Weaver ants: the living pesticide

Weaver ants: the living pesticide

Wearver ant

Wearer ant nest

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Sub family:	Formicinae
Tribe:	Oecophyllini
Genus:	Oecophylla Smith, 1860 (15-20 species).
Species:2 Diversity species	Oecophylla longinoda in blue,  Oecophylla smaragdina Fabricius, 1775 in red.

Introduction

Oecophylla is a genus of large arboreal ants of the African, Asian, and Australian tropics. The weaver ants belong to the ant genus Oecophylla (subfamily Formicinae) which contains two closely related living species: O. longinoda found in Sub-Saharan Africa and O. smaragdina found in southern India, southeast Asia, and Australia. They are provisionally placed in a tribe of their own, Oecophyllini. The weaver ant genus Oecophylla is known about 18-20 species from Africa to Asia in the tropics.

Weaver ants are best known for their remarkable nest construction. Using precise coordination, the weaver ants create very strong ant chains by linking legs to pull and bend leaves into desired tent like positions. The ants then use their own larvae to secrete a silk that is used to stitch leaves together to create a nest. They may have several nests dominating a few trees at once.

These conspicuous insects are weaver ants, creating nests by pulling living tree leaves together and securing them with silk produced by the ants' larvae.  Colonies are territorial, covering several trees and containing dozens of nests. 

They are very aggressive territorial ants and for over 1000 years they have often been used by farmers to control agricultural pests.

Oecophylla smaragdina workers have a vice like grip and tremendous strength. A worker has been recorded to support 100 times its own weight whilst standing upside down on glass!

Weaver ants are reddish ants that live in the tropical forests of Africa and India and many countries in southeast Asia. They are also found in Australia and the Solomon Islands. Their nests are found in forest trees.

A Queen of Oecophylla smaragdina that has shed its wings Weaver ant nest on a Mango tree nest in Kinnerasani Wildlife Sanctuary, Andhra Pradesh, India.

The life cycle

Weaver ants or Green ants (genus Oecophylla) are eusocial insects of the family Formicidae (order Hymenoptera).Weaver ants get their name from their habit of binding fresh leaves with silk to form their nests. Oecophylla weaver ants vary in color from reddish to yellowish brown dependent on the species. Oecophylla smaragdina found in Australia often have bright green gasters. In Vietnam they are called "kiến vàng" (yellow ants). The life cycle of the ant has four stages: egg, larva, pupa, and adult. 

Eggs of weaver ants

The queen ant starts the ants' nests/colonies. She flies and searches for mate/s. She can mate with one or a few males (one at a time) in the air, or on low vegetation, or on the ground. Once mated, she looks for a nest site, either on trees or open fields. Once situated, she gets rid of her wings, seals herself into a small chamber and lays a small batch of eggs. The eggs then hatch into larvae. The queen is located in one nest and her eggs are distributed to all the other nests where workers and soldier ants are found. She spends her life laying eggs. The workers are females and do the work in the nest. The larger ones are the soldiers who defend their colony. 

Fertilized eggs develop into females (workers and the queen) and unfertilized eggs into males. Female ants have 2 copies of each chromosome while males have one. 

Larvae and Pupa of weaver ants

The larvae feed on the unfertilized eggs as food which the queen lays especially for them. The first brood of workers are normally smaller since she can only provide a limited amount of food. Once the ants mature, they leave the nest and begin to look for preys. They bring food to the queen and their siblings so that later offspring are bigger. As the colony reaches maturity, it begins to produce the queens and males for the next generation. Males can remain in the nests for some months and most of them will die within a few days after leaving their nests. 

The larvae have special glands to produce lots of strong silks (adults do not produce silk). One colony is found over several nests that may be placed in various locations in a tree, or several trees, or in fields. 

The worker ants form a chain along the edge of the leaf and pull the edges together by shortening the chain by one ant at a time. Once the leaf edges are in place, each ant holds one larva in its mandibles and gently squeezes the larva to produce silk. The silk is used to glue the leaf edges together. 

Pupae are laid in nest with a short time before become adults.

Adult weaver ants

Adult weaver ants are reddish to brown in color and have 10-segmented antennae with 2-segmented clubs. Their eyes are relatively larger than those of other species of ants. They do not have stingers, but can give painful bites caused by the chemicals secreted from their abdomen. They make nests in trees or on leaves of legumes, or in bunds or levees of the fields. They have the most complex nests among ants' nests. They use fresh leaves to build nests . 

Queen 20-25mm, a strong ant, normally green and brown, monogyn (one queen per colony).

Workers 5-6mm. Mostly orange. Sometimes this species has green gasters. Minor workers tend to look after the brood and farm scale bugs for honey dew.

Major workers 8-10mm. Mostly orange, this ant has long strong legs, long flexible antennae and large mandibles. These ants forage, maintain and expand the nest.

A dealate queen of O. smaragdina having shed her wings after a mating flight.

O. smaragdina major workers inspecting and cleaning (allogrooming) another worker on its return to the nest.

Their lifecycle spans a period of 8 to 10 weeks.

The main characters

Diet

They farm scale bugs for their honeydew, and eat small insects.

Weaver Ants eat any small creatures that they can find, but they are particularly attracted to nectar. The weaver ants do not have a stinger, but inflict a painful bite which is aggravated by irritating chemicals secreted from their abdomen.

Like many other ant species, weaver ants prey on small insects and supplement their diet with carbohydrate-rich honeydew excreted by small insects (Hemiptera). 

Colony productivity  

Weaver ant colonies are founded by one or more mated females (queens). A queen lays her first clutch of eggs on a leaf and protects and feeds the larvae until they develop into mature workers. The workers then construct leaf nests and help rear new brood laid by the queen. As the number of workers increases, more nests are constructed and colony productivity and growth increase significantly.

Workers perform tasks that are essential to colony survival, including foraging, nest construction, and colony defense.

A colony may be dispersed over several nests which may be placed in various locations in a tree, or even span several trees. The queen is located in one nest and her eggs are distributed to the other nests.

Social organization

Weaver ants are Social insects. The exchange of information and modulation of worker behaviour that occur during worker-worker interactions are facilitated by the use of chemical and tactile communication signals. These signals are used primarily in the contexts of foraging and colony defense. Successful foragers lay down pheromone trails that help recruit other workers to new food sources. Pheromone trails are also used by patrollers to recruit workers against territorial intruders. Along with chemical signals, workers also use tactile communication signals such as attenation and body shaking to stimulate activity in signal recipients. Multimodal communication in Oecophylla weaver ants importantly contribute to colony self-organization.

Like many other ant species, Oecophylla workers exhibit social carrying behavior as part of the recruitment process, in which one worker will carry another worker in its mandibles and transport it to a location requiring attention.

Nest-building

Weaver ants' nests are among the most complex ants' nests. The ants choose living leaves to build nests. These provide well camouflaged protection from predators and the elements. To create their neat nest, chains of worker ants form along the edge and pull the edges together by shortening the chain by one ant at a time. Once the edges are in place, an ant holds one of their larvae in its mandibles and gently squeezes it so the larvae produces silk. The silk is used to glue the leaf edges together. The larvae have special glands to produce lots of strong silk. The adults do not produce silk.

The nest starts very simply. A group of worker ants finds a leaf that is soft and easy to bend. Several ants line up. Each holds an edge of a leaf in its mandibles and feet. Slowly, the ants pull the two leaf edges together. More and more workers join in. They link their feet and pull until the two leaf edges are nearly touching. Weaver ant nests begin small but can sometimes become so large they connect branches of neighboring trees.

A giant weaver ant nest may look like it is damaging the leaves and branches of a tree. But weaver ants actually protect the tree they are living in. The ants act like miniature bodyguards for the tree. They keep other animals like birds, reptiles, and other insects from living in the tree or eating it. Sharing the same resource or living space is called symbiosis.

Oecophylla weaver ants are known for their remarkable cooperative behaviour used in nest construction.The time required to construct a nest varies depending on leaf type and eventual size, but often a large nest can be built in significantly less than 24 hours. Although weaver ant's nests are strong and impermeable to water, new nests are continually being built by workers in large colonies to replace old dying nests and those damaged by storms.

Next, other worker ants carry larvae from the old nest and gently squeeze them between their mandibles. This causes the larvae to ooze a thin thread of silk. Then the workers get busy. Just like tiny tailors, they stitch the leaves together. In fact, another name for weaver ants is “tailor ants.” Treetop nests can become extremely large. Sometimes they even connect branches from two nearby trees.

Other features

Role in the habitat: Weaver ants are exploited by plants and animals. Some plants such as the Sea Hibiscus (Hibiscus tiliceaus) secrete nectar in their leaves to attract these ants, which in turn protect the plant from insect leaf eaters. The nasty bite of the ants also discourages larger herbivores.

Some other creatures also exploit the Weaver Ant's sweet tooth. Some caterpillars of the Lycaenidae and Noctuidae butterfly families secrete a honey dew that attracts these ants to protect them. Some of these caterpillars are more sinister and use their bribe to gain entry into the ant's nest and devour their larvae! Some jumping spiders look and more importantly, smell like ants, and in their disguise, enter the ant's nest to devour them and their larvae.

Miniature bodyguards for trees: A giant weaver ant nest may look like it is damaging the leaves and branches of a tree. But weaver ants actually protect the tree they are living in. The ants act like miniature bodyguards for the tree. They keep other animals like birds, reptiles, and other insects from living in the tree or eating it. Sharing the same resource or living space is called symbiosis.

A sweet deal: Weaver ants have a “sweet tooth” that some creatures use to their advantage. Certain butterfly caterpillars produce drops of a sweet liquid called honeydew. The honeydew attracts weaver ants to the caterpillars. The ants then protect the caterpillars.

Weaver ant workers take great care of the colony’s larvae. They feed them and are very careful when they move them. The larvae produce the special silk that holds the colony’s nest together.

The uses of weaver ants

Ant eaters

Weaver ant pupae are harvested and sold as food in markets in Thailand and the Philippines.The taste of the pupae has been described as creamy flavor. People also eat adult weaver ants. Their taste is described as lemony or creamy and sour. The Dayaks in Borneo mix adult ants with rice for extra texture and flavor. Weaver ants are fierce biters, so people who harvest them have to be extra careful!

Use as tradictional medicines

People who live near weaver ants sometimes use them as a type of medicine. The ants have a strong chemical in their bodies called formic acid. The ants use the formic acid to protect their nests. People have discovered that they can collect a few of the worker ants and crush them to make a special mixture. The mixture is then used to fight infections. This kind of medicine is called traditional medicine. Studying traditional medicines like this may help scientists find new methods to cure diseases.
The larvae and pupae are collected and processed into bird food, fish bait and in the production of traditional medicines in Thailand , Vietnam and Indonesia.

Use as a living insecticide

The ancient Chinese as early as in 300 AD, exploited the voracious appetite of these ants by using them to control insect pests in their citrus orchards. They use them to control insect pests in their citrus orchards. To do this, they first put a weaver ant nest in an orchard. Then, they place bamboo strips among the trees to serve as "ant bridges." These ant bridges encourage the ants to colonize all the trees. More fruit growers are now bringing back this traditional practice of using weaver ants for pest control. It is a cheaper way of dealing with insects that have developed resistance to chemical insecticides.

Large colonies of Oecophylla weaver ants consume significant amounts of food, and workers continuously kill a variety of arthropods (primarily insects) close to their nests. Insects are not only consumed by workers, but this protein source is necessary for brood development.

Because weaver ant workers hunt and kill insects that are potentially harmful plant pests, trees harboring weaver ants benefit from having decreased levels of herbivory. They have traditionally been used in biological control in Chinese and Southeast Asian citrus orchards from at least 400 AD. Many studies have shown the efficacy of using weaver ants as natural biocontrol agents against agricultural pests.

The use of weaver ants as biocontrol agents has especially been effective for fruit agriculture, particularly in Australia and southeast Asia. Fruit trees harboring weaver ants produce higher quality fruits, show less leaf damage by herbivores, and require fewer applications of synthetic pesticides.

Farmers in southeast Asia often build rope bridges between trees and orchards to actively recruit ants to unoccupied trees. Established colonies are often supplemented with food to promote faster growth and to deter emigration.

Today in plant production, Weaver ants are usud in biocontrol to kill many kinds of insects on plant fruit trees. Their type: generalist predator and their hosts: citrus stinkbug, leaf-feeding caterpillars, aphids, citrus leafminer, leafhoppers, plant hoppers, bugs, moths, adult black bugs, and small animals.
In Mekong delta of Vietnam, weaver ants are used as living pesticides to kill many insect species on fruit plant trees from hundreds of years to now a day.

Conservation and management

Weaver ants thrive well in undisturbed places and plenty of green leaves. Plant fruit trees or shrubs in or around your new citrus orchard however, banana, sapodilla, and papaya are less suitable.

Introduce only native weaver ants to the orchard when no black ants' species are present to ensure the establishment of a weaver ant colony. 

Provide them with food during the dry season such as dried fish and shrimp, cut into pieces that are small enough for the individual ant to carry. 

Put bamboo or wooden strips between trees to guide the ants to transfer from one tree to another for them to build new colonies in other trees. 

To expand weaver ants' colonies to other field crops, tie a rope to a tree where they live, to guide them to the areas you want them to colonize. Monitor regularly the ant colonies. Like other insects, ants are easily being killed by pesticide. 
                                                                                     Edited and posted by Hồ Đình Hải

References

1-http://www.myrmecos.net/formicinae/oecophylla.html

2-http://en.wikipedia.org/wiki/Oecophylla_smaragdina From Wikipedia.

3-http://en.wikipedia.org/wiki/Weaver_ant From Wikipedia.

4-http://www.antark.net/ant-species/weaver-ant-oecophylla-smaragdina.html

5-http://www.springerlink.com/content/l5n03712j4825517/

6-http://www.globio.org/glossopedia/article.aspx?art_id=11&art_nm=Weaver+Ants

7-http://www.new-ag.info/03-2/develop/dev02.html

8-http://www.naturia.per.sg/buloh/inverts/weaver_ants.htm

Nematodes: The parasites of insects

CROP PEST BIOCONTROL: Insect Parasitic Nematodes

Nematode Steinernema carpocapsae

Insects are killed by Nematodes

Introduction to Parasites

Etymology and technical words

-Etymology of the word “parasite”

First used in English 1539, the word parasite comes from the Medieval French parasite, from the Latin parasitus, the latinisation of the Greek (parasitos), "one who eats at the table of another" and that from (para), "beside, by (sitos), "wheat". Coined in English in 1611, the word parasitism comes from the Greek (para) +(sitismos) "feeding, fattening".

-Predators

In ecology, predation describes a biological interaction where a predator (an organism  that is hunting) feeds on its prey (the organism that is attacked). Predators may or may not kill their prey prior to feeding on them, but the act of predation often results in the death of its prey and the eventual absorption of the prey's tissue through consumption.

In the nature, crop pest insects are killed by many predators such as animals, spider and other insects.

-Parasitism

Parasitism is a type of non mutual relationship between organisms of different  species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasitereferred to organisms with lifestages that needed more than one host (e.g. Taenia solium). These are now called macroparasites (typically protozoa and helminths).

Parasitism can take the form of isolated cheating or exploitation among more generalized mutualistic interactions.

Parasitism is differentiated from the parasitoid relationship, though not sharply, by the fact that parasitoids generally kill or sterilise their hosts.

-Parasites

The word parasite now also refers to microparasites, which are typically smaller, such as viruses, bacteria, protozoas, nemayodes… and can be directly transmitted between hosts of the same species.

Unlike predators, parasites are generally much smaller than their host. Parasites show a high degree of specialization, and reproduce at a faster rate than their hosts. Classic examples of parasitism include interactions between vertebrate hosts and diverse animals such as tapeworms, flukes, the Plasmodium species, and fleas.

Parasitoids are organisms whose larval development occurs inside or on the surface of another organism, resulting in the death of the host. This means that the interaction between the parasitoid and the host is fundamentally different from that of a true parasite and shares some of the characteristics of predation.

Parasitoidism occurs in much the same variety of organisms that parasitism does.

Types of parasites

Parasites are small organisms that complete most or all of their life cycle within a host, and many are capable of a high degree of within-host replication. Not all parasites kill their hosts, but parasites almost always have negative effects on host survival and reproduction.

Parasites are classified based on their interactions with their hosts and on their life cycles.

Parasites that live on the surface of the host are called ectoparasites (e.g. some mites). Those that live inside the host are called endoparasites (including all parasitic worms). Endoparasites can exist in one of two forms: intercellular parasites (inhabiting spaces in the host’s body) or intracellular parasites (inhabiting cells in the host’s body). Intracellular parasites, such as protozoa, bacteria or viruses, tend to rely on a third organism, which is generally known as the carrier or vector.

The vector does the job of transmitting them to the host. An example of this interaction is the transmission of malaria, caused by a protozoan of the genus Plasmodium, to humans by the bite of an anopheline mosquito. Those parasites living in an intermediate position, being half-ectoparasites and half-endoparasites, are sometimes called mesoparasite.

-Social parasites take advantage of interactions between members of social organisms such as ants or termites.

-An epiparasite is one that feeds on another parasite. This relationship is also sometimes referred to as hyperparasitism, exemplified by a protozoan (the hyperparasite) living in the digestive tract of a flea living on a dog.

The parasites of insects

Many parasites and disease-causing pathogens are known to attack insects, including viruses, bacteria, fungi, protozoans, nematodes, and mites.

The infective stages of most insect parasites must be consumed orally, although some can invade though pores or membranous joints in the insect cuticle. Many researchers are currently exploring the role of parasites and infectious diseases in regulating insect population size (E.G. Faeth and Simberloff 1981, Bowers et al. 1993, Jaenike 1998).

Insects can be parasited by many organisms such as:

-Insect parasites (parasitoids) of insects:

Such as: Anaphes species, Aphidius species, Aphytis spp, Bracon cushmani, Citrus mealybug parasite, Cottony cushion scale parasite, Cottony cushion scale parasite, Elm leaf beetle parasite, Encarsia formosa, Encarsia formosa, Hyposoter exiguae, Lysiphlebus testaceipes, Tachinid flies, Trichogramma spp., Trioxys pallidus…

-Nematode parasites:

Such as: Steinernema: S. carpocapsae, S. feltiae, S. riobravis,Heterorhabditis bacteriophora, H.  megidis…

-Protozoan parasites:

Such as: many species of Sarcodina, Flagellata, Infosoria, Sporozoa (Coccidae , Neogregarinida , Cnidospora), Ophryocystis elektroscirrha and  Nosema species…

-Fungal parasites of insects:

Such as: Metarhizium anisopliae, Beauveria bassiana, B.tenella,Hirsutella thompsonii, Cordyceps militaris , Nomuraea rileyi, Paecilomyces farinosus, Lecanicillium lecanii, Coelomomyces spp, Paearia rileyi , Entomophthora sp.

-Bacterial parasits of insects:

Such as:

-Pseudomonas:Ps. aeruginosa, Ps. chlororaphis, Ps. reptilivora, Ps. septica, Ps. putida

-Proteus: Pr. vulguris, Pr. mirabilis, Pr. rettgeri.

-Clostridium: Cl. brevifaciens, Cl. malacosomae.

-Bacillus: B. popilliae, B. fribourgensis, B. lentimorbus, B. euloomarahae, B. cereus, B. Thuringiensis.

-And many others: Serratia marcescens,

-Viral parasites of insects:

Such as: NPV (nuclear polyhedrosis virus), GV (granulosis virus) and CPV (cytoplasmic polyhedrosis virus).

Use of Nematodes as Biological Insecticides

Nematodes are simple, colorless, unsegmented, round worms, lacking appendages. Nematodes may be free-living, predaceous, or parasitic, and many of the parasitic species cause important diseases of plants, animals, and humans.

The only insect parasitic nematodes possessing an optimal balance of biological control attributes are entomopathogenic (also referred to as "beneficial" or "insecticidal") nematodes in the genera Steinernema and Heterorhabditis.

Insect parasitic nematodes are extraordinarily lethal to many important soil insect pests, yet are safe for plants and animals. Most biologicals require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, kill insects in 24-48 hr. Dozens of different insect pests are susceptible to infection, yet no adverse effects have been shown against non-targets in field studies.

Biology

Steinernema and Heterorhabditis nematodes have similar life histories. The non-feeding infective juvenile seeks out insect hosts, especially in the soil environment. When a host has been located, the nematodes penetrate into the insect body, usually through natural body openings (mouth, anus, spiracles) or areas of thin cuticle. Once in the body cavity, a symbiotic bacterium (Xenorhabdus for steinernematids, Photorhabdus for heterorhabditids) is released from the nematode, which multiplies rapidly and causes rapid insect death. The nematodes feed upon the bacteria and liquefying insect, and mature into adults. Thus, entomopathogenic nematodes are a nematode-bacterium complex.

The nematode may appear as little more than a biological syringe for its bacterial partner, yet the relationship between these organisms is one of classic mutualism. Nematode growth and reproduction depend upon conditions established in the host cadaver by the bacterium. In turn, the bacterium contributes anti-immune proteins to assist the nematode in overcoming host defenses, and anti-microbials that suppress colonization of the cadaver by competing secondary invaders. Steinernematid infective juveniles may become males or females, whereas heterorhabditids develop into self-fertilizing hermaphrodites although subsequent generations within a host produce males and females as well. The life cycle is completed in a few weeks, and hundreds of thousands of new infective juveniles emerge in search of fresh insect hosts.

Entomopathogenic nematodes are remarkably versatile in being useful against many soil insect pests in diverse cropping systems, yet are clearly underutilized. Like other biological control agents, nematodes are constrained by being living organisms that require specific conditions to be effective. Unlike pesticides, desiccation or ultraviolet light rapidly inactivates insecticidal nematodes. Similarly, nematodes are effective within a narrower temperature range than chemicals, and are more impacted by suboptimal soil type, thatch depth, and irrigation frequency.

Nematode Appearance

Nematodes are formulated and applied as infective juveniles, the only free-living and therefore environmentally tolerant stage. Infective juveniles range from 0.4 to 1.1 mm in length and can be observed with a hand lens or microscope after separation from formulation materials. Disturbed nematodes move actively, however sedentary ambusher species (e.g. Steinernema carpocapsae, S. scapterisci) in water soon revert to a characteristic "J"-shaped resting position. Low temperature or oxygen levels will inhibit movement of even highly active cruiser species (e.g., S. glaseri, Heterorhabditis bacteriophora). In short, lack of movement is not always a sign of mortality; nematodes may have to be stimulated (e.g., probes, acetic acid, gentle heat) to move before assessing viability. Good quality nematodes tend to possess high lipid levels that provide a dense appearance, whereas nearly transparent nematodes are often active but possess low powers of infection.

Insects killed by most steinernematid nematodes become brownish-yellow, whereas insects killed by heterorhabditids become red and the tissue assumes a gummy consistency. A dim luminescence given off by insects freshly killed by heterorhabditids is a foolproof diagnostic for this genus (the symbiotic bacteria provide the luminescence). Black rotting indicate that the host was not killed by entomopathogenic species. Nematodes found within such cadavers tend to be free-living soil saprophages.    

Biological characteristics of key species

Steinernema carpocapsae: The most studied, available, and versatile of all entomopathogenic nematodes. Important attributes include ease of mass production and ability to formulate in a partially dried state that provides several months of room-temperature shelf-life. Particularly effective against lepidopterous larvae, including various webworms, cutworms, armyworms, girdlers, and wood-borers. This species is a classic sit-and-wait or "ambush" forager, standing on its tail in an upright position near the soil surface and attaching to passing hosts. Consequently, S. carpocapsae tends to be most effective when applied against highly mobile surface-adapted insects. Highly responsive to carbon dioxide once a host has been contacted, the spiracles are a key portal of host entry. It is most effective at temperatures ranging from 22 to 28°C.    

Steinernema feltiae: Attacks primarily immature flies, including mushroom flies, fungus gnats, and crane flies. This nematode is unique in maintaining infectivity at soil temperatures below 10°C. S. feltiae offers lower stability than other steinernematids.

Steinernema riobravis: This highly pathogenic species, isolated to date only from the Rio Grande Valley of Texas, possesses several novel features. Its effective host range runs across multiple insect orders. This versatility is likely due in part to its ability to exploit aspects of both ambusher and cruiser means of finding hosts. Trials have demonstrated its effectiveness against corn earworm and mole crickets. In Florida, tens of thousands of acres of citrus are treated annually for control of citrus root weevil with impressive results. This is a high temperature nematode, effective at killing insects at soil temperatures above 35°C. Only formulation improvements that impart increased stability are needed for this parasite to achieve its full potential.

It must also be noted that S. riobravis has been marketed for suppression of plant parasitic nematodes infesting turfgrass. There is substantial correlative data suggesting that some entomopathogenic nematodes may suppress plant species. Some skepticism may be healthy until this puzzling assertion can be fully confirmed by rigorously designed, multiple field experiments.

Steinernema scapterisci: The only entomopathogenic nematode to be used in a classical biological control program, S. scapterisci was isolated from Uruguay and first released in Florida in 1985 to suppress an introduced pest, mole crickets. The nematode become established and presently contributes to control. Steinernema scapterisci is highly specific to adult mole crickets. Its ambusher approach to finding insects is ideally suited to the turfgrass tunneling habits of its host. Commercially available since 1993, this nematode is also sold as a biological insecticide, where its excellent ability to persist and provide long-term control contributes to overall efficacy. Availability is severely restricted due to the small market niche this nematode occupies. This is aggravated by its specificity for a host that is very difficult to rear.

Heterorhabditis bacteriophora: Among the most important entomopathogenic nematodes, H. bacteriophora possesses considerable versatility, attacking lepidopterous and coleopterous insect larvae among other insects. This cruiser species appears most useful against root weevils, particularly black vine weevil where it has provided consistently excellent results in containerized soil. A warm temperature nematode,H. bacteriophora shows reduced control when soil drops below 20°C. Characteristic poor stability has limited the usefulness of this interesting nematode: shelf-life is problematic and most infective juveniles persist only a few days following field release.

Heterorhabditis megidis: First isolated in Ohio, this nematode is marketed in western Europe for control of black vine weevil and various other soil insects. Its large size, characteristic heterorhabditid instability, and dearth of field efficacy data limit its utility at present

Habitat

Steinernematid and heterorhabditid nematodes are exclusively soil organisms. They are found virtually everywhere, having been isolated from every inhabited continent from a wide range of ecologically diverse soil habitats including cultivated fields, forests, grasslands, deserts, and even ocean beaches.

Pests Attacked

Because the symbiotic bacterium kills insects so quickly, there is no intimate host-parasite relationship as is characteristic for other insect-parasitic nematodes. Consequently, entomopathogenic nematodes are lethal to an extraordinarily broad range of insect pests in the laboratory. Field host range is considerably more restricted, with some species being quite narrow in host specificity. When considered as a group of nearly 30 species, however, entomopathogenic nematodes are useful against a large number of insect pests, many of which are listed in the table below. As field research progresses and improved insect-nematode matches are made, this list is certain to expand. Regrettably, nematodes have yet to be found which are effective against several of the most important soil insects, including wireworms, grape phylloxera, fire ants, or corn rootworms.

The Common Current Use of Nematodes as Biological Insecticides

Berries	Root weevils	Heterorhabditis bacteriophora
Citrus	Root weevils	Steinernema riobravis
Cranberries	Root weevils	H. bacteriophora,  S. carpocapsae
	Cranberry girdler	S. carpocapsae
Mushrooms	Sciarids	S. feltiae
Ornamentals	Root weevils	H. bacteriophora, H. megidis
	Wood borers	S. carpocapsae, H. bacteriophora
	Fungus gnats	S. feltiae
Turf	Scarabs	H. bacteriophora
	Mole crickets	S. riobravis, S. scapterisci
	Billbugs	H. bacteriophora, S. carpocapsae
	Armyworm, Cutworm, Webworm	S. carpocapsae

Conservation

Conservation strategies are poorly developed and largely limited to avoiding applications onto sites where the nematodes are ill-adapted; for example, where immediate mortality is likely (e.g., exposed foliage) or where they are completely ineffective (e.g., aquatic habitats). Minimizing deleterious effects of the aboveground environment with a post-application rinse that washes infective juveniles into the soil is also a useful approach to increasing persistence and efficacy.

Native populations of insect parasitic nematodes are highly prevalent, but other than scattered reports of epizootics their impact on hosts populations is not well documented. This is largely attributable to the cryptic nature of soil insects. Consequently, guidelines for conserving native entomopathogenic nematodes have not been advanced.   

USE OF NEMATODES AS BIOLOGICAL INSECTICIDES

Pest Common name	Pest Scientific name	Key  Crop(s) targeted	Efficacious Nematodes
Artichoke plume moth	Platyptilia carduidactyla	Artichoke	Sc
Armyworms	Lepidoptera: Noctuidae	Vegetables	Sc, Sf, Sr
Banana moth	Opogona sachari	Ornamentals	Hb, Sc
Banana root borer	Cosmopolites sordidus	Banana	Sc, Sf, Sg
Billbug	Sphenophorus spp. (Coleoptera: Curculionidae)	Turf	Hb,Sc
Black cutworm	Agrotis ipsilon	Turf, vegetables	Sc
Black vine weevil	Otiorhynchus sulcatus	Berries, ornamentals	Hb, Hd, Hm, Hmeg, Sc, Sg
Borers	Synanthedon spp. and other sesiids	Fruit trees & ornamentals	Hb, Sc, Sf
Cat flea	Ctenocephalides felis	Home yard, turf	Sc
Citrus root weevil	Pachnaeus spp. (Coleoptera: Curculionidae	Citrus, ornamentals	Sr, Hb
Codling moth	Cydia pomonella	Pome fruit	Sc, Sf
Corn earworm	Helicoverpa zea	Vegetables	Sc, Sf, Sr
Corn rootworm	Diabrotica spp.	Vegetables	Hb, Sc
Cranberry girdler	Chrysoteuchia topiaria	Cranberries	Sc
Crane fly	Diptera: Tipulidae	Turf	Sc
Diaprepes root weevil	Diaprepes abbreviatus	Citrus, ornamentals	Hb, Sr
Fungus gnats	Diptera: Sciaridae	Mushrooms, greenhouse	Sf, Hb
Grape root borer	Vitacea polistiformis	Grapes	Hz, Hb
Iris borer	Macronoctua onusta	Iris	Hb, Sc
Large pine weevil	Hylobius albietis	Forest plantings	Hd, Sc
Leafminers	Liriomyza spp. (Diptera: Agromyzidae)	Vegetables, ornamentals	Sc, Sf
Mole crickets	Scapteriscus spp.	Turf	Sc, Sr, Scap
Navel orangeworm	Amyelois transitella	Nut and fruit trees	Sc
Plum curculio	Conotrachelus nenuphar	Fruit trees	Sr
Scarab grubs**	Coleoptera: Scarabaeidae	Turf, ornamentals	Hb, Sc, Sg, Ss, Hz
Shore flies	Scatella spp.	Ornamentals	Sc, Sf
Strawberry root weevil	Otiorhynchus ovatus	Berries	Hm
Small hive beetle	Aethina tumida	Bee hives	Yes (Hi, Sr)
Sweetpotato weevil	Cylas formicarius	Sweet potato	Hb, Sc, Sf

* At least one scientific study reported 75% suppression of these pests using the nematodes indicated in field or greenhouse experiments. Subsequent/other studies may reveal other nematodes that are virulent to these pests. Nematodes species used are abbreviated as follows: Hb=Heterorhabditis bacteriophora, Hd = H. downesi, Hi = H. indica, Hm= H. marelata, Hmeg = H. megidis, Hz = H. zealandica, Sc=Steinernema carpocapsae, Sf=S. feltiae, Sg=S. glaseri, Sk = S. kushidai, Sr=S. riobrave, Sscap=S. scapterisci, Ss = S. scarabaei. 

** Efficacy of various pest species within this group varies among nematode species.

Source:(Lewis and Grewal, 2005).

Commercial Availability

Of the nearly eighty steinernematid and heterorhabditid nematodes identified to date, at least twelve species have been commercialized. A list of some nematode producers and suppliers is provided below:

SOME COMMERCIAL PRODUCERS/SUPPLIERS*

A-1 Unique Insect Control  Telephone: 916-961-7945;  FAX: 916-967-7082	Andermatt Biocontrol AG  Switzerland. Hb, Hmeg, Sc, Sf.	ARBICO, Inc.  Telephone: 520-825-9785,  FAX: 520-825-2038 Hb, Sc, Sf.
Becker Underwood Telephone: 800-232-5907 Hb, Hmeg, Sc, Sf, Sk, Sr, Ss.	The Beneficial Insect Co. PO Box 471143 Telephone: 704-607-1631 Hb, Sc.	BioLogic Company  Springtown Road, P.O. Box 177 Willow Hill, PA 17271 Hb, Sc, Sf.
CropKing Inc. Telephone: 800/321-5656,  FAX: 330-302-4204 ;  FAX: 330-722-2616	E ~nema Germany. Telephone:+49-4307-8295-0;  FAX: +49-4307-8295-14 Hb, Sc, Sf	Gardens Alive! Lawrenceburg, IN 47025. Telephone: 513-354-1482
Gardener's Supply Company Telephone: 888-833-1412,  802-660-3500  FAX:800-551-6712 Hb, Sc (mixture)	Greenfire Inc.  Telephone: 530-895-8301,  800-895-8307;  FAX: 530-895-8317 Hb, Sc (mixture)	Green Spot, Ltd.  Telephone: 603-942-8925;  FAX 603-942-8932 Hb, Sc, Sf.
Harmony Farm Supply & Nursery Telephone:707-823-9125; FAX: 707-823-1734 Sc.	Hydro-Gardens, Inc.  Telephone: 888-693-0578, FAX: 719-495-2266	IPM Laboratories, Inc.  Locke, NY Telephone: 315-497-2063;  FAX: 315-497-3129
Koppert  (The Netherlands) Telephone:1-800- 928-8827 FAX: 734 641 3799 Hb, Hmeg, Sc, Sf.	M & R Durango, Inc.  Telephone: 800-526-4075;  FAX: 970-259-3857. Hb, Sc, Sf.	Natural Insect Control Canada, L0S 1S0. Telephone: 905-382-2904;  FAX: 905-382-4418.
Natural Pest Controls  8864 Little Creek Drive  Orangevale, CA 95662  Telephone: 916-726-0855	Nature's Control  Telephone: 541-245-6033;  FAX: 800-698-6250 Hb, Sc.	Peaceful Valley Farm Supply  Telephone: 888-784-1722,  530-272-4769
Rincon-Vitova Insectaries Inc.  Telephone: 805-643-5407,  800-248-2847;  FAX: 805-643-6267 Hb, Hi, Hmar, Sc, Sf.	Southeastern Insectaries, Inc. Telephone: 478-988-9412,  877-967-6777; FAX: 478-988-9413. Hb, Hi, Sc.	Territorial Seed Company  Telephone: 800-626-0866,  541-942-9547;  FAX: 888-657-3131.
Worm's Way Inc.  Telephone: 800-274-9676,  812-876-6450;  FAX: 800-466-0795.	Yardlover Telephone: 866-215-2230. Hb, Sc, Sf.	Gulf Coast Biotics United States ph: 1-800-524-1958 fax: 940-458-5188 marta@gulfcoastbiotics.com

References

1-http://oardc.osu.edu/nematodes/biologyecology.htm

2-http://www.monarchlab.org/lab/research/topics/Enemies/Default.aspx#Parasites

3-http://www.scribd.com/doc/49072252/15/Fungal-parasites-of-insects-and-nematodes

4-http://www.cdc.gov/parasites/about.html#

5-http://en.wikipedia.org/wiki/Parasitism From Wikipedia, the free encyclopedia

6-http://www.wormman.com/pd_nematodes.cfm

7-Nematodes www.biocontrol.entomology.cornell.edu/.../nematodes... 

8-Insect Parasitic Nematodes

9-Biocontrol Network - Beneficial Nematodes - Steinernema sp ...

10-Entomopathogenic nematode - Wikipedia, the free encyclopedia