Sharing the Planet With Good and Bad Nematodes
Nathan Cobb, known as the father of nematology, once said, “In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.” Cobb even asserted that the species of an animal could be determined by examining this ghostly image of nematode parasites.
How could Cobb be so sure of the nematode’s omnipresence? Nematodes are the most abundant animal on the planet, making up four out of every five global creatures. The vast majority of nematodes are completely harmless. Many even play an essential role in the environment, such as free-living nematodes that make nutrients available for plants. However, harmful nematodes like hookworm are downright destructive. We’re here to break down the difference between good and bad nematodes. Since we’re vastly outnumbered by these microscopic worms, it helps to know which are working for and against us.
An Essential Part of the Soil Food Web
Most nematodes are considered free-living, meaning that they function at several trophic levels of the food web and act as prey and predator for other creatures. Free-living nematodes are some of nature’s most vital decomposers, recycling minerals and nutrients from bacteria, fungi and other substances back into the soil. These unsung heroes are especially good at mineralizing nitrogen. Nitrogen is an essential part of chlorophyll, which enables plants to conduct photosynthesis. Without free-living nematodes, fields would be filled with withered crops unable to convert sunlight into energy. Good nematodes like the free-living nematode are a vital component of soil microbial communities, which makes bad nematodes all the more difficult to deal with.
The Root of the Problem
Plant-parasitic nematodes don’t feed on bacteria, fungi and other microorganisms like free-living nematodes. Rather, they feed on plant roots by using their needle-like mouthparts, known as a stylet, to puncture plant cells and ingest plant fluids. As you can imagine, this process isn’t ideal for plant health. Unable to obtain water and nutrients through their damaged roots, affected plants become yellow, withered and stunted and eventually succumb to death.
One of the most destructive plant parasites is the root-knot nematode. Unlike other nematodes that feed on plants from the outside, root-knot nematodes are ectoparasites that enter and feed from within roots. This aptly named parasite injects hormones into plants that cause large, grotesque galls (knots) to form throughout root systems. Below the ground, root-knot nematodes feed off of the enlarged roots, while above the ground, the plant wilts and possibly dies. Plant-parasitic nematodes like the root-knot nematode cause an estimated $80-118 billion in damaged crops every year. However, the damage caused by nematodes that infect humans is far worse.
Intestinal nematodes, including hookworms, whipworms, pinworms and threadworms, are estimated to affect 3.5 billion people worldwide and cause approximately 125,000 deaths per year. Common symptoms of infection include diarrhea, abdominal pain and intestinal obstruction; however, nematode infections can result in far more serious conditions, such as anemia. The majority of infected people live in developing countries, where overcrowding, poor housing and a lack of sanitation lead to increased infection rates. Although intestinal nematodes thrive in tropical climates and developing countries, infections can also occur in developed countries like the United States.
Filarial nematodes are another cause of debilitating diseases. These thread-like worms are spread through insect bites and mature and mate in host tissues. Lymphatic filariasis (elephantiasis) and onchocerciasis (river blindness) are two tropical diseases caused by infection from these parasites. Elephantiasis occurs when filarial nematodes are transmitted via a mosquito bite and migrate to the lymphatic system. Upon death, filarial nematodes cause intense, painful inflammation in the limbs and groin, and those infected can face physical, mental, social and financial loses as a result.
Named for its prevalence near rapidly flowing water, river blindness is transmitted via the bite of a blackfly. From a single bite, filarial nematodes can generate over 1,000 juveniles a day. The juvenile nematodes then migrate to the skin and eyes, which can cause rashes, skin nodules and blindness. These diseases may seem far removed from everyday life, but they are a threat to millions of people across the world.
Living With Nematodes
For better or worse, we aren’t sharing our planet with nematodes. They’re sharing their planet with us. Out of the trillions and trillions of nematodes in the world, most are essential for processes that sustain plant life. However, there are other species of nematodes that strangle crops and infect humans. It is possible to share our planet with good and bad nematodes, and scientists are working tirelessly towards that goal.
From implementing biological controls to controlling the vectors of filarial nematodes, nematologists and entomologists are searching for novel, effective ways to manage nematodes. Despite the nematode’s incredible abundance, there is still very little known about these microscopic creatures and even less known about controlling their populations. If you are interested in learning about managing nematodes, both good and bad, apply to one of UF’s online entomology and nematology programs.