligible to extinction of other species. Small changes that the organism causes can lead to large environmental problems that are completely unanticipated. Release of the biological control agents usually was subject to proof of host-specificity. All insects that were introduced into the United States for biological control require (1) a permit from the Animal and Plant Health Inspection Service, Plant Protection and Quarantine, of the U.S. Department of Agriculture, (2) a Declaration of Importation (for all live and dead specimens) from the U.S. Fish and Wildlife Service and (3) a permit from the Florida Department of Agricultural and Consumer Services for insects that are imported as biological control agents (personal communication from J.H. Frank, Entomology Department, University of Florida).
The cost of developing biological control agents is high and time-consuming and requires the investment of staff, other valuable resources, and--frequently--international cooperation. Few attempts to evaluate the total costs and benefits of control have been made (Djerassi et al. 1974). Schroeder and Goeden (1986) discussed the theory and practical considerations of the search for and evaluation and use of insects as biological control agents of introduced nuisance plants. Harris (1979) described the costs of the biological control of introduced nuisance plants with introduced insects in Canada. A model to calculate the expected net benefits from biological control was developed by Habeck et al. (1993).
Frank and McCoy (1993) included in their list of insects introduced into Florida since 1970 some unsolicited species that were shipped to the quarantine facility of the Florida Biological Control Laboratory by foreign suppliers and terminated in quarantine, some unexpected parasitoid species that emerged from their imported hosts in the quarantine facility, and two species that were imported by members of the public without permits and were released in Florida. They omitted from the list any imported pest species that were brought to the quarantine facility simply as a host for beneficial parasitoids or predators that were terminated in the quarantine facility, species that were imported by the pet trade or by members of the public without permits or other public record, species that were imported with permits for experimental purposes in secure laboratories, species that were imported with permits for educational purposes and not intended for release (such as exotic butterflies), and beneficial species that were imported with permits by commercial organizations as biological control agents for pests (Frank and McCoy 1993).
Since 1973, all insects that were purposely legally imported into the United States are tracked by the U.S. Department of Agriculture. This organization annually compiles a list of the insects imported and recorded on FORM AD 914.
J. H. Frank, Professor, Entomology Department, University of Florida, Gainesville, assisted us with the identification of all of the aquatic insects and insects that were imported to control aquatic or semi-aquatic nuisance plants (Frank and McCoy 1992 and 1993).
Toxorhynchites amboinensis (Doleschall). This insect, belonging to the Family Culicidae/Diperta, was imported from Indo-Malaysia via Louisiana and was released ca. 1986 and in subsequent years in Duval and St. Lucie counties, Florida, to control Aedes aegypti and other mosquitoes whose larvae inhabit artificial containers. It does not survive winters in Florida. (Frank and McCoy 1993). This species is not established at the present time.
Toxorhynchites splendens (Wiedemann). This insect, belonging to the Family Culicidae, was imported from Burma via Hawaii, Indiana, and Louisiana and was released in Florida in Bay County in 1986-1988, in Leon and Sarasota counties in 1990, in Palm Beach and Walton counties in 1991, and in Hillsborough County in 1992 to control Aedes aegypti and other mosquitoes the larvae of which inhabit artificial containers. It has not survived the winter at any of the localities where it was released (Frank and McCoy 1993).
Neohydronomus affinis Hustache. This small South American weevil, Family-Curculionidae, previously controlled waterlettuce in Australia and South Africa. It was originally tested and released in Australia, where profound control of waterlettuce at release sites was obtained within 18 months (Harley et al. 1984). It was imported into the United States from Brazil via Australia in 1986 and 1988 for the control of waterlettuce Pistia stratiotes and tested in quarantine in Gainesville, Florida, and released in April 1987 on a 30-ha waterlettuce infestation on Kraemer Island in Lake Okeechobee (Dray et al. 1990). By April 1989, the weevil population increased to extremely high densities and thoroughly suppressed the waterlettuce population. These results were repeated at other sites. The weevil was released in 1987-1988 in Broward, Palm Beach, and St. Lucie counties, Florida, and is now established and widely distributed in Florida (Frank and McCoy 1986, 1988; 1993; Thompson and Habeck 1989).
Spodoptera pectinicornis (Hampson). This moth, Family Noctuidae, previously identified as Namangana pectinicornis and as native to Southeast Asia, has been successfully used in Thailand where it was imported during 1986-1988 for the control of waterlettuce and released in 1990 in Glades, Palm Beach, and St. Lucie counties, and in 1991 in Brevard, Broward, Gadsden, Glades, Okeechobee, Putnam, and Sumter counties; it is not yet clear that establishment is permanent (Frank and McCoy 1986, 1987, 1988, 1993; Buckingham & Habeck 1990; Dray and Center 1992; D. H. Habeck, Professor, Entomology Department, University of Florida, Gainesville, personal communication). Center et al. (1991) considered it a potential, effective control agent. This species is still under study.
Three host-specific South American insects were found and eventually released as biological control agents of Alligatorweed (Alternanthera philoxeroides). These include the alligatorweed flea beetle (Agasicles hygrophila) that was released in 1964; the alligatorweed thrips (Amynothrips andersoni) that was released in 1967; and the alligatorweed stem borer (Vogtia malloi), a moth that was released in 1971 (Center et al. 1991).
Alligatorweed flea beetle (Agasicles hygrophila) Selman & Vogt. This flea beetle, family Chrysomelidae, was imported from Argentina. Lack of suitable chemical control for alligatorweed led to the consideration of biological control as a possible solution. This insect was identified as a possible control and was evaluated (Brown and Spencer 1973) and released in 1965-1972 to control alligatorweed in Alachua, Baker, Bradford, Broward, Calhoun, Citrus, Clay, Dixie, Duval, Escambia, Flagler, Glades, Hendry, Hillsborough, Marion, Palm Beach, Polk, Putnam, St. John's, St. Lucie, and Volusia counties where it is now established. It was released in 1979 in Alachua County (Zeiger 1967; Denmark and Porter 1973; Frank and McCoy 1974, 1993; Coulson 1977; Buckingham et al. 1983; Buckingham and 1990). This flea beetle was introduced to control alligatorweed by consuming leaves and portions of stems during the latter stages of an infestation (Buckingham and 1990). It is restricted by winter temperatures to Florida and to the coastal areas of other southern states, but beetles that are collected in the south and released in spring or early summer can provide control in northern areas (Cofrancesco 1984; Buckingham and 1990). The alligatorweed flea beetle is the most effective of the three insects that were introduced to control this pest. It is especially effective in coastal areas but less so farther inland (Center et al. 1991).
Alligatorweed stem borer (Vogtia malloi Pastrana). This moth, family Pyralidae,is native to Argentina and was released to control alligatorweed in 1971-1972 in Alachua, Broward, Duval, Orange, and St. Lucie counties, where it is established (Brown and Spencer 1973; Coulson 1977). Each summer, this moth flies northward in the Mississippi Valley from coastal sites and flies inland from South Carolina coasts. By mining the insides of the stems, the larvae cause the weed to wilt and die (Buckingham and 1990). The alligatorweed stem borer is a small, brown moth. Because of its high dispersive ability, this insect readily moves inland where it can become an important biosuppressant. Damage by the alligatorweed borer causes the stems to collapse and the mat to acquire a flattened appearance. This, in conjunction with defoliation by the flea beetle provides control (Center et al. 1991).
Alligatorweed Thrips (Amynothrips andersoni) O'Neill. This thrips, family Paleothripidae, is native to Argentina and was released for the control of alligatorweed in 1976-1972 in Alachua, Broward, Clay, Duval, Glades, Orange, and Palm Beach counties where it is now established (Coulson 1977; Buckingham and 1990). The alligatorweed thrips is the least well known of the three biological control agents of alligatorweed . They do not readily disperse, and they do not seem to severely impede alligatorweed growth. However, field evaluations of the effectiveness of the thrips have never been conducted (Center et al. 1991).
Eubrychius spp. This species, belonging to the family Curculionidae, is native to China and was imported in 1991 for the control of Eurasian watermilfoil (Myriophyllum spicatum). The culture was lost in quarantine (Frank and McCoy 1991, 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication).
Phytobius (Litodactylus) leucogaster (Marsham). This species, belonging to the family Curculionidae, was imported from California in 1978-1979 and was released for the control of Eurasian watermilfoil in 1979 in Levy County. It is probably not established (Frank and McCoy 1978, 1979, 1993; Buckingham and 1990; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication). This flower- and seed-eating weevil ranges across the northern United States to California (Buckingham and Bennett 1981).
Acentria ephemerella (Denis and Schiffermuller). This species belongs to the family Pyralidae and is native to the northern United States and was imported in 1975-1976 (under the name Acentropus niveus) and in 1978 to control Eurasian watermilfoil. The culture died in quarantine (Frank and McCoy 1975, 1976, 1978, 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication).
Parapoynx stratiotata L. This insect, belongs to the family Pyralidae, was imported from Italy via Delaware, from Yugoslavia, and from Italy in 1975-1976 by N. R. Spencer as a potential biocontrol agent of Eurasian watermilfoil. Research on it was terminated in quarantine (Frank and McCoy 1975, 1976, 1993; BIRL 1992; D. H. , Professor, Department of Entomology and Nematology, University of Florida, Gainesville, Florida, personal communication).
Worldwide surveys were begun in 1981 to find biological control agents for hydrilla (Hydrilla verticillata). Several species of insects were found. Two species from India and one from Australia were released. Other promising insects are known from different parts of the world but have not yet been evaluated. Two species of leaf-mining flies, Hydrellia pakistanae from India and an undescribed Hydrellia balciunasi from Australia, were released in Florida. The larva burrows and destroys as many as 12 leaves during its development. These flies have potential for control of hydrilla if they can be colonized in the field (Center et al. 1991).
Bagous affinis Hustache. This weevil, family Curculionidae, occurs naturally in India and Pakistan. It was imported in 1982-1983, 1986, and 1990-1991 for the control of hydrilla and released in 1987 in Lake Tohopekaliga, Osceola County. It was established temporarily (Frank and McCoy 1993; Buckingham 1988; Buckingham and 1990). This weevil is specific to hydrilla and attacks its tubers, also called subterranean turions, in dry water bodies. Its use will be limited primarily to drawn-down lakes or canals (Buckingham and 1990). Additional studies are needed to determine whether this weevil can control hydrilla tubers (Center et al. 1991). Bennett and Buckingham (1991) discussed the results of laboratory studies of this species.
Bagous dilgiri Vazirani. This weevil, family Curculionidae, was imported from India in 1983 for the control of hydrilla. It was terminated in quarantine (Bennett and Buckingham 1991; Frank and McCoy 1993) because the insect also developed on the native species Potamogeton spp. and Najas spp.
Bagous laevigatus O'Brien & Pajni. This weevil was imported from India in 1983 and in 1986 for the control of hydrilla. It was terminated in quarantine after host-range testing (Bennett and Buckingham 1991; Frank and McCoy 1993) because hydrilla was not its principal host plant.
Bagous vicinus Hustache. This weevil was imported from India in 1983 for the control of hydrilla. Research on it was terminated in quarantine (Bennett and Buckingham 1991; Frank and McCoy 1993) because this insect damaged only stems out of water.
Bagous hydrillae O'Brien. This weevil was imported from Australia in 1987, 1988, and 1991 for the control of hydrilla and was released in 1991 in Broward, Palm Beach and Sumter counties. Its establishment is still uncertain (Center 1992; Frank and McCoy 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication).
Polypedilum dewulfi Goetghebuer. This midge, family Chironomidae, was imported from Burundi in 1990 for the control of hydrilla (Frank and McCoy 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication), but it could not be colonized in quarantine.
Polypedilum wittae (Freeman). This midge was imported from Burundi in 1990 by G. R. Buckingham (Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication), but attempts to colonize it in quarantine were unsuccessful.
Hydrellia balciunasi Bock. This fly, belonging to the family Ephydridae, was imported from Australia in 1988, 1989, and 1991 for the control of hydrilla and was released in 1989 in Broward County, in 1990 in Broward County, and in 1991 in Broward, Collier, and Sumter counties. Its establishment is not certain (Buckingham and 1990; Center 1992; Frank and McCoy 1993). The results of the biological and host-range studies of this species were summarized by Buckingham and Okrah (1993).
Hydrellia pakistanae Deonier. This Indian leaf-mining fly, belonging to the family Ephydridae, has a native range including India, Pakistan, and China. It was imported in 1986 and 1990 for the control of hydrilla and released in 1987 in Polk and Marion counties, in 1988 in Broward, Glades and Palm Beach counties, in 1989 in Broward, Glades, Osceola, and Polk counties, and in 1990 in Broward, Glades, Jefferson, Lake, Okeechobee, Osceola, and Palm Beach counties where it is now established (Buckingham 1988; Buckingham and 1990; Center 1992; Frank and McCoy 1993). The results of the biological and host-range studies of this species were summarized by Buckingham and Okrah (1993). Its larvae consume the contents of hydrilla leaves that become transparent and eventually drop off (Buckingham and 1990).
Hydrellia sarahae Deonier. This fly was imported from India and China in 1990, 1991, and 1992 for the control of hydrilla. It has not yet been released (Frank and McCoy 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Florida, personal communication).
Parapoynx diminutalis Snellen. This small aquatic moth, family Pyralidae, from Southeast Asia was accidentally introduced, probably with imported aquarium plants. It is not widespread in the state and seems to be specific to hydrilla in the field. It occasionally causes heavy defoliation of hydrilla in Florida (Buckingham and 1990). Although little is known about it, the occurrence of this moth seems sporadic and unpredictable, and occurrences do not result in acceptable levels of control (Center et al. 1991). This species was imported from Asia via Panama in 1980-1982 for the control of hydrilla; however, the same species was already established elsewhere in Florida (Frank and McCoy 1993; G. R. Buckingham, Research Entomologist, Florida Biological Control Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainsville, Florida, personal communication).
Three species of insects have been released to control waterhyacinth (Eichhornia crassipes). The first was a weevil, Neochetina eichhorniae (family Curculionidae), was released in Florida in 1972. The second was Neochetina bruchi, another weevil that is quite similar to the first (Center 1982). It was released in Florida in 1974. The third insect was a moth, Sameodes albiguttalis (family Pyralidae), named the waterhyacinth borer, and was released in 1977 (Center 1984; Center et al. 1991). The weevils (especially N. eichhorniae) have been the most effective of the waterhyacinth insects. Outbreaks of waterhyacinth borers are devastating to young waterhyacinth stands and sometimes prevent regrowth after herbicidal control. Because plants are attacked only briefly during early mat development, however, waterhyacinth borer populations seem sporadic. During this limited period, they effectively slow the rate of mat development. Because the presence of waterhyacinth borers may not be detected if sites are not surveyed regularly, the importance of this insect is easily underestimated (Center et al. 1991). Waterhyacinth weevils and borers suppressed waterhyacinth growth in many areas. This control is sometimes manifested as sudden declines, which are however rare. Instead, long-term decline of the plant population typifies the normal biocontrol pattern (Center et al. 1991). Charudattan et al. (1978) discussed the effects of fungi and bacteria on the decline of arthropod-damaged waterhyacinth.
Neochetina bruchi Hustache. This beetle was imported from Argentina in 1974 for the control of waterhyacinth and was released in 1974. It was also imported in 1975 and released in Lee County (Perkins and Maddox 1976; Grissell 1978; Cassani et al. 1981; Center and Durden 1986; Haag 1986; Buckingham and 1990; Frank and McCoy 1993). It is established in Florida. During the development of this project, it was discovered that two species of weevils were involved: N. bruchi and a new species, N. eichhorniae (Warner). The discovery that there were two weevils on the hyacinth delayed the program because some tests had to be repeated to determine whether the results were caused by one or both species. Both species are seemingly host specific to E. crassipes (Perkins and Maddox 1976).
Neochetina eichhorniae Warner. This weevil was imported from Argentina. It has been also reported from Bolivia and Trinidad. A preliminary summation of the studies on the host specificity this species was prepared and submitted to the Working Group on Biological Control of Weeds for clearance of quarantine in the United States. The Working Group granted this request but recommended additional testing on several aquatic plant species before release into the United States. Initially the testing and studies, including work on the additional test plants were conducted in Argentina in 1968-1971 and in quarantine in the United States in 1971. After approval, it was released in 1972, in Broward County and in 1974 in Glades and Lee counties. It was also imported in 1975 (Perkins 1973; Cassani et al. 1981; Center and Durden 1986; Haag 1986; Frank and McCoy 1993).
These two weevils were credited with reducing waterhyacinth in Florida lakes. By scraping the leaf surface, the feeding adults reduce photosynthesis; the larvae mine down the petioles, increasing the overall amount of pathogens that can attack the plant (Buckingham and 1990).
Acigona infusella (Walker). This moth, belonging to the family Pyralidae, insect was imported from Argentina in 1974-1975 for the control of waterhyacinth but was not released and died in quarantine (Frank and McCoy 1993).
Sameodes albiguttalis Warren. This moth, family Pyralidae was imported from Argentina in 1975-1976 and released for the control of waterhyacinth in Broward, Collier, Dade, and Pinellas counties in 1977-1979 (numbers not counted) and in 1979-1980 in Alachua County (79,093 in 1979,and 19,764 in 1980). It was established by 1979 (Center and Durden 1981; Center 1984; Buckingham and 1990; Frank and McCoy 1993).
Orthogalumna terebrantis Wallwork, Oribatid mite. This mite seems to be a South American immigrant that was already present in Florida. It only occasionally causes severe damage to waterhyacinth in southern Florida and does not seem to be an important agent (Buckingham and 1990).
Cercospora rodmanii Conway. This seemingly native fungus was found during a survey of the pathogens of waterhyacinth in the Rodman Reservoir, Florida. Conway et al. (1978) discussed the development of this fungi as a biological control agent of waterhyacinth. Additional information on this species can be found under the section titled Biological Control Agents Other Than Insects. Charudattan (1984, 1986) discussed the role that this species might play in controlling waterhyacinth.
Oxyops vitiosa Pascoe. This weevil, family Curculionidae, was imported from Australia in May 1992 and was approved for a quarantine study in the United States by the U.S. Department of Agriculture Animal and Plant Health Inspection Service. It is now under study in Gainesville, Florida. Preliminary laboratory and greenhouse tests indicate that the insect is specific to melaleuca (Melaleuca quinquenervia; Leist 1993) and may be released in 1994. Whether this insect alone will be able to control the plant is doubtful.
Other pest plant species that will be considered for control by arthropods include limnophila (Limnophila sessiflora), hygrophila (Hygrophila polysperma), water morning glory (Ipomoea aquatica), and parrotfeather (Myriophyllum aquaticum; Buckingham and 1990; Center et al. 1991). None is native to the United States.
