12.3C: Exotic Species - Biology

12.3C:  Exotic Species - Biology

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Exotic species introduced into foreign ecosystems can threaten native species through competition for resources, predation, and disease.

Learning Objectives

  • Describe the impact of exotic and invasive species on native species

Key Points

  • Exotic species introduced to new environments often reset the ecological conditions in that new habitat, threatening the species that exist there; this is the reason that they are also termed invasive species.
  • Invasive species that are closely related to rare native species have the potential to hybridize with the native species; harmful effects of hybridization have led to a decline and even extinction of native species.
  • Biologists studying frogs and toads may be inadvertently responsible for the worldwide spread of a fungus deadly to amphibians.

Key Terms

  • invasive species: any species that has been introduced to an environment where it is not native and has since become a nuisance through rapid spread and increase in numbers, often to the detriment of native species

Exotic Species

Exotic species are those that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Such introductions probably occur frequently as natural phenomena. For example, Kudzu (Pueraria lobata), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States: up to one foot each day. It is now a pest species, covering over seven million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess preadaptations that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat, resetting the ecological conditions in the new environment, while threatening the species that exist there. For this reason, exotic species, also called invasive species, can threaten other species through competition for resources, predation, or disease.

Exotic Species Threaten Native Species

Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regimen, nutrient cycling, and hydrology in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass, Spartina alterniflora, threatens the existence of California cordgrass in San Francisco Bay. Invasive species cause competition for native species. Four hundred of the 958 endangered species under the Endangered Species Act are at risk due to this competition.

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis. There is evidence that the fungus, native to Africa, may have been spread throughout the world by transport of a commonly-used laboratory and pet species: the African clawed toad (Xenopus laevis). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana, which has also been widely introduced as a food animal, but which easily escapes captivity, survives most infections of Batrachochytriumdendrobatidis and can act as a reservoir for the disease.

Global trade in exotic pets 2006-2012

International trade in exotic pets is an important and increasing driver of biodiversity loss and often compromises the standards required for good animal welfare. We systematically reviewed the scientific and gray literature and used the United Nations Environment Programme - World Conservation Monitoring Centre (UNEP-WCMC) Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) trade database to establish temporal and geographical trade patterns of live exotic birds, mammals, and reptiles and to describe trends in research, taxonomic representation, and level of threat and legal protection of species traded. Birds were the most species-rich and abundant class reported in trade reptiles were second most abundant but unusually the most studied in this context and mammals were least abundant in trade. Mammalian and reptilian species traded as pets were more likely to be threatened than expected by random. There have been a substantial number of Appendix I listed captive-bred mammals and birds and wild-caught birds and reptiles reported in trade to CITES. We identified the Middle East's emerging role as a driver of demand for exotic pets of all taxa alongside the well-established and increasing role of South America and Southeast Asia in the market. Europe, North America, and the Middle East featured most heavily in trade reports to CITES, whereas trade involving South America and Southeast Asia were given most emphasis in the literature. For effective monitoring of and appropriate response to the international exotic pet trade, it is imperative that the reliability and detail of CITES trade reports improve and that scientific research be directed toward those taxa and locations that are most vulnerable.

Keywords: CITES animal welfare bienestar animal exotic pet trade mercado de mascotas exóticas mercado de vida silvestre wildlife trade.

12.3C: Exotic Species - Biology

When we compare what we know about cancer in humans, and even in dogs and cats, exotic animal veterinarians are often working in the dark. Our patients deserve better.

  • Research and collaboration is needed. Researchers and clinicians must unite to find the common causes of cancer across all species. This holistic view will help us better understand various cancer models and ways to treat both human and animal cancers.
  • Veterinary cancer therapy will only improve with advanced knowledge. The field of oncology for exotic species is really in its infancy. Basic cancer biology, treatment protocols, response to therapy, prognostic information and diagnostic planning are currently under-represented in cancer research.
  • Human research can b enefit fr om our species. Few people realize that many of the advances in human cancer research were made by studying cancer-causing viruses in other species. Many of the basic genetic alterations that cause cancer occur in genes that are highly conserved across a wide range of species.

A whole world of cancer biology awaits in companion exotic and zoological species. We can always accomplish more when we work together.


The presence of exotic species, by itself, not necessarily represent a problem. Imagine a field of potatoes or corn, which come form America and don’t suppose an environmental problem by themselves. In most of the cases, the problem is when they become invasive species, which represent a worldwide problem, especially in islands and archipelagos, for the impact that they suppose:

  • Alteration and degradation of habitat.
  • Biodiversity loss.
  • They can suppose a health problem.
  • They can suppose a negative impact on economy, for the negative effect on natural resources and on tourism.

Restoring Balance: Using Exotic Species to Control Invasive Exotic Species

Department of Entomology, University of California, Riverside, CA 92521, U.S.A., email [email protected]

Department of Entomology, University of California, Riverside, CA 92521, U.S.A., email [email protected]


Abstract: Invasive species threaten natural habitats worldwide, and active human management is required to prevent invasion, contain spread, or remediate ecosystems following habitat degradation. One powerful technology for invasive species management in sensitive habitats is biological control, the use of carefully selected upper-trophic-level organisms that utilize the exotic pest as a resource, thereby reducing it to less harmful densities. Many in the conservation biology community view this pest-management technology as a high-risk enterprise because of potential collateral damage to nontarget species. The potential benefits arising from successful biological programs are reduced pesticide use, significant pest suppression, and a return to ecological conditions similar to those observed before the arrival of the pest. Biological control as a pest-management strategy has limitations: some pest species may not be suitable targets for biological control because natural enemies may not be sufficiently host-specific and may pose a threat to nontarget organisms. In some instances, substantial effects on nontarget species have occurred because generalist natural enemies established as part of a biological control program heavily utilized other resources in addition to the target pest. To minimize nontarget impacts, regulations governing releases of natural enemies are becoming more stringent, as evidenced in New Zealand and Australia. Voluntary codes of good practice are being advocated by the Food and Agriculture Organization to promote wide adoption of safety measures, which, if followed, should result in the selection of agents with high levels of host and habitat fidelity. Biological control programs in support of conservation have traditionally targeted weed species that threaten natural areas. More recently, exotic arthropod pests that compete with native wildlife or damage native plants have become targets of conservation-oriented biological control programs. Extension of biological control to new targets of conservation importance, such as invasive aquatic invertebrates and pestiferous vertebrates, is warranted. In many instances, once prevention, containment, and eradication options have been exhausted or deemed infeasible, carefully orchestrated biological control programs against appropriately selected targets may be the only feasible way to control invasive species affecting communities under assault from exotic species.


Resumen: Las especies invasoras amenazan los hábitats naturales en el mundo y se requiere de manejo humano para prevenir la invasión, contener la expansión o remediar ecosistemas después de la degradación de hábitats. El control biológico, el uso de organismos de niveles tróficos superiores cuidadosamente seleccionados que utilizan la especie exótica como recurso reduciéndola a densidades menos dañinas, es una poderosa tecnología para el manejo de especies invasoras en hábitats sensibles. Muchos en la comunidad de biólogos de la conservación consideran esta tecnología de manejo de plagas como de alto riesgo por el daño colateral potencial a otras especies. Los beneficios potenciales de programas biológicos exitosos son la reducción de usos de pesticidas y un regreso a condiciones ecológicas similares a las observadas antes de la llegada de la plaga. El control biológico como estrategia de manejo de plagas tiene limitaciones algunas especies de plagas pueden no ser blancos adecuados para el control biológico porque sus enemigos naturales pueden no ser lo suficientemente específicos y constituir una amenaza para otras especies. En algunos casos han ocurrido impactos sustanciales porque los enemigos naturales generalistas, utilizados como parte de un programa de control biológico, utilizaron otros recursos intensivamente además de la especie focal. Para minimizar los impactos no deseados, las regulaciones de la liberación de enemigos naturales son cada vez más estrictas como se evidencia en Nueva Zelanda y Australia. La Organización de Alimento y Agricultura está impulsando códigos voluntarios de buenas prácticas para promover la adopción generalizada de medidas de seguridad, que, de ser observadas, deben resultar en la selección de agentes con altos niveles de fidelidad de huésped y de hábitat. Los programas de control biológico en apoyo a la conservación se han enfocado tradicionalmente en especies herbáceas que amenazan las áreas naturales. Más recientemente, las plagas de artrópodos exóticos que compiten con la fauna nativa o dañan plantas nativas se han convertido en el blanco de programas de control biológico orientados a la conservación. La extensión del control biológico a nuevas especies de importancia para la conservación, tales como los invertebrados acuáticos invasores y vertebrados plaga, está garantizada. En muchos casos, los programas de control biológico cuidadosamente orquestados contra especies seleccionadas apropiadamente pueden ser la única forma factible de controlar especies invasoras que afectan a comunidades bajo asalto de exóticas cuando las opciones de prevención, contención y erradicación se hayan agotado o se consideren no factibles.

1 Answer 1

I think this partially depends on the timeframe. Endemism is usually divided into paleoendemism and neoendemism (see e.g. Kier er al in PNAS for use of both terms). Here, neoendemism is referring to the result of recent adaptive radiations that have led to new endemic species. This is then in contrast to paleoendemism, which refers to previously widespread species that are now confined to isolated areas.

Neoendemism is clearly related to your question, but whether dingos should be labelled as neoendemic depends on if it can be seen as a unique subspecies. If it is, it might be more suitable to view it as neoendemic and not exotic (nothing prohibits neoendemic species to be ecologically "problematic" to the previous fauna though).


Divide the youth into teams and assign each group three invasive species from the list below for their research.

  • Gypsy Moth
  • Kudzu
  • House Finch
  • Asian Long Horned Beetle
  • Periwinkle
  • Garlic Mustard
  • Emerald Ash Borer
  • Purple Loosestrife
  • Sudden Oak Death
  • Ambrosia Beetle
  • Asian Carp
  • European Starling
  • Tree of Heaven
  • Zebra Mussel

12.3C: Exotic Species - Biology

In this chapter, the taxonomy, life history and reproductive biology of eight economically important species are presented. A review of the biology of these species provides also the opportunity to present additional details about technologies developed in China for breeding and farming these species. The various cultural systems applied for sea farming and sea ranching are presented in Chapter 3.

These commercially important species belong to five taxonomic groups, as follows:

  • Kelp , a brown macroalga ( Laminaria japonica )
  • Lavers , red macroalgae (12 species of Porphyra )
  • Scallops , bivalves (four species, e.g. Chlamys farreri )
  • Abalone , gastropods (two species, e.g. Haliotis discus hannai )

2.1. Seaweed

Seaweed farming plays a very important role in China’s fishery industry for several reasons:

- Seaweed being autotrophic plants, no feeding is necessary for their growth and physical development. They can directly absorb and utilize nutrients present in their aquatic environment, such as nitrogen, phosphorus and other minerals.

- Seaweed farming is not only a clean industry, it also has a purification role in its environment, unlike shrimp and fish farming. Decades of field observations have revealed that a red tide never occurs in areas where seaweed are farmed, especially if it is kelp. On the contrary, in some areas where there is no seaweed farming, red tides are frequent.

- Because of the seaweed autotrophy, their farming requires relatively small investments.

- Seaweed have multiple uses, for example as human food, or to produce alginates and iodine, or to feed abalone and sea urchins.

2.1.1 Japanese kelp biology and culture

As mentioned earlier (see Section 1.3.2), research on and farming of Japanese kelp ( Laminaria japonica) were initiated in the 1940s. Following the development of modern breeding techniques in the early 1950s, great increases in production were gradually possible from 1958.

(a) Taxonomy and life cycle

Kelp (Figure 1) is a brown macroalga belonging to the phylum Phaeophyta. It is the only species of the genus Laminaria occurring in China, although more than 50 species have been reported world-wide and about 20 species are present in the Asia-Pacific region. Seaweed of the genus Laminaria have been given various common names, such as “kelp” in Europe and North America, “kombo” (large cloth) in Japan and “haidai” (sea ribbon) in China.

Kelp grows in temperate cold water zones. Although the species has been known in China for almost 80 years, under natural conditions it occurs only north of the 36°N latitude. In more southern latitudes, high sea water temperatures damage parent breeding stocks during the summer. This natural range was successfully extended southwards to the Fujian Province by using artificial rearing techniques, where young sporelings were grown indoors in refrigerated sea water before being transplanted to outdoor rafts for grow-out. Even with such techniques, commercial kelp farming was successful as far south as the 25°N latitude only. As a result, in China, Laminaria is present either naturally or artificially along the eastern coast of five provinces, from the Liaoning Province in the north to the Fujian Province in the south.

Male gametophyte plants produce male gametes called spermatozoids or antherozoids. Female gametophyte plants produce female gametes (eggs). At fertilization, male and female gametes fuse to form zygotes (2N), which subsequently develop into young sporelings at the beginning of the sporophyte generation (Figure 2).

Life history of Laminaria

Laminaria exhibits alternation of generations, the sporophyte generation alternating with the gametophyte generation.

It also exhibits heterothallism. The sporophyte plant is a large multicelled macroalga whereas the microscopic female and male gametophytes are only one cell or a few cells in size.

The asexual sporophyte generation (2N) produces motile zoospores (N), which develop into male and female gametophytes.

The sexual gametophyte generation (N) produces male and female gametes (N).

After a number of cell divisions, the microscopic male gametophyte plant develops several spermatangia (or antheridia), each one producing a single motile biflagellate spermatozoid, which is released into sea water.

The female gametophyte develops a single large oogonium, which produces an egg. The egg is extruded during ovulation but remains attached to the apical lip of the oogonium. Here the egg is fertilized by a motile spermatozoid, the fusion of male and female gametes producing the zygote (2N). This zygote germinates and develops into a young sporeling, or young seedling, which subsequently develops into a young sporophyte plant.

(b) Artificial sporeling production and farming techniques

The collection of zoospores is made from selected parent kelp plants which are first dried in the shade for a few hours. Then, they are submerged in sterilized and cooled sea water to stimulate the release of zoospores. These attached themselves to a substrate such as bamboo rods or ropes. They are reared in a greenhouse, in cooled and sterilized sea water, where they develop into gametophytes and later, into sporelings.

If zoospores are collected in mid-October, the resulting young sporophyte plants are called “autumn seedlings”, whereas zoospores collected in early July produce young plants called “summer seedlings”. Because of the zoospore collection practice, summer seedlings are produced three months earlier than autumn seedlings, thus gaining three months for additional growth. Such change in the breeding season has resulted in a great increase in production and in improved conditions for the farmers. So now, in China, only summer seedlings are used.

Nursing of young sporelings

As young sporelings 3 to 5 cm long become overcrowded in their breeding station, they are moved to grow-out sites when sea water temperature drops below 20°C, e.g. around mid-October in northern China. The purpose of such move is to stimulate their growth to a length of 10 to 25 cm before their transplantation. During this nursing period, young sporelings grow very rapidly.

Transplantation of young sporophytes

At the end of the nursing period, young seedlings are transplanted to kelp culture ropes for final grow-out on floating rafts. The procedure is similar to the transplantation of young rice plants in paddy culture.

Three types of floating raft are used for farming kelp, depending on farm site conditions, such as water depth, currents and nutrients content:

Rafts with horizontal ropes (Figure 3B) are widely adopted because they can be used under various sea conditions. Usually 10 to 40 floating rafts are anchored parallel to each other and spaced 3 to 5 m apart. The culture ropes are held in the horizontal position by tying both ends to other ropes. This method is suitable for shallow and deep sites. Its main advantage is that it can be very easily adjusted in different sites in response to changing conditions, such as turbidity and light intensity, as well as according to the different growth phases.

Dragon line rafts (Figure 3C) are well suited for either turbid inshore water or for open deep water with strong sea currents. Anchored at both ends, the floating raft is 50 to 60 m long and made of a series of vertical ropes attached at regular intervals of about 1.5 m. These ropes support a long horizontal culture rope. This farming method is used by most of the southern kelp farms.

Figure 3. Types of floating rafts for kelp culture

A. Raft with vertically hanging ropes

B. Raft with horizontal ropes

Harvesting usually takes about 40 days and it often needs additional temporary manpower (Figure 4). Timing of the harvest should be well planned in advance to prevent biomass losses as summer water temperature rises. If kelp is harvested too early, yield and quality will be reduced because kelp fronds will have a higher moisture content. On the other hand, if the harvesting takes place too late, the fronds will be deteriorated and invaded by parasites. Typhoons become more frequent also.

Since kelp farming has developed, the biomass of natural Laminaria stands has greatly increased. As there is no interest in harvesting them, they form an underwater forest which has become the habitat and the spawning ground for many aquatic animals and in particular for species with a high commercial value, such as sea urchins, abalone and sea cucumbers.

2.1.2. Laver biology and culture

Laver ( Porphyra spp.) is a red seaweed belonging to the Order Bangiales, Family Bangiaceae. There are about 70 species, distributed throughout the world from frigid to subtropical zones. In China, there are over 10 species with a commercial value. They are classified into three sections (Figure 5A) as follows:

In the Genus Porphyra , there are four types of sexual characteristics (Figure 5B):

Dioecism (a, b) ------------------------------------------------- P. dentata and P. pseudolinearis

Monoecism (c,d,e) --------------------------------------------- P. yezoensis and P. suborbiculata

Majority of dioecism + minority of monoecism (a,b,c) P. haitanensis

Monoecism + minority of male thallus (c,b)------------ - P. katadai Miura var. hemiphylla

Figure 5. Characteristics of the thallus and distribution of generative cells

B. a,b: dioecism and c,d,e,: monoecism

Porphyra species have a complex biological cycle (Figure 6), which is temperature dependent and seasonal in nature. Until 1949, it was still an enigma. British botanist K. M. Drew then discovered that the genus Porphyra existed during the warm season as a filamentous shell-boring stage, which he had previously described as a separate species, Conchocelis rosu .

During winter months, Porphyra thalli differentiate and produce spores of different sizes, by successive divisions of mother cells: the largest carpospores and the smaller spermatia. Carpospores are released and collected in April-May on suitable substrates, such as old oyster shells. These carpospores germinate when water temperature rises to 25°C, thus producing the conchocelis stage. This stage can recycle asexually through monospore production, conchospores being produced from September to October when water temperature decreases. Conchospores attach themselves to give sexually differentiated thalli, which are used to produce laver.

Figure 6. Life cycle of Porphyra species

(d) Breeding and farming techniques

In China, laver culture has a long history (Section 1.3.2), but the collection of carpospores as “seed” to produce laver thalli dates from the 1950s, following research carried out by Dr C. K. Tseng and his colleagues. This enabled the farming of two species of Porphyra , P. yezoensis in the northern regions (from northern Jiangsu Province to Shandong Province) and P. haitanensis in the southern regions (Fujian and Zhejiang Provinces).

Collection of carpospores

The production period of carpospores depends on species: for P. yezoensis, it is from December to May and for P. haitanensis, it is from November to March. In order to shorten the rearing period of conchocelis filaments in greenhouses and to select the best season for the germination of carpospores, their collection should take place in mid-May for P. yezoensis (optimum water temperature, 15-20°C) and in February-March for P. haitanensis .

During the maturation season, parent plants are collected and dried, removing 60 to 70 percent of their moisture content. The algae are then preserved in a freezer at -15°C to -20°C where they can be kept for several months. When the season for collecting the carpospores arrives, desiccated parent algae are washed two or three times with sterilized sea water. As soon as carpospores are released in the water, the latter is sprayed on substrates, such as clam shells. Carpospore density on these substrates varies from 200 to 400 cells/cm 2 .

Rearing of conchocelis filaments

Most of the attached carpospores will become conchocelis filaments two weeks later. These filaments can be seen with a magnifying glass and, 15 days later, with the naked eye.

From May to June, favourable development conditions are as follows:

There are three methods (Figure 7) for farming laver:

- Stake method. It is generally used in sites where there is no strong wind and no high waves. Routine operations and management are rather easy, but laver plants are exposed in the air for longer periods during low tides. Therefore, growth rate is lower than in the other two methods.

- Semi-floating method. Rearing facilities are installed in the intertidal zone. The netting frames float up during high tides and lie on the bottom, in the air, during low tides. This method is commonly used because it is much easier for routine management while producing good harvests. In general, production on a dry weight basis reaches 2400 kg/ha ( P. yezoensis ) or 5 000 kg/ha (P. haitanensis ).

- Floating raft method. It is similar to the method used for kelp farming (Section 2.1.1b). Netting frames always float at the water surface. Laver growth is increased, nutrient absorption from sea water by the thalli happening for a longer period of time than in the other two methods. But some fouling algae invade the nets, influencing laver quality subsequently. It then becomes important to control this fouling regularly.

Figure 7. Three methods for farming laver

2.2. Molluscs

2.2.1 Scallop biology and culture

Scallop is an economically important bivalve. As early as 30 years ago, world fishery production reached over 170 000 mt. Later, following overfishing, environment deterioration and increased consumption, captured scallop could not meet market demand any more. Scallop farming became a profitable activity in Asia and Europe. In the 1980s, it also became a prosperous aquaculture sector in China. By 1988, farmed scallop production was 122 000 mt. Recently, it reached one million metric tons.

Figure 8. Chlamys farreri (a) and Argopecten irradians (b)

In order to meet the soaring demand for scallop spat, research on reproduction started in the 1960s. By 1974, it became possible to produce spat on a commercial scale for Chlamys farreri (Figure 8a) . Then, in successive years, the technology was developed for Chlamys nobilis (1978), Patinopecten yessoensis (1981) and Argopecten irradians (1983 - Figure 8b). These four species are now successfully farmed in both northern and southern China.

P. yessoensis and A. irradians are exotic species introduced from Japan and USA in 1981 and 1982 respectively. The rearing cycle of the Japanese scallop being longer, its production through sea ranching is well developed in the Shandong and Liaoning Provinces.

The technology used for the production of scallop spat is almost the same as the one used for oyster. It may be schematized as follows:

In the following sections, scallop hatchery procedures are described taking as a concrete example those applied for the production of Chlamys farreri spat.

Selection and conditioning of broodstock

In late winter or early spring, broodstock is selected either from farmed stocks or from wild individuals captured on fishing grounds. They are then transferred to conditioning tanks where, on the first day, water temperature is kept 2 to 3°C higher than natural water temperature. On the next days, water temperature is increased daily by 1 or 2°C until it reaches 12-13°C for Chlamys farreri or 15-18°C for Argopecten irradians. This temperature is kept stable for three to five days to synchronize gonad development. Then, it is increased daily again until reaching the optimum temperature, about 18°C for C. farreri or 22-23°C for A. irradians .

During conditioning, broodstock is fed either an artificial diet or unicellular algae, mostly Phaeodactylum tricornutum, Chaetoceros muelleri, Monochrysis simplex, Isochrysis galbana, Tetraselmis tetrathele and Nannochloropsis oculata.

Broodstock spawning and reconditioning

Conditioned spawners are desiccated for two hours and then placed into tanks filled with running filtered sea water for one hour. To prevent multi-sperm fertilization of the eggs, female and male scallops are stocked in separate tanks until spawning.

Spawning takes place in tanks where water temperature is kept 2 to 4°C higher. This thermal shock stimulates spawners to release gametes within 10 to 15 minutes, for about 50 minutes.

After spawning, the spawned broodstock can be reconditioned during seven to ten days before inducing a second spawning. But, in practice, such reconditioning is used only when there is a shortage of broodstock.

Eggs fertilization and incubation

Chlamys farreri is a dioecious bivalve mollusc. During its reproductive season, eggs are released from the gonads into the water and fertilized. Fecundity of a mature female scallop may be as high as 3 to 6 million eggs. Diameter of the eggs averages 65 to 72 m. The fertilizing capacity of scallop sperm lasts longer than that of abalone: at 16 to 19°C, sperm retains its fertilizing capacity for 6 hours. After fertilization, egg density is kept at 20 to 30 eggs per millilitre for incubation.

Development from fertilized egg to spat is described in Table 15 and illustrated in Figure 9.

As larvae become trochophores or veligers, the selection of healthy larvae is initiated on the basis of their activity and attraction to light. Such larvae move to the upper water layer while the unhealthy larvae usually sink to the tank bottom. This is a simple but very important procedure which ensures production of a majority of high quality spat.

Table 15. Development of Chlamys farreri from egg to spat

Sea water temperature 18.2 - 25°C and salinity 25 - 30 ppt

Development and growth of scallop larvae depend on environmental conditions such as water temperature, salinity and food. For Chlamys farreri , suitable conditions are as follows:

- Optimum temperature: 17 to 20°C

- Water exchange rate: first 7 days from 1/3 to 1/2 afterwards, increasing up to 2 volumes per day

- Food and feeding regime: the following microalgae are commonly used for feeding scallop larvae: Phaeodactylum tricornutum, Chaetoceros muelleri, Monochrysis simplex, Isochrysis galbana, Tetraselmis tetrathele and Nannochloropsis oculata . Substitutes like yeast and microencapsulated feeds are used also, but live algae are better for the production of good spat. Recommended algal density varies as given in Table 16.

Table 16. Feeding microalgae to Chlamys farreri larvae

Algal density
(𣙨 cells/ml)


Installation of substrates

After 18 to 20 days at 17-19°C, larvae reach 165 to 180 m in length. During this period, appearance of the eye-spot indicates that larvae are about to become benthic organisms and to attach themselves to a substrate. Such substrates for larval attachment should be installed, just prior to this change of life style. Materials made of palm threads, nylon fibres or polyethylene fibres can be used for this purpose. Experience has shown that larvae prefer brown, red or yellow substrates.

Juveniles over 500 m long, also called young spat, become easily detached from their substrate, sinking to the bottom of the rearing tanks. In order to avoid this, they should be transplanted to a good nursery site on time.

During this nursing period, routine management is very important to increase survival rate. Every five to seven days, net bags should be cleaned to guarantee an adequate sea water exchange.

As young spat reach 2 mm in length, they should be transferred to other net bags with a larger mesh size, where they will grow up to their commercial size of 10 to 20 mm.

At present, some hatcheries have land-based nursing ponds built in greenhouses. This has the advantage of accelerating the growth of young spat in early spring because of the higher temperature of nursing pond water. Management is also easier.

(b) Sea farming and ranching techniques

The technology used for farming Chlamys farreri is schematized in Figure 10.

Sea ranching is widely practised in areas with a sandy or rocky bottom, 15 to 20 m deep. Before stocking young scallop, sea stars, crabs and other predators should be eliminated. Juvenile scallop are then experimentally stocked in a selected area. If survival rate is at least 60 percent one month later, the area can be selected for sea ranching. Stocking density ranges from 10 to 20 scallop juveniles per square metre. Commercial size may be reached 20 months later.

2.2.2 Abalone biology and culture

Abalone are large herbivorous marine gastropods. There are about 100 different species, all belonging to the same genus, Haliotis . They are found in both hemispheres, the largest species in temperate regions and the smaller ones in tropical regions. The greatest number of species is present in the central and south Pacific regions and in parts of the Indian Ocean, but none of them has a large size.

In China, two indigenous species are cultured, Haliotis discus hannai (Figure 11a) and H. diversicolor (Figure 11b) and its varieties. The former is mainly found in the northern part of China, such as the Shandong and Liaoning Provinces, the latter preferring the southern regions, the Fujian, Guangdong and Hainan Provinces. Young abalone of both species are produced in commercial hatcheries, most of which belong to private and collective entrepreneurs.

Figure 11. Haliotis discus hannai (a) and Haliotis diversicolor (b)

The technology used for the production of young abalone can be schematized as follows:

Development of H. discus hannai from egg to juvenile is described in Table 17 and illustrated in Figure 12.

Table 17. Development of H. discus hannai from egg to juvenile
(at water temperature 22.5 to 24°C)

Figure 12. Development of abalone from egg to juvenile

After hatching, actively swimming larvae are transferred from the upper water layer of spawning tanks to rearing tanks. Best stocking density is about 1 000 ind. per litre. Optimum water temperature is 20°C for H. discus hannai and 26-28°C for H. diversicolor.

Crawling larvae and juveniles

Following physiological and morphological changes, planktonic larvae search for a suitable substrate for their crawling life. After about one or two days, they develop into crawling larvae and settle on corrugated plastic sheets placed in the rearing tanks. To ensure that settlement of the larvae is evenly distributed, tank water should not be changed and light intensity should be kept below 100 lux for the first few days.

It is most important to control settlement density. Optimum survival rate and growth are obtained at densities of 100 to 200 individuals per 100 cm 2 , because at higher densities, benthic diatoms can not meet the food demand of growing larvae.

Water salinity has also a very significant effect on growth and survival as young abalone are typically stenohaline. Optimum salinity for larval development and grow-out ranges from 32 to 35 ppt. Both larvae and young individuals will die if the salinity falls below 24 ppt. Juveniles will die after 60 days in 25 ppt or 30 days in 20 ppt. All hatcheries and farming facilities should therefore be located away from estuarine areas.

As young abalone reach 5 mm shell length, they have to be dislodged from their settlement substrates and transferred to nursing substrates placed into indoor rearing tanks. In order to do this safely, anaesthetic chemicals are commonly used, such as alcohol, ethylcarbamate (NH 2 COOC 2 H 5 ) or ethylaminopionate (NH 2 C 2 H 4 COOC 2 H 5 ) (Table 18).

Table 18. Use of anaesthetic chemicals


Within four to five months, they grow to over 20 mm length. At this size, they can be sold for farming but, for sea ranching, juveniles need to be reared for another few more weeks, until they reach at least 30 mm long.

(b) Sea farming/ranching and stock enhancement

In Japan and China, initial development of the abalone industry dates from the late 1950s and early 1960s. Following successful research on mass production of seed (Table 19), abalone farming rapidly developed in the 1990s. By 1999, total world production reached about 13 000 mt, of which over 8 000 mt were farmed abalone. According to existing statistics, China is the world largest producer and in 1999, its farmed production was over 5 000 mt (Table 19 and Figure 13). Almost all of it is sold on domestic markets.

In China, there are two popular methods to farm abalone: the intensive method indoors and cage culture on floating rafts. Most of the farmers use seaweed as food. In northern China, brown seaweed such as Laminaria and Undaria are preferred, but in the southern regions, red seaweed (e.g. Gracilaria ) and formulated feeds are commonly adopted.

As production costs of the intensive system are higher, its use is often restricted to the production of small abalone (2.5 to 3 cm shell length) for the restocking of selected sites where wild seaweed are available. Within a couple of years, these abalone grow up to 6-8 cm length and they are then harvested by divers. Such ranching method giving a higher profit margin than farming, it has been widely adopted in northern China. Recently, the price per kilogram of commercial size abalone has reached US$50 to 60, depending on size.

The technology to produce hybrid and triploid abalone has been successfully developed by researchers. It is ready to be introduced to the commercial production sector.

Table 19. Abalone: production of seed and commercial size, 1991-1999

2.3 Crustaceans

2.3.1 Shrimp biology and culture

China has a great diversity and abundance of marine shrimp. There are about 100 species, among which 40 have a high commercial value (Liu, R.Y.1955 Liu and Zhong, 1986). Due to overfishing, production of Penaeus chinensis in the Bohai Sea and the Yellow Sea declined from 32 896 mt in 1980 to 7 324 mt in 1982. In order to meet the increasing demand and to protect natural resources, shrimp farming and enhancement became priority subjects from the late 1970s to the early 1980s.

Nine species of shrimp belonging to three different genus are farmed in China:

Penaeus chinensis
(syn. P. orientalis)

L. vannamei and L. stylirostris are exotic species, introduced from America. They have become very popular (especially L. vannamei ) for farming in inland areas, using brackish water initially and then gradually diluting it until obtaining fresh water.

But in China, research has concentrated much longer on the farming of Chinese shrimp ( Penaeus chinensis syn. P. orientalis ) and it is this species which will be considered in the next sections.

Shrimp broodstock may be obtained from three sources:

- Soon after the spawning migration, it may be captured on spawning grounds. Presently, this is the main source of broodstock in northern China. Shrimp can be spawned soon after capture and they are the least expensive. But there is concern that continued use of such broodstock is threatening wild stocks and that it impacts on ocean fishery production negatively.

- Broodstock may be captured during its reproductive migration, before being sexually mature. It is then held in ponds until it becomes ready to spawn.

- Broodstock may be collected either from farm ponds at the end of summer or from the sea during the wintering migration. Shrimp are then overwintered in tanks or ponds. They are spawned the following spring when they become sexually mature. At present, this method is widely used. It has the least impact on natural resources.

P. chinensis is a typical multiple spawner. Under hatchery conditions, a female can spawn four to five times, at the average interval of 15 days (range: 5 to 20 days). Egg production per spawning varies from 400 000 to 500 000. One female can produce about 1.7 million eggs during its spawning season.

Since spawning usually occurs at night, gravid females are selected and placed in spawning tanks in the afternoon or at dusk. Fertilized eggs are collected on the next morning.

Hatching and larval development

Water quality and ambient conditions are especially important for ensuring a high hatching rate, normal embryonic development and production of healthy nauplii. In China, good hatching conditions are defined as follows:

Depending on water quality and temperature, postlarvae (PL) are ready for pond stocking 20 days after hatching. They are then typically 7 mm long. Their transfer from the hatchery to the farm is done by truck, in canvas barrels. A barrel of 1 m diameter containing 20°C aerated water can hold 300 000 to 400 000 PL 7 to 10 mm long, for six to eight hours, without excessive mortality. PVC plastic bags filled with water and oxygen are also used. A 10-litre bag can hold 10 000 to 20 000 PL for 10 hours or more.

Successful pond farming of P. chinensis depends on a series of procedures which should all be optimized, such as site selection, pond construction, PL transport and stocking, predator control, water quality management, feeding, disease control and harvesting.

In China, several cultural systems are used to farm shrimp, including: fish pond polyculture, shrimp monoculture without feeding, shrimp monoculture with feeding and pen culture in open waters (see Chapter 3).

The first two systems are extensive, with low yields and limited economic efficiency. But since 1993 (epidemic viral disease), a disaster year for the shrimp industry in China, these extensive systems have been widely preferred because both risks and production costs are lower.

For pond culture, site selection is most important, especially with respect to elevation and topography, soil conditions and water quality. For best results with P. chinensis , water pH should be in the range of 7.8 to 8.6 and salinities from 5 to 35 ppt. Metal ions should not exceed the following values: Hg 2+ 0.0002 mg/l, Cu 2+ 0.017 mg/l, Zn 2+ 0.03 mg/l and Pb 2+ 0.16 mg/l. Sandy clay makes the best pond bottom: it is firm and impermeable, and it does not crack excessively when dry. Acid sulphate soils are not suitable because their oxidation forms sulphuric acid, decreasing pH and solubilizing iron and aluminium. These last two ions are not only toxic, but they also bind phosphorus and thus lower pond productivity. Other factors to consider when siting a farm include availability of labourers, reliable source of postlarvae for stocking, vehicle access to the ponds, local climate (precipitation, temperature) and post-harvest processing.

Precautions should be taken to minimize shrimp losses due to diseases and predation. Thorough drying of the pond bottom between crops will help reduce pathogens and solubilize nutrients in non-acid soils. Since 1993, great efforts have been made in the prevention of viral diseases, such as using Special Pathogen Free (SPF) broodstock and applying chemical treatments to reduce the risk of epidemics and great financial losses. But for curing these diseases, existing treatments are still unsatisfactory.

In extensive farming systems, increasing natural food production in ponds improves shrimp growth and lowers production costs. In China, to this end, Corophium spp. are stocked in ponds, giving good results. Other food organisms such as Unciola spp, Gammarus spp. and polychaete worms are also widely used.

(e) Shrimp stock enhancement

Experiments on the enhancement of shrimp stocks through stocking of postlarvae were carried out from the 1980s to the early 1990s (Section 3.8). Even if recapture rate was reported to be as high as 8 percent, the project was stopped because such method was judged to be too unreliable. Our full understanding of all processes involved in such enhancement is still far from being complete.

2.3.2 Mud crab biology and culture

The mud crab, Scylla serrata (Figure 14a), is an economically important crustacean occurring in tropical regions of the Indian and Pacific Oceans. It has been widely cultured in China, especially in the southern regions such as the Fujian, Guangdong and Hainan Provinces.

(a) Life habits and reproduction behaviour

Mud crab is a euryhaline animal which can tolerate water salinities ranging from 5 to 33.2 ppt. Optimum salinity ranges from 13.7 to 26.9 ppt. When salinity decreases below 7 ppt, they often dig holes to survive adverse environmental conditions.

Optimum temperature ranges from 180°C to 32°C. Feeding rate decreases when water temperature drops below 18°C. Crabs will survive in holes when water temperature drops as low as 12°C. As water temperature continues to drop to 7°C, they stop feeding and become dormant. During the hot season, as water temperature rises up to 35°C, they feel obviously unadapted, erecting their body and keeping their abdomen away from the earth when crawling on the sea beach. A grey-red spot appears on their tergum and, as water temperature increases above 39°C, they gradually emaciate until death.

Figure 14. Mud crab (a) and a berried female (b)

Crabs moult 13 times during their life span: six times during the larval stage, six times during the grow-out stage and once during reproduction. Moulting occurs only when water temperature is at least 15°C, but preferably when it is above 18°C. When crabs moult, they breathe rapidly, their oxygen consumption being higher. For two to three hours, newly moulted crabs cannot swim and lay on the bottom.

Scylla serrata is a carnivorous animal, its preferred food consisting of small molluscs, trash fish and other crustaceans.

Usually, the mud crab reaches the reproductive stage when its shell width is greater than 7.8 cm and its body weight over 100 g, females being normally a little bigger than males (shell width over 8.5 cm and body weight over 130 g).

Reproduction season varies according to local water temperature. In southern China, female crabs carrying eggs are few in winter, but in tropical regions, they can be found almost throughout the year.

Mating occurs about one hour after moulting of the female. The male turns the female on its back and climbs upon its abdomen. Then, it grasps the female with its walking legs, the female opening its abdominal plate. The male inserts his copulating apparatus into the female’s aperture genitalis and ejaculates sperm into the spermatheca.

Generally, mating lasts for one or two days, a period which may vary from nine hours to three days. After mating, the aperture genitalis is blocked by ovarian secretions. Mating occurs mostly at night, especially at the beginning of the high tide. For mating to be successful, water temperature should preferably be higher than 18°C.

Both female and male crabs do not feed during the mating period. After mating, females consume a large amount of food to support rapid ovarian development. Under suitable conditions, ovulation may take place 30 to 40 days later.

Normally, spawning occurs early in the morning, between 0500 h and 0800 h. Eggs are released from the aperture genitalis to meet the sperm released from the spermatheca. After fertilization, two-membrane layers are formed to protect the fertilized eggs. The inner one is a yolk membrane, the outer one being a secondary ovarian membrane. Fertilized eggs stick to the bristles of the abdominal legs of the female which is then called a “berried” crab (Figure 14b). One female crab can produce about 2 million eggs.

Development of fertilized eggs is accelerated by an increase of water temperature. At 18°C to 28°C, hatching occurs after 25 to 15 days, while at 32°C, it takes 11 days only.

A newly hatched embryo of Scylla serrata is called a zoea larva (Figure 15A). This zoea stage is made of five sub-stages, the zoea larvae developing into megalopa larvae (Figure 15 B) through five moults. Then, through another moult, these megalopa larvae metamorphose into juvenile crabs (Figure15 C). Normally, it takes 23 to 24 days at 26-29°C for the zoea larvae to develop into young crabs: 4 to 5 days from sub-stage I to sub-stage V and 6 to 7 days from megalopa to juvenile.

The megalopa larvae gradually adapt themselves to a benthic life. Because of their phototaxic behaviour, larvae are often attracted by light at night.

The moulting process depends on body size and environmental factors. For example, moulting of big crabs takes longer than for small ones. Newly moulted mud crabs lose their swimming ability and sink to the bottom of the pond. It takes two to three hours for soft-shell individuals to regain this swimming ability. Hardening of the shell lasts six to seven hours, three to four days being needed to complete this process. With each moult, shell width, shell length and body weight generally increase by about 28.4 percent, 30 percent and 41 percent respectively.

Strong stimuli or mechanical damages often result in the loss of appendages, a process called self-cutting. New appendages can be regenerated several times.

Selection and rearing of broodstock

Crab broodstock can be collected either from the wild or from farm ponds. The selected individuals should be healthy, with a body weight of over 300 g and ovaries having reached development stage V. Berried females are not selected as broodstock due to a lower fertilization rate and their contamination by parasites, such as ciliates, and by disease pathogens.

Broodstock rearing consists in ensuring maturation, reaching the berried stage and bringing the eggs close to hatching. Concrete tanks and earthen ponds can be used for this purpose. The facilities and equipment used for shrimp rearing in ponds are particularly well adapted for rearing crab broodstock, except that shelters made of bricks or stones should be added on the bottom of the ponds.

In concrete ponds, stocking density is usually less than two crabs per square metre. A higher density could result in fights and injuries. A rich and diversified food is required, which includes small mussels, fish, crab, shrimp, etc. Crabs are fed in the evening and feeding rate is determined by the amount of food left over on the next morning.

Optimum salinity ranges from 26 to 31 ppt. If salinity is lower than 22 ppt, ovarian development slows down. Similarly, development is slower at water temperatures below 20°C and crab will die at temperatures higher than 32°C.

Artificial aeration is needed in concrete ponds and there should be one complete water exchange daily.

Under good management, mature female crab should be reared about 10 days before spawning, even if well selected. After spawning and during the whole incubation period, it is very important to feed berried females a high quality food, to control water quality and to keep a rational stocking density.

Observing the colour changes of carried eggs is an important routine work. With the development of the embryos, this colour varies from bright orange, to grey and to dark-grey. When this last egg colour is reached, it indicates that the larvae will hatch soon. The duration of the incubation period depends on water temperature as shown in Table 20.

12.3C: Exotic Species - Biology

The family Siricidae consists of ten extant genera and 122 species worldwide, and is commonly referred to as wood wasps or horntails (Schiff et al. 2012, Smith and Schiff 2002, Morgan 1968, Benson 1950). Four genera have been recorded in Florida (representing six species): Eriotremex Benson, Sirex Linnaeus, Tremex Jurine and Urocerus Geoffroy (Leavengood and Smith 2013). Eriotremex is a small genus of 13 species that range from Japan and Taiwan to eastern India and Papua New Guinea (Smith 2010) with one species, Eriotremex formosanus, introduced to North America. The earliest records of this introduction are from several counties in Florida and Georgia in 1974 (Smith 1996). It has since become the most common wood wasp in Florida (Smith 1996).

Figure 1. Adult female wood wasp, Eriotremex formosanus (Matsumura). Photograph by You Li, University of Florida.

Synonymy (Back to Top)

Tremex formosanus Matsumura 1912, Eriotremex formosanus Benson 1943

The genus Eriotremex belongs to the subfamily Tremicinae of the family Siricidae. The genus was last reviewed by Smith (2010), who described a new species and provided some new distributional records for the other 12 species. Eriotremex formosanus is the only species of this genus adventitiously introduced to North America.

Distribution (Back to Top)

The type species of Eriotremex formosanus was collected from Formosa, the historical Portuguese name for Taiwan. Taiwan wood wasp taxonomist Maa (1949, 1956) recorded Eriotremex formosanus in Vietnam and suggested it may also be present in surrounding areas of Indo-China. Gangrou (1983) found Eriotremex formosanus from Yunnan province in southern China. Togashi and Hirashima (1982) and Togashi and Inoue (2007) recorded Eriotremex formosanus in Honshu, Japan. More recently, Smith (2010) recorded specimens collected in Laos.

Following its introduction into the US, it has been documented throughout much of the Southeast (Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas and Virginia) as well as Utah (Chapin and Oliver 1986, Stange 1996, Smith and Schiff 2002, Schiff et al. 2006, 2012, Warriner 2008).

Figure 2. World distribution of Eriotremex formosanus (Matsumura). Illustration by You Li, University of Florida.

Description (Back to Top)

As with most wood wasps, Eriotremex formosanus exhibits distinct sexual dimorphism (male and female are quite different in appearance). Adult females have a 3 cm long body with a 4 cm wingspan. The short, blunt, antennae each consist of 20-21 black antennal segments that are sometimes lighter in color at the base and apex. The metatibia bears one apical spur. The females&rsquo abdomens consist of black segments, some of which have yellow bands. The thorax is yellow, and long, golden setae (hair-like projections) cover the body throughout.

Originally, Stange (1996) stated that no males of this species have ever been collected. However, Schiff et al. (2006) presented an illustration of the first male from specimens reared in the United States. It was mostly black, with some yellow on the abdominal segments. Leavengood and Smith (2013) illustrated a male with an overall yellow color, with some black markings on most segments of the hind legs. These differences imply that the coloration of the male may be variable.

Diagnosis (Back to Top)

In Florida, there are six species of Siricidae: Eriotremex formosanus (Matsumura), Sirex areolatus (Cresson), Sirex nigricornis Fabricius, Tremex columba (Linnaeus), Urocerus cressoni Norton, Urocerus taxodii (Ashmead) and Sirex noctilio Fabricius. They had been reviewed by Leavengood and Smith (2013) who also provided a key for all of Florida's six Siricidae species.

Eriotremex formosanus differs from other Siricidae species with antennae bearing 20-21 segments (Fig 3A) (other species have either more or fewer) both sexes with only one apical metatibial spur (Fig 3B) and body with long golden hairs (Figs 3C, D).

Figure 3. Eriotremex formosanus (Matsumura). A- antenna. B- metatibial spur. Abdomen (C) and mesonotum (D) with long golden setae (hair-like projections). Photographs by You Li, University of Florida.

Biology (Back to Top)

The biology of Eriotremex formosanus is not well known. Adults have been collected year-round in Georgia (Smith and Schiff 2002), though the majority are recorded from April to June and September to November. This suggests two peak flights a year, but few conclusions can be drawn from these data. Some specimens were collected using UV light traps. In the southeastern US, Eriotremex formosanus is abundant in both upland pine-dominated forests and bottomland hardwood forests (Ulyshen and Hanula 2010) and can develop in logs, but strongly prefers snags. Many siricids take two or more years to complete their life cycle, though Eriotremex formosanus may have one or more generations a year, which may explain its rapid spread after introduction to the US (Smith, 1996).

Hosts (Back to Top)

Whereas most siricid species in North America feed on gymnosperms, Eriotremex formosanus associates most strongly with angiosperms. Host trees in its native range are currently unknown (Smith 2010) but reported hosts in North America include various oaks (e.g., Quercus nigra, Quercus phellos, Quercus alba and Quercus laurifolia), hickory (Carya spp.), and sweetgum (Liquidambar styraciflua). The species has also been reported from two pine species (Pinus palustris and Pinus elliottii) but conclusive evidence the species can complete development in gymnosperms is lacking (Stange 1996, Smith and Schiff 2002). In South Carolina, Ulyshen and Hanula (2010) found Eriotremex formosanus to strongly prefer water oak (Quercus nigra) over sweetgum and found the species to be absent from loblolly pine (Pinus taeda).

Management (Back to Top)

Unlike the European woodwasp, Sirex noctilio Fabricius, the Asian woodwasp, Eriotremex formosanus, is not considered an economically important pest because it only attacks dying or dead trees (Warriner 2008). However, the species may someday prove to be a pest and its ecological impacts in North American forests remain unknown (Ulyshen and Hanula 2010). There are no native North American parasitoid wasps or nematodes which could assist in managing Eriotremex formosanus populations. Prevention of the movement of firewood and other wood products into uninfested areas is the most judicious method to control the spread of wood wasps. However, it is not expected to prevent the natural dispersal of the insect. Methyl bromide treatment and heat treatment are two effective methods to kill wood wasp larvae and pupae in the wood.

Selected References (Back to Top)

  • Benson RB. 1950. An introduction to the natural history of British sawflies (Hymenoptera: Symphyta). Transactions of the Society for British Entomology 10: 45-142.
  • Chapin JB, Oliver AD. 1986. Records of Eriotremex formosanus (Matsumura), Sirex edwardsii Brullé, and Neurotoma fasciata (Norton) in Louisiana (Hymenoptera: Siricidae, Pamphiliidae). Proceedings of the Entomological Society of Washington, 88.
  • Gangrou X, Jian W. 1983. A study of the Siricidae in China. Supplementary Issue of Forestry Science, 1-29. [in Chinese]
  • Leavengood Jr JM, Smith TR. 2013. The Siricidae (Hymenoptera: Symphyta) of Florida. Insecta mundi 0309: 1-16.
  • Maa TC. 1949. A synopsis of Asiatic Siricoidea with notes on certain exotic and fossil forms (Hymenoptera, Symphyta). Musée Heude, Notes d&rsquoEntomologie Chinoise 8: 11-189.
  • Maa TC. 1956. Notes on the genus Eriotremex Benson (Hymenoptera: Siricidae). Proceedings of the Hawaiian Entomological Society 16: 91-94.
  • Morgan FD. 1968. Bionomics of Siricidae (Hymenoptera). Annual Review of Entomology 13: 239-256.
  • Smith DR, Schiff NM. 2002. A review of the siricid woodwasps and their ibaliid parasitoids (Hymenoptera: Siricidae, Ibaliidae) in the eastern United States, with emphasis on the mid-Atlantic region. Proceedings of the Entomological Society of Washington 104: 174-194.
  • Schiff NM, Goulet H, Smith DR, Boudreault C, Wilson AD, Scheffler BE. 2012. Siricidae (Hymenoptera: Symphyta: Siricoidea) of the Western Hemisphere. Canadian Journal of Arthropod Identification 21: 1-305.
  • Schiff NM, Valley SA, LaBonte JR, Smith DR. 2006. Guide to the siricid woodwasps (Hymenoptera) of North America. United States Department of Agriculture Forest Service, Morgantown, West Virginia 102 pp.
  • Smith DR. 1975. Eriotremex formosanus (Matsumura), an Asian horntail in North America (Hymenoptera: Siricidae). U. S. Department of Agriculture, Cooperative Economic Insect Report 24: 851-854.
  • Smith DR. 1996. Discovery and spread of the Asian horntail, Eriotremex formosanus (Matsumura) (Hymenoptera: Siricidae), in the United States. Journal of Entomological Science 31: 116-171.
  • Smith DR. 2010. The woodwasp genus Eriotremex (Hymenoptera: Siricidae), a review and a new species from Malaysia. Proceedings of the Entomological Society of Washington 112: 423-438.
  • Stange LA. 1996. The horntails (Hymenoptera: Siricidae) of Florida. Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Entomology Circular 376: 1-3.
  • Togashi I, Hirashima Y. 1982. Wood wasps or horn tails of the Amami-Oshima Island, with description of a new species (Hymenoptera: Siricoidea). Esakia 19: 185-189.
  • Togashi I, Inoue S. 2007. Distributional northernmost record of Eriotremex formosanus (Matsumura), and newly recorded woodwasps and sawflies from Fukui Prefecture, Honshu, Japan. Bulletin of the Biogeographical Society of Japan 62: 39-41.
  • Ulyshen MD, Hanula JL. 2010. Host-use Patterns of Eriotremex formosanus (Hymenoptera: Siricidae) in South Carolina, USA. Entomological News 121: 97-101.
  • Warriner MD. 2008. First record of the Asian horntail, Eriotremex formosanus (Hymenoptera: Siricidae), in Arkansas, U.S.A. Entomological News 119: 212-213.

Authors: You Li, School of Forest Resources and Conservation, Jiri Hulcr, School of Forest Resources and Conservation and Entomology and Nematology Department, University of Florida.
Photographs: You Li, School of Forest Resources and Conservation, University of Florida.
Web Design: Don Wasik, Jane Medley
Publication Number: EENY-628
Publication Date: June 2015. Reviewed February 2018.

An Equal Opportunity Institution
Featured Creatures Editor and Coordinator: Dr. Elena Rhodes, University of Florida


Experimental design

We established 160 experimental mesocosm communities (Supplementary Fig. 12), where interactions between plants, invertebrate herbivores and soil biota were manipulated and measured. A previous paper reports the ecosystem level outcomes for the same mesocosms 55 , but this paper is the first to explore individual plant–herbivore interactions. Each mesocosm consisted of a 125 L steel pot, with a bottom layer of 22 L of gravel to aid drainage out of the open bottom, 88 L of pasteurised soil and sand (50:50 mixture) and a top layer of 12 L of soil inoculum (see soil treatment details below). Mesocosms were planted with one of 20 unique communities, each consisting of eight plant species (Supplementary Table 23) selected from a pool of 39 plant species that co-occur in New Zealand grassland communities (19 natives, 20 exotics, Supplementary Table 24). Plant species were selected based on their occurrence at sites where inoculum soil was collected, and communities were designed to vary orthogonally in their proportion of exotic and woody species (0–100% and 0–63%, respectively, Fig. 5). The 20 exotic plant species occur along a spectrum of invasiveness, although 90% are considered to have significant negative impacts in New Zealand conservation (75% of the 20 plant species) 80 or agricultural land (50%) 81 . Plants were grown from seed or cuttings collected from New Zealand’s South Island (see Waller et al. 2020 55 for propagation details) and seedlings were randomly positioned in a ring, equally spaced around the centre of the pot during March 2017. Consistent positioning of plant species was used for replicates within each plant community, with plant communities replicated eight times to allow the application of herbivore and soil treatments (described below), and with replicates arranged together to minimise any environmental gradients.

The upper portion of the figure shows the experimental design (A), with orthogonal exotic and woody gradients of the 20 unique plant communities (numbered, with the community used for the ‘away’ soil treatment in parentheses), where plant provenance, functional group and plant species are represented by symbol colour (blue = native plant species, orange = exotic plant species), outline (solid = herbaceous, dashed = woody), and pattern (key in Supplementary Table 24), respectively. Also shown are details of the herbivore (mesh cages with herbivore addition and exclusion) and soil (plant–soil feedback ‘home’ = soil from conspecifics and ‘away’ = soil from heterospecifics) treatments The lower portion of the figure details the data collected for analyses (B), including plant and herbivore biomass, herbivore diversity, herbivore chewing and scraping damage, and the equation for pairwise potential for apparent competition 86 . Symbols courtesy of the Integration and Application Network (

To answer our research questions, we manipulated invertebrate herbivores (+Herbivore vs. −Herbivore) across mesocosm communities (Fig. 5). All mesocosms were covered with large mesh cages (Supplementary Fig. 13) (0.58 mm Cropsafe Mesh, 15% shade factor, Cosio Industries, Auckland, New Zealand) to keep added herbivores enclosed and deter most naturally occurring external herbivores (see Supplementary Methods for detailed description of cages). Herbivore populations were deliberately established in 80 mesocosms. Thirteen herbivore species that were added successfully established, along with seven self-colonising species, totalling 20 different species (establishment success and other herbivore species characteristics are detailed in Supplementary Table 25). These species were all polyphagous or oligophagous (see host ranges in Supplementary Table 25 and description of herbivore introductions in Supplementary Methods) and included seven native and 13 exotic herbivores from multiple feeding guilds (leaf and root chewers, suckers and miners). Each herbivore species was added to all +Herbivore mesocosms in equal density, regardless of whether a known host plant was present. Herbivore additions were staggered depending upon availability and some species were added multiple times to increase probability of establishment success and maintain populations (see Supplementary Methods for detailed description of protocols for each herbivore species). All self-colonising species were regularly removed from −Herbivore mesocosms, including spillover from intentional additions, but were allowed to establish populations in +Herbivore mesocosms. Several of the herbivore species produced multiple generations in the mesocosm communities (i.e., multiple life stages observed, or more individuals observed than were introduced), such as leafrollers, aphids, leafhoppers and slugs, and these are noted in Supplementary Table 25. Overall, our goal was not to replicate natural plant–herbivore communities, but to capture how native and exotic plants interact with a consistent suite of herbivores in novel communities, the preference and performance of the herbivores and potential consequences for indirect effects. We complied with all relevant ethical regulations for animal testing and research no formal ethics approval was required as invertebrate insect herbivores are not covered by ethics oversight in New Zealand.

The herbivore exclusion treatment was highly effective, reducing herbivore species presence on plants by 79% (generalised linear mixed model: F1,585 = 584.68, P < 2.2e −16 Supplementary Fig. 14A), herbivore species biomass per plant by 84% (linear mixed model: F1,137 = 651.55, P < 2.2e −16 Supplementary Fig. 14B), herbivore species richness per mesocosm by 59% (linear mixed model: F = 152.10, P < 2.2e −16 Supplementary Fig. 14C), herbivore chewing and scraping damage per plant by 24% (generalised linear mixed model: F = 276.22, P < 2.2e −16 Supplementary Fig. 14D), and PAC exerted and recieved by 98% (linear mixed model: F1,139 = 342.64, P < 2.2e −16 Supplementary Fig. 14E) and 99.5% (linear mixed model: F1,139 = 275.50, P < 2.2e −16 Supplementary Fig. 14F), respectively. Therefore, only data from the +Herbivore mesocosms were used to test our predictions, except for those relating to normalised degree and net herbivore impacts on plant biomass production (predictions 1b, 2a and 2b in Table 1 see statistical analyses below).

The herbivore treatment was crossed with a soil biota manipulation (‘home’ vs. ‘away’), as part of another study 55 (Fig. 5). Soil biota was manipulated using a modified plant–soil feedback approach 48 , where we grew each plant species in monoculture in 10 L pots of field-collected soil and pasteurised sand (50:50 mix) prior to the experiment to culture their associated soil biota. These conditioned soils were harvested after 9–10 months and used to create ‘home’ and ‘away’ soil inoculum mixtures for each plant community that were added to the mesocosms. ‘Home’ soils contained conditioned soils mixed from the eight species occurring in that community, and represent soils from an established invasion that contain both specialist and generalist soil biota. On the other hand, ‘away’ soils contained conditioned soils mixed from eight species occurring in one of the other 19 communities, but where a focal species did not occur. These ‘away’ soils represent previously uninvaded and thus contain no specialist soil biota. Therefore, although the soil treatment was not the main focus of this paper, it allowed us to test how specialist soil biota moderate plant–herbivore interactions in established versus new invasions, and we retained it as an explanatory variable in analyses to control for its potential effects.

Data collection

We measured herbivore richness, biomass, leaf damage by chewing and scraping herbivores and plant biomass (full list of response variables in Supplementary Table 26) (Fig. 5). Herbivores were surveyed on eight occasions: May, June, July, August, September and November in 2017 and January and April in 2018. For each survey, we counted the number of individuals of each herbivore species that were observed feeding on each plant. For species that reached high densities (e.g., aphids), abundance was estimated by surveying a portion of the plant and extrapolating to the entire plant. For some highly mobile or belowground herbivores it was difficult to reliably characterise feeding interactions through direct observation. For these species, we used restriction fragment length polymorphism (RFLP) to identify host plants with DNA extracted from frass, regurgitate or gut contents (see Supplementary Methods for detailed description of molecular protocols). Finally, because we could not practically measure the biomass of each individual herbivore from each mesocosm, we converted raw abundances to a standardised estimate of herbivore biomass for each species using mean dry biomass of a random sample of ten individuals. To calculate the mean biomass of each herbivore species for each individual plant, we multiplied the total abundance of the herbivore by its mean dry biomass per individual, and then divided by the number of times that plant was surveyed (plants that died were surveyed less than eight times). To estimate total mesocosm herbivore biomass, we multiplied the mean dry biomass per individual for each herbivore species with its total abundance across all surveys, and then summed across all herbivore species.

For each survey, we also assessed leaf damage by chewing and scraping herbivores on each plant against six different categories (0 = no damage, 1 = 1–5% leaf area chewed or scraped, 2 = 6–25%, 3 = 26–50%, 4 = 51–75%, 5 = >75%). We used these categories because of the large number of plants to survey and the difficulties of non-destructively measuring percent leaf area removal at finer resolution in situ. We obtained an overall estimate of damage throughout the experiment by transforming the categories to median percent damage values (e.g., category 3 = 38%) and calculating mean percent damage per survey for each plant. Finally, plants were harvested after 1 year, above- and belowground biomass separated and washed, dried at 65 °C, and weighed. Additional methodological details are described in Supplementary Methods and Waller et al. (2020) 55 .

Data analysis

For each response variable, we used (generalised) linear mixed effects models to ask whether native and exotic plants (and native-dominated and exotic-dominated communities) differed in their direct (predictions 1a–c and 4a in Table 1), indirect (predictions 3a and 4b) or net (predictions 2a, b) interactions with herbivores and soil biota. For analyses at the individual plant level, each model included plant provenance (native, exotic), the soil treatment (‘home’, ‘away’), and their interaction as fixed effects (Supplementary Table 26 contains model structure details), with plant species and mesocosm nested within plant community as random effects. To assess how herbivores influenced the biomass production of native and exotic plants, we used data from all mesocosms and included the herbivore treatment and its interactions in the model. Post hoc pairwise contrasts involving more than two treatment combination levels (i.e., interactions) were conducted using Bonferroni corrected Tukey tests. For analyses at the mesocosm level, each model included the proportion of exotic species planted in the community (0–100%), the soil treatment and their interaction as fixed effects, with plant community as a random effect (mesocosm was nested within plant community for analyses of herbivore biomass and herbivore:plant biomass ratio to account for the non-independence of native and exotic herbivores occurring on the same plant). For analyses of herbivore species’ presence, herbivore biomass, and herbivore:plant biomass ratio, the herbivore provenance (native, exotic) was also included as a fixed effect and herbivore species and mesocosm nested within plant community as random effects.

The number of observations and model error distributions used varied depending upon the response variable and some response variables were transformed to meet model assumptions (summarised in Supplementary Table 26). For analyses of herbivore presence, we retained absent interactions (i.e., zeroes in the data) that were within the fundamental host range for each herbivore species (based on the experiment-wide meta-web i.e., the herbivore species fed on the focal host in at least one mesocosm) and discarded data for those that were not. Herbivore biomass was assessed using a two-stage model, where we first examined treatments that were influential to the presence or absence of herbivore species on plants within their fundamental host range, followed by secondary analyses to assess herbivore biomass only on plants where herbivores were present. Herbivore presence was modelled using a binomial error distribution, while herbivore biomass was log-transformed and modelled using a normal error distribution. Normalised degree did not require transformation and was modelled using a normal error distribution. Herbivore species richness per mesocosm was also untransformed and was modelled using a Poisson error distribution. Percent leaf damage from chewing and scraping invertebrate herbivores was analysed using a gamma error distribution with a log link function, and was logit-transformed before a constant of 5 was added to conform to the gamma distribution. Both measures of PAC were log-transformed and modelled using a normal error distribution. Dead plants were excluded from analyses of plant biomass, which was log-transformed and modelled using a normal error distribution.

For all plausible models, Cook’s D and quantile-quantile plots were used to identify potentially influential data points. However, in no case did removal of these data points qualitatively change model conclusions, thus we retained them in analyses. All model assumptions were tested for and satisfied, and Poisson and binomial models were checked for overdispersion, with none detected. We report estimated marginal means and standard errors from fitted models, back-transformed when appropriate.

We used normalised degree (i.e., the proportion of herbivore species that fed upon a given host plant out of the total herbivore species in the mesocosm) to quantify herbivore richness for each plant, because the number of invertebrate species that established varied among mesocosms. Measuring the plant–herbivore interactions of the entire community allowed us to estimate each species’ potential for apparent competition (PAC). PAC is a metric devised by Müller et al. (1999) 86 that describes the sharing of interaction partners between two species in a community, and has been previously used to predict outcomes of indirect interactions in host–parasitoid communities 43,44,45 . To estimate PAC for each host plant species pair in a given mesocosm, we calculated dij, the proportion of herbivore biomass attacking plant species i that is shared with plant species j. In the equation for pairwise PAC below (see also Fig. 5), α represents link strength (i.e., herbivore biomass), i and j are the focal pair of host plant species, m is all plant species from 1 to H (the number of plant species in the community), k is a herbivore species, and l is all herbivore species from 1 to P (the number of herbivore species in the community) 86 .

After calculating pairwise PAC between all plants within each mesocosm, we quantified the potential for focal species i to exert apparent competitive effects (PACexerted) by summing PAC values for the focal species on all other community members (excluding intraspecific PAC PAC = 0 if plants shared no herbivores). We also quantified the potential for focal species i to receive apparent competitive effects (PACreceived) by summing pairwise PAC values from all other community members to the focal plant. Because PAC should vary with the total number of herbivores in the community, but was calculated on a standardised scale within each mesocosm (i.e., using the relative strength of interactions), we weighted community-level PAC values using the total herbivore biomass of the focal plant (for PACexerted) or the rest of the community (for PACreceived). We used these data to examine potential causes and consequences of PAC, asking whether: (1) exotic plants had greater PACexerted and lower PACreceived than native plants (prediction 3a in Table 1) (2) plants with greater PACreceived had lower total biomass and higher herbivore damage (prediction 3b) and (3) larger plants had greater PACexerted (prediction 3c). Hypotheses were tested using linear mixed models. Response variables were transformed as per Supplementary Table 26 and plant species and mesocosm nested within plant community were included in the models as random effects.

Finally, to explore whether plant–herbivore interactions contributed to the exotic plant dominance of plant communities (prediction 2b in Table 1), we asked whether the proportion of realised exotic biomass differed from the expected value based on the proportion of exotic plant species planted in the community. We calculated the proportion of exotic plant biomass per mesocosm and estimated the mean and 95% confidence interval for each level of proportion of exotic species planted in the community (i.e., 25, 50 and 75% exotic, but excluding communities planted with 0 and 100% exotic species) crossed with each level of the herbivore treatment. We then assessed whether 95% confidence intervals overlapped levels of the proportion of exotic plant species planted in the community (i.e., greater dominance by exotic plants than expected) and if 95% confidence intervals overlapped for +Herbivore vs. −Herbivore mesocosms within each level of proportion of exotics planted (i.e., herbivores altered the dominance of exotic plants). All analyses were performed in R 3.6.1 87 using the lme4 88 , emmeans 89 and bipartite 90 packages.

Reporting Summary

Further information on research design is available in the Nature Research Reporting Summary linked to this article.