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Using Beneficial Nematodes for Grub Control and Japanese Beetles

Nematodes Biology fact sheet

Nematodes are microscopic, non-segmented worms which occur naturally in soil all over the world. Thousands of strains exist with different lifestyles. Beneficial nematodes attack only soil-dwelling insects and leave plants alone. Beneficial nematodes and the bacteria they spread are not known to be harmful to humans, animals, plants, earthworms or other non-target organisms, but they do aggressively pursue insects like grubs. When they sense the temperature and carbon dioxide emissions of soil borne insects, beneficial nematodes move toward their prey and enter the pest through its body openings. The nematodes carry an associated bacterium (Photorhabdus species) that kills insects fast (within 48 hours). Several generations of nematodes may live and breed within the dead pest; they emerge and seek more pests in the soil. Beneficial nematodes have been shown to be as much as 96% effective against Japanese beetle grubs in field studies. Although many species of beneficial nematodes are available, Heterorhabditis bacteriophora (Hb) nematodes are most effective against Japanese beetles, European chafers and other grubs that are lawn pests. They are more efficient than the Steinernema species. Hb nematodes work better because they are cruiser nematodes that burrow down in the soil searching for deep soil-dwelling pests. They also have a special "tooth" that helps them get into the grub.

Life Cycle

    Nematode Life Cycle Diagram
    Diagram courtesy of H. Kaya

    Steinernema and heterorhabditis have similar life histories. The non-feeding developmentally arrested infective juvenile seeks out insect hosts and initiates infections. When a host has been located, the nematodes penetrate into the insect body cavity, usually via natural body openings (mouth, anus, spiracles) or areas of thin cuticle. Once in the body cavity, a symbiotic bacterium (Xenorhabdus for steinernema, and heterorhabditis) is released from the nematode gut, which multiplies rapidly and causes rapid insect death. The nematodes feed upon the bacteria and liquefying host, and mature into adults. Steinernema infective juveniles may become males or females, where as heterorhabditis 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 days, and hundreds of thousands of new infective juveniles emerge in search of fresh hosts. 

    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 of one of classic mutualism. Nematode growth and reproduction depend upon conditions established in the host cadaver by the bacterium. The bacterium further 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. Conversely, the bacterium lacks invasive powers and is dependent upon the nematode to locate and penetrate suitable hosts. 

How often do I need to use biological control nematodes?

Contrary to what you may hear, in most cases biological control nematodes do not persist for a long time after they are applied. Most of these nematodes can live for only a few weeks at most without their host insect. Biological control nematodes occur naturally in most environments. They kill a few insects and help reduce insect epidemics. If they killed off all of their host insects, the nematodes would die off too. When we apply commercially available biological control nematodes, we are attempting to overload the natural system and kill many more insects than would be killed by nematodes naturally. If the treatment is successful, and most of the pest insects die, the nematode populations decline as well. Soon the natural balance is restored. When insect populations begin to build back up another nematode application is required.

 

 

The use of insect parasitic nematodes and other biological control agents to manage insect pests has grown in popularity. This is primarily due to the changing problems associated with pest control. For example, many pests have developed resistance to certain pesticides, new pests have arisen to replace those successfully controlled, the effectiveness of natural control agents (predators, parasites and pathogens) has been reduced by pesticide use, pesticides are no longer inexpensive to use, and there is increased concern about pesticide safety and environmental quality. These beneficial organisms can be an important component of an integrated pest management (IPM) program for ornamental crops and turf grass sites.

Before and after applying beneficial nematodes                               

What are beneficial nematodes?

Nematodes are morphologically, genetically and ecologically diverse organisms occupying more varied habitats than any other animal group except arthropods. These naturally occurring organisms are microscopic, unsegmented round worms that live in the soil and, depending on the species, infect plants and animals. The two nematode families Steinernemae and Heterorhabditidae, contain the insect parasitic nematode species. The most commonly used beneficial nematodes are Steinernema carpocapsae, S. feltiae, and Heterorhabditis bacteriophora. Nematodes that are endoparasites of insects attack a wide variety of agricultural pests.

The life cycle of beneficial nematodes consists of eggs, four larval stages and the adults. The third larval stage is the infective form of the nematode (IT). They search out susceptible hosts, primarily insect larvae, by detecting excretory products, carbon dioxide and temperature changes. Juvenile nematodes enter the insect host through the mouth, anus or breathing holes (spiracles). Heterorhabditid nematodes can also pierce through the insectís body wall. The juvenile form of the nematode carries Xenorhabdus sp. bacteria in their pharynx and intestine. Once the bacteria are introduced into the insect host, death of the host usually occurs in 24 to 48 hours.

As the bacteria enzymatically breaks down the internal structure of the insect, the Steinernemae develop into adult males and females which mate within the insect's body cavity. Heterorhabditids produce young through hermaphroditic females. This form of nematode has the sexual organs of both sexes. As the nematodes grow, they feed on the insect tissue that has been broken down by the bacteria. Once their development has reached the third juvenile stage, the nematodes exit the remains of the insect body.

Why are these organisms beneficial? Parasitic nematodes are beneficial for six reasons. First, they have such a wide host range that they can be used successfully on numerous insect pests. The nematodes' nonspecific development, which does not rely on specific host nutrients, allows them to infect a large number of insect species.

Second, nematodes kill their insect hosts within 48 hours. As mentioned earlier, this is due to enzymes produced by the Xenorhabdus bacteria. Third, nematodes can be grown on artificial media. This allows for commercial production which makes them a more available product.

Fourth, the infective stage is durable. The nematodes can stay viable up to 3 weeks when stored at the proper temperature. Refrigerated at 37o to 50o F. They can also tolerate being mixed with herbicides and fertilizers. Check nematode product label for compatibility. Also, the infective juveniles can live for some time without nourishment as they search for a host.

Fifth, there is no evidence of natural or acquired resistance to the Xenorhabdus bacteria. Though there is no insect immunity to the bacteria, some insects, particularly beneficial insects, are possibly less parasitized because nematodes are less likely to encounter Beneficial's which are often very active and escape nematode penetration by quickly moving away.

Finally, there is no evidence that parasitic nematodes or their symbiotic bacteria can develop in vertebrates. This makes nematode use for insect pest control safe and environmentally friendly. The United States Environmental Protection Agency (EPA) has ruled that nematodes are exempt from registration because they occur naturally and require no genetic modification by man.

How do you know which nematodes are beneficial and which ones are garden pests themselves? Scientists have spent years studying and identifying the life cycle of different types of nematodes. While there are nematodes that parasitize garden plants, the species being sold as beneficial nematodes have been thoroughly studied and their life-cycles are well understood. We can even buy specific species of beneficial nematodes for a special need. The most effective nematode for our garden problems is a combination of two species, Steinernema and Heterorhabditis.

Can nematodes hurt me or anything else? Studies have shown that these beneficial nematodes only target very specific pests and neither the nematode nor the toxins they produce can harm vertebrates. That leaves out all of us as well as our pets, birds, squirrels, etc. They don't hurt earthworms either.

What types of pest problems will beneficial nematodes help control? The specific type of nematode you buy for garden use targets any garden pest that has a larval stage in the soil. In our area, that would be cutworms, grubworms, many borers, root weevils, cabbage maggots, sod webworms and others. Many garden pests such as rose chafers have a larval stage in the soil, so they would be affected too.

What about iris borers? There has been some exciting work done on using beneficial nematodes to control iris borers. In a study done at the University of Maryland, beneficial nematodes applied by their guidelines did as good a job as any other treatment, including the now banned Cygon. For gardeners who want to avoid using harsh chemicals such as Cygon, beneficial nematodes may be a great alternative.

Steinernemae & Heterorhabditis

Nematodes are simple roundworms. Colorless, unsegmented, and lacking appendages, nematodes may be free-living, predaceous, or parasitic.  Species are beneficial in attacking insect pests, mostly sterilizing or otherwise debilitating their hosts. A very few cause insect death but these species tend to be difficult (e.g., tetradomatids) or expensive (e.g. mermithids) to mass produce, have narrow host specificity against pests of minor economic importance, possess modest virulence (e.g., sphaeruliids) or are otherwise poorly suited to exploit for pest control purposes. The only insect-parasitic nematodes possessing an optimal balance of biological control attributes are entomopathogenic or insecticidal nematodes in the genera Steinernema and Heterorhabditis. These multi-cellular metazoans occupy a biocontrol middle ground between microbial pathogens and predators/parasitoids, and are invariably lumped with pathogens, presumably because of their symbiotic relationship with bacteria.


Entomopathogenic nematodes are extraordinarily lethal to many important insect pests, yet are safe for plants and animals. This high degree of safety means that unlike chemicals, or even Bacillus thuringiensis, nematode applications do not require masks or other safety equipment; and re-entry time, residues, groundwater contamination, chemical trespass, and pollinators are not issues. Most biologicals require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, can kill insects within 24-48 hours. Dozens of different insect pests are susceptible to infection, yet no adverse effects have been shown against beneficial insects in field studies (Georgis et al., 1991; Akhurst and Smith, 2002). Nematodes are amenable to mass production and do not require specialized application equipment as they are compatible with standard  equipment, including various sprayers , backpack, pressurized, mist, electrostatic, fan, and aerial) and irrigation systems.


Hundreds of researchers representing more than forty countries are working to develop nematodes as biological insecticides. Nematodes have been marketed on every continent except Antarctica for control of insect pests in high-value horticulture, agriculture, and home and garden niche markets.

Description: http://www.biocontrol.entomology.cornell.edu/images/MAINlayout/REDbar_04.gif

Life Cycle

Steinernemae and heterorhabditids have similar life histories. The non-feeding, developmentally arrested infective juvenile seeks out insect hosts and initiates infections. When a host has been located, the nematodes penetrate into the insect body cavity, usually via natural body openings (mouth, anus, spiracles) or areas of thin cuticle. Once in the body cavity, a symbiotic bacterium (Xenorhabdus for steinernemae, Photorhabdus for heterorhabditids) is released from the nematode gut, which multiplies rapidly and causes rapid insect death. The nematodes feed upon the bacteria and liquefying host, and mature into adults. Steinernemae  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 days, and hundreds of thousands of new infective juveniles emerge in search of fresh hosts.  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. The bacterium further 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. Conversely, the bacterium lacks invasive powers and is dependent upon the nematode to locate and penetrate suitable hosts. 

Beneficial Nematodes -For Pest Insects

Beneficial nematodes seek out and kill all stages of harmful soil-dwelling insects. They can be used to control a broad range of soil-inhabiting insects and above-ground insects in their soil-inhabiting stage of life. More than 200 species of insect pests are susceptible to these insect predators.

They are a natural and effective alternative to chemical pesticides, and have no detrimental effect on non-target species such as ladybugs, earth worms and other helpful garden insects. Finally, there is no evidence that parasitic nematodes or their symbiotic bacteria can develop in vertebrates. This makes nematode use for insect pest control safe and environmentally friendly.

Beneficial nematodes can be applied anytime during the year when soil-dwelling insects are present .
10 Million nematodes, Garden Size: will treat up to 3,200 sq.ft
50 Million nematodes will treat up to 1/2 acre.
100 million nematodes will treat up to an acre.

 Steinernema feltiae

 Steinernema carpocapsae

 Heterorhabditis bacteriophora

Target Pests: Fly pests fungus gnats), Plant parasitic nematodes, Humpbacked flies, Fruit flies, Raspberry crown borer, Leaf miners, Cabbage maggot, Cucumber beetles, Shore flies, Black cutworm, Tobacco cutworm, White grubs, Beet armyworm, Onion maggot, Subterranean Termite.

Target Pests: Fleas, Codling moth, German cockroach, Asian cockroach, American cockroach, Fruit fly, Armyworm, Beet armyworm, Cucumber beetle, Artichoke plume moth, Cutworms, Sod webworm, Black cutworm, Mole cricket, Corn earworm, Cotton bollworm, Tobacco budworm, Leaf miners, Iris Borers.

Target Pests: Weevils, Beetle grubs, Japanese beetle, Masked chaffers, May/June beetles, Black vine weevil, various white grubs, Banana weevil, Bill bug, Colorado Potato beetle, Cucumber beetle, Sweet potato weevil, Asparagus beetle, Carrot weevil, Banana moth, Citrus root weevil group, Sugarcane stalk borer, Various tree and vine borers, Bagworms, Flea beetle, Flea.