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26 POTATO GROWER | FEBRUARY 2017 N ematodes are the most numerically abundant animals on earth. It is estimated that four out of every five animals is a nematode and that densities can exceed 1 million individuals per square meter. Nematodes, also called roundworms, can be free-living in soil or water, or parasites of animals or plants. Nematodes are found in an astonishing range of habitats, from the poles to the tropics, on mountains and in deserts, in lakes, rivers and in the ocean. In 1914, N.A. Cobb, the father of nematology in the United States, said, "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." Some nematodes feed only on plants and are referred to as plant parasitic nematodes. They may not appear as impressive as human parasites that cause river blindness, or filariasis in humans, but plant parasitic nematodes are responsible for an approximate 15 percent of crop loss per year worldwide, equating to some $78 billion. Plant-parasitic nematodes can come in many different shapes; most are slender and threadlike, but some are lemon-shaped, round or appear swollen. And, being less than 1 millimeter long, nematodes are almost invisible to the naked eye. They all share some common features. Plant-feeding nematodes have a sharp, needle-like structure in their mouth called a stylet, which acts like a small hypodermic needle the nematode uses to invade plant cells and suck out the cell contents. Most nematodes are subterranean—living below the soil surface—and have adapted to survive in potentially hostile soil environments. Nematodes have evolved many strategies to survive fluctuating soil temperature and moisture conditions, and to escape predation by other soil organisms such as fungi, bacteria or even voracious predatory nematodes. Some are able to survive the onset of extreme heat or cold, or drying of soil by entering a state of By Louise-Marie Dandurand, University of Idaho