Biological control of melaleuca trees shows promise

LIKE ALL NATURAL ECOSYSTEMS, Florida's native habitats have developed a complex system of checks and balances that prevents the overpopulation of plant and animal species and maintains a healthy natural environment. Every native plant in Florida has evolved with a specific recipe of natural controls that includes environmental restraints such as water levels, as well as natural enemies including herbivores and pathogens. Natural controls regulate the native plant population.

When a non-native plant is introduced into a Florida habitat, it may have competitive advantages over indigenous plant populations because the natural controls that regulate the introduced plant in its native range may not exist in Florida.

As a result, the non-native plant often flourishes and out-competes Florida's naturally controlled native plants. The introduced plant may replace native species, clog waterways, degrade water quality, and impede recreation and navigation.

ONE WAY TO MANAGE INVADING NON-NATIVE PLANTS in Florida's watery systems is to use biological control agents such as insects, fish and pathogens.

Biological control is the purposeful introduction of natural enemies by scientists and environment managers as a means to weaken and suppress invading plants. biological control agents are used to decrease the invasive plants' competitive advantages over native species, and to weaken the invading population by increasing leaf mortality, decreasing plant size, reducing flower and seed production, and/or limiting population expansion.

For more than forty years, workers have introduced non-native biological controls to combat non-native invading plant populations in Florida. Thirteen biological control agents have been studied and then released since the 1960s. Jump down to the list.

• Discovery and identification: Scientists travel around the world in search of the target plant's natural enemies inside the plant's native range. Such field exploration, observation and preliminary testing takes years to complete.

• Approval for importation and study: When an organism is determined to be host specific (attacking only specific plants) in its native range, it is reviewed by the United States Department of Agriculture Technical Advisory Group before it is imported to the U.S. for further study.

  Hydrilla tuber weevils released during drawdown (1980s)

• Quarantine studies: Once approval is obtained, the potential biological control agent is imported to the U.S. and placed within a secured quarantine laboratory. There, the organism is raised and extensively studied for host-specificity using appropriate plant species, including related species in other states. Feeding trials and life-history experiments are meant to ensure that the organism will affect only the targeted invading plant species and will not impact native or crop species. This testing often takes another several years.

  In 2003, a new state-of-the-art biological control quarantine and rearing facility, was constructed in Ft. Pierce to replace small and outdated facilities Florida.

• Initial field release: If the biological control agent is proven to be host specific in quarantine and is capable of damaging the pest plant's growth or reproduction, it is released in specific areas. In the field, the biological control agent attacks the target plants; subsequent generations of the introduced organism suppress the invading pest plants over a long period of time.

• Monitoring: Of course, from the moment they are imported for quarantine study, all introduced biological control agents are tracked by state and federal scientists. As field data indicate, more and more releases of the organism may occur. Releases and results are annually recorded on U.S.D.A. Form AD 914.

However, the long-term benefits of an effective biological control agent can far exceed the development costs. The results from a successful biological control agent last longer than most management techniques and it reduces the need for, or amount of, herbicidal, mechanical, and physical controls. It is believed that successful biological controls save much time and money in aquatic and wetland plant management. During the past 40 years, thirteen biological controls have been evaluated overseas, studied in quarantine, and released in Florida and throughout the southeast U.S. to control five invasive aquatic plant species:

alligator weed	hydrilla	water hyacinth	water lettuce	melaleuca

Alligator weed (Alternanthera philoxeroides): Three South American insects were released in the 1960's to control alligator weed, one of the most prolific invasive aquatic plants infesting >80% of Florida's public waters. Although alone, each of these insects stress alligator weed, collectively, this suite of biological control agents have had devastating results on this once invasive aquatic plant. Alligator weed is still present in more than 80% of Florida public water, but at such low levels that it is rarely necessary to control with other means.

Alligator weed flea beetles (Agasicles hygrophila) were imported from Argentina and first released in Florida in 1964; an example of classical biological control. A member of the Chrysomelidae family, the insect consumes the leaves and parts of the stems of the aquatic form of alligator weed. The most effective of the three biological control insects used to control alligator weed, the U.S. Army Corps of Engineers cancelled all herbicidal spraying against alligator weed three years after its introduction. Still, the beetle is less effective in southern Florida because of its sensitivity to climatic extremes.

Alligator weed thrips (Amynothrips andersoni) is native to Argentina and was first released in 1967. It is the least known of the alligator weed biological control insects. Leaf damage by the thrips affects the plant by stunting its growth. This insect is the only one of the three that successfully controls the terrestrial form of alligator weed.

Alligator weed stem borer (Arcola (=Vogtia) malloi) is a small brown moth from Argentina that was released in 1971. The larvae mine the inside of the stem and cause the plant to wilt and die. This insect is capable of migrating great distances and is the most cold tolerant of the alligator weed insects. Control is most effective when used in conjunction with the Alligator weed flea beetle.

For more information on alligator weed and biological control, visit our page on this web site.

Brazilian pepper tree (Schinus terebinthifolius) : This species is a native of Argentina, Paraguay and Brazil. It is thought to have been introduced into Florida by 1842-1849 as a cultivated ornamental plant. Schinus is the Greek word for mastic-tree, a plant with resinous sap, which this genus resembles. The species name terebinthifolius is a combination of the genus name Terebinthus and the Latin name folia, leaf. It refers to the leaves of this plant which resemble those of species in the genus Terebinthus (Hall, Vandivir, Sellers & Langeland 1991, 2006).

1.1. Adventive biological control. The only insect currently causing some damage to Brazilian peppertree in Florida is the adventive torymid wasp, the Brazilian Peppertree Seed Wasp (Megastigmus transvaalensis) Hussey (Hymenoptera: Torymidae) , which attacks the drupes or seeds (Habeck et al. 1989, Wheeler et al. 2001, Cuda et al. 2002a). In recent years, this insect has been expanding its range throughout the Brazilian peppertree infested area (Wheeler et al. 2001, Cuda et al. 2002a). Megastigmus transvaalensis was originally described from South Africa (Boucek 1978), and was probably introduced accidentally into the USA from Reunion or Mauritius via France in Brazilian peppertree seeds sold as spices in some food shops (Habeck et al. 1989). Recently, Wheeler et al. (2001) completed a detailed study on the distribution and effect of the drupe-feeding wasp M. transvaalensis on Brazilian peppertree in Florida. During this 2-year study, they observed that up to 31% of the drupes were damaged by the wasp during the major winter fruiting period and up to 76% during the minor spring fruiting phase.

 

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Hydrilla (Hydrilla verticillata): Worldwide surveys began in 1981 to search for an effective biological control agent for the underwater plant, hydrilla. Some of the earliest research for the biological control of hydrilla was with snails and pathogens and they produced unsatisfactory results. As of now, four insects and one fish have been released to control hydrilla, but only two of these insects are established, and only one is commonly associated with hydrilla in the southeastern U.S. None of the insects have been able to adequately control or stress rapidly increasing hydrilla populations, but the fish has proven to be very effective. During the past 35 years the DEP has spent nearly $7.5 million -- more than half of its research budget -- to evaluate potential biological control candidates and release promising candidates that have passed quarantine regulations. This includes "in-house" research as well as collaborations with the University of Florida, US Army Corps of Engineers, and the USDA.

The DEP continues to fund overseas exploration for hydrilla bio-control agents. Much of this research is conducted in cooperation with various research entities to evaluate the overall effectiveness of the plant pathogen Micoleptodiscus terrestris in conjunction with herbicides to improve overall efficiency, especially for the control of some fluridone-resistant strains of hydrilla.

Hydrilla tuber weevil (Bagous affinis) was discovered in India and Pakistan and was released in the U.S. in 1987. The adult lays eggs on rotting wood and organic matter. After hatching, the larvae burrow into the ground until they find hydrilla tubers. The tuber is destroyed as the insects feed on it. Hydrilla tuber weevils are specific to hydrilla and therefore do not pose a threat to other aquatic plants. It was first released in in 1987 but failed to establish since they are only effective during draw downs and Florida lakes are rarely dry.

Asian hydrilla leaf mining fly (Hydrellia pakistanae) was located in India and first released in 1987. The larvae of the Asian hydrilla leaf mining fly and the following species burrow inside the plant and each insect destroys up to 12 leaves throughout the developmental period. However, the plant has not been effectively controlled by these established insects. Research efforts are underway to mass-rear the flies to use them in an inundative biological control strategy.

Australian hydrilla leaf mining fly (Hydrellia balciunasi) was found in Australia and first released in the U.S. in 1988. It has failed to establish in Florida waters.

Hydrilla stem borer (Bagous hydrillae) was imported from Australia and released in 1991. The larvae burrow into the submerged stems of hydrilla causing them to fragment. This control has been ineffective since it needs sandy shoreline for larvae to develop within stem fragments - a rare situation in Florida waters.

Hydrilla tip mining midge (Cricotopus lebetis)has a mosquito-like appearance, yet it does not bite. In 1992, USDA discovered that the midge larvae was attacking a mass of hydrilla in the Crystal River and causing significant damage. The larvae attack the apical meristem and stunt hydrilla growth by preventing the plant from reaching the surface of the water. This type of damage is desirable because it may prevent hydrilla problems related to navigation, water chemistry, and biodiversity. This insect is under evaluation for further use in other hydrilla infested spring runs.

Chinese grass carp (Ctenopharyngodon idella), a fish from China, is one of the most effective biological control agents for hydrilla and a number of other aquatic plants. The voracious herbivore prefers hydrilla and 2-25 fish can completely control one acre of hydrilla. Unfortunately, it is not a selective eater and the fish will also devour most submersed as well as emersed aquatic vegetation once the preferred hydrilla is depleted. Florida's interconnected surface waterways also make it nearly impossible to restrict its range. Because of the potential environmental damage caused by a breeding population of grass carp, possession of the fish is illegal. However, a genetically engineered "triploid" grass carp is sterile, and is now legal in Florida through a permit from the Florida Fish and Wildlife Conservation Commission (FFWCC). An efficient means of recapturing grass carp has not yet been developed and this limits the feasibility of employing the fish as a biological control agent. Triploid grass carp are stocked at very low rates (1-2 fish/acre) to control hydrilla in about 70 small Florida public waters (less than 500 acres in size and relatively self-contained). For more detailed information about the use of grass carp, go to this page of this web site.

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Water hyacinth (Eichhornia crassipes): Three biological control insects have been imported, studied, and released to control invasive water hyacinth, a floating macrophyte that was introduced to the U.S. during the New Orleans Cotton Exposition in 1884. It has been found that working together, these insects stress water hyacinth, reducing its' size and vigor, and reduce flower and seed production; however, by themselves they are not able to control water hyacinth.

Mottled water hyacinth weevil (Neochetina eichhorniae) was first released in 1972. The adults feed on the leaves and petioles, where they produce characteristic feeding scars. The larvae tunnel in the petioles and crown of the plant. It has been the most effective biological control insect for water hyacinth. This insect is able to stress plants, reduce flowers and seeds and reduce plant vigor.

Chevroned water hyacinth weevil (Neochetina bruchi) is very similar to N. eichhorniae and was first released in 1974. Both weevils reduce vigor and seed production and are devastating to young water hyacinth stands. Studies have shown a substantial decrease in plant growth when used in conjunction with herbicidal management. The weevils are unable to effectively control plants growing in water bodies with high nutrient loads.

Argentine water hyacinth moth (Niphograpta (=Sameodes) albiguttalis) was first released in 1977. The larvae feed by tunneling into the petioles of the younger, bulbous form of water hyacinth. It is less successful because it disperses rapidly, has patchy distribution, and may be completely excluded by the weevils on the older, non-bulbous plants.

Water hyacinth mite (Orthogalumna terebrantis) is an arachnid that is native to the U.S. In high numbers, the mites can dessicate hyacinth foliage and casue the leaves to turn brown. Severe damage may occur in small areas, but rarely enough to successfully control water hyacinth populations.

For more information on water hyacinth and biological control, visit our page on this web site.

WATER HYACINTH BIOLOGICAL CONTROL

weevil damage	weevil in action	yet more damage

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Water lettuce (Pistia stratiotes): Two South American insects have been released in Florida to combat water lettuce. Only one of these insects is established, but it has not been able to adequately control or stress the plant populations in most situations.

Water lettuce leaf weevil (Neohydronomous affinis) was imported from South America after showing promising results as a biological control agent in Australia and South Africa. It was imported to the U.S. in 1986 and 1988. Two years after its release the weevil population increased and effectively suppressed water lettuce in several sites. It is now established and distributed widely throughout the state, but rarely suppresses water lettuce growth.

Water lettuce leaf moth (Spodoptera pectinicornis) is native to Southeast Asia and was imported from Thailand. The caterpillar was first released in Florida in 1990, but failed to establish. It its native range, augmentive releases of the moth have been used to successfully control water lettuce in rice paddies.

For more information on water lettuce and biological control, visit this page.

Melaleuca (Melaleuca quinquenervia): Two insects have been released in Florida to combat melaleuca, an invasive weedy tree intentionally imported from Australia in 1906. At least one of the biological control insects shows promise.

Melaleuca leaf weevil (Oxyops vitiosa) was imported from Australia in 1992 and released in 1997 to slow the spread of melaleuca. The insect feeds on the leaves, stems, and buds of the invading trees and interferes with normal plant processes such as seed production and plant growth. This biological control appears very promising.

Melaleuca defoliating saw fly (Lophyrotoma zonalis): (more on this) In 2002, two other species, the melaleuca psyllid (Boreioglycaspis melaleucae) and the melaleuca leaf blotching bug (Eucerocoris suspectus) are awaiting approval for shipment into quarantine.

For more information on melaleuca and biological control, visit; our page on this web site.

Other biological controls studied in the past include:

Snails (Marisa cornuariites) were found to feed on several species of aquatic plants. Three small lakes in southern Florida were stocked with 1,000 snails and were free of aquatic plants in 18 months.

Research, implementation, and results of biological controls are slow. Therefore, it is important to explore other control measures such as herbicidal, mechanical, and physical while establishing a successful biological control agent.

Please read here about steps you can take to help prevent invasive aquatic plant problems.

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For more information about biological control in Florida, visit:

Our other page on biological control

University of Florida, Department of Entomology and Nematology
web page on biological control

USDA web page on biological control

Animal and Plant Inspection Service page on biological control

Biological Control of Invasive Plants in the Eastern United States - An online book that provides a reference guide for field workers and land managers concerning the historical and current status of the biological control of invasive plant species in the eastern United States.

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The Creators

This page was authored by Sarah Cervone.
Data is from the APIRS database.
This page was designed by Sara Reinhart.
Photography and graphics are by Ann Murray, Sara Reinhart and Vic Ramey.

Karen Brown is the editor.

DEP review by Jeff Schardt and Jim Cuda.

Main Index

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This project is a collaboration of
the Center for Aquatic and Invasive Plants, University of Florida,
and the Bureau of Invasive Plant Management, Florida Department of Environmental Protection

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Copyright 2006 University of Florida