Predatory nematodes are of interest because of their role in regulating the populations of other organisms. They generally feed on smaller organisms like protozoa and other nematodes.
Thus they can help moderate population growth of bacterial- and fungal-feeding nematodes and protozoa, and help regulate populations of plant-parasitic nematodes. Insect-parasitic nematodes are species of bacterial-feeding nematodes that live in close association with specific species of bacteria; together, they can infect and kill a range of insect hosts.
The infective juvenile stage of insect-parasitic nematodes seeks out insect hosts to continue its development into adults. These bacteria multiply and overwhelm the immune response of the host insect, ultimately killing the host.
The nematodes feed on these bacteria, mature, and reproduce until all the resources within the insect host are consumed; then, infective juvenile nematodes escape the insect host's body and disperse in the soil to seek new hosts. Insect-parasitic nematodes are available commercially for use in inundative releases to manage the populations of a variety of insect pests. Most plant-parasitic nematodes feed on the roots of plants. Some species attach to the outside surface of plant roots Fig.
A relatively small number of important plant-parasitic nematode species are known to cause substantial economic damage in cropping systems around the world. The determination of tolerance limits or economic thresholds for plant-parasitic nematodes varies with many factors like species, plant tolerance, and soil type.
Because plant parasitic nematodes show varying degrees of host specificity, carefully designed crop rotations are usually a powerful tool for reducing nematode-associated yield losses.
Figure 3. White potato cyst nematode, Globodera pallida Stone Behrens, on plant roots. Cyst nematode females attach to root systems with their mouthparts to feed, and then their bodies swell into egg-filled cysts that can be visible to the naked eye. The proportions of the different feeding groups in the soil nematode community vary between systems and seasons, and they are influenced by a variety of factors, including crop and soil management practices Freckman and Ettema, and the presence and abundance of natural enemies.
A major function of soil nematodes is that they are biocontrol agents, meaning they can be used to eliminate disease causing nematodes and other organisms. This trait causes predatory nematodes to be a great resource in the battle against soil borne diseases.
This article was published by Michigan State University Extension. Are soil nematodes beneficial or harmful? There are also predatory nematodes that balance the population of other nematodes Nematodes are important nutrient mineralizers. Did you find this article useful? Please tell us why Submit. Beneficial nematodes feed on fungi, bacteria and other soil organisms, and help to suppress the activity of pest nematodes.
Background Nematodes are the most abundant multicellular animals on earth. How do beneficial nematodes help soil fertility? Nutrient cycling Nutrients, including nitrogen and phosphorus, stored in the bodies of bacteria, fungi, and other organisms are released when nematodes eat and digest them.
Insect and pest control Some predator nematodes attack and kill a range of pests such as borers, grubs, thrips and beetles with negligible effects on other organisms figure 1. Photo: Ontario Ministry of Agriculture Suppression of plant parasitic nematodes Since effective chemical control of pest nematodes is not practical in most farming situations, managing pest nematodes relies primarily on crop rotations using non-host varieties and resistant cultivars.
Photo: Nikki Seymour Soil high in organic matter also harbours many fungi that parasitise the females and eggs of pest nematodes, while others can trap and consume them figure 3. Figure 3: A nematode trapped by a fungal network.
Photo: Nikki Seymour Management effects on nematodes Agricultural cultivation tends to encourage an increase in plant parasitic nematodes over other species. Nematodes as indicators Analysis of the diversity and complexity of nematode communities in the soil is a valuable tool, which indicates soil biological fertility, or soil health.
Further reading and references This factsheet is adapted from the Soil Biology Basics information series. Related Soil Tests P. How would you like something worm-like, eight metres long and as thick as a garden hose wriggling Figure 1 around in your stomach? Well spare a thought for the sperm whale, because that is exactly what it has to put up with! A species of giant nematode Placentonema gigantissimum makes its home in the placenta of the sperm whale. That would be enough to make your stomach turn!
Humans can also be invaded by nematodes. The good news is that these are much smaller than Placentonema! The bad news is that these invaders can cause serious diseases. The nematode Wuchereria bancrofti for example affects over million people throughout tropical parts of the world. Other nematode parasites of humans are transmitted by eating meat that is not cooked sufficiently or through contact with faeces, or water contaminated with faeces, from humans or animals.
So wash your hands and watch what you eat and drink! Some species of nematodes live in the stomach of animals and prevent them from absorbing sufficient nutrients to grow properly. Figure 1.
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