Ins and Outs of Beneficial Nematode Movement

By Sharon Durham
August 14, 2014

Tiny worms called nematodes don't move randomly through the soil, but instead find their way around by relying on electrical fields, according to U.S. Department of Agriculture (USDA) scientists.

A research team led by Agricultural Research Service (ARS) entomologist David Shapiro-Ilan and plant pathologist Clive Bock at the agency's Fruit and Tree Nut Research Laboratory in Byron, Georgia, found that the nematode Steinernema carpocapsae was attracted to an electrical current they applied to an agar dish. Based on that lab study, they concluded the worms rely on electricity, or electrical fields, to help them navigate in the soil. They then hypothesized that the nematodes may also use magnetic fields for the same purpose.

ARS is USDA's chief intramural scientific research agency, and this research supports the USDA priority of promoting international food security.

They tested their theory of magnetic fields by placing magnets on opposing sides of a petri dish containing agar and S. carpocapsae nematodes. One magnet was oriented toward the North Pole and the other magnet was oriented to the South Pole. The research team noted a directional response of the nematodes, with more of them moving toward the South Pole than the North.

This movement in response to magnetic fields, called magnetoreception, can be important in facilitating or enhancing foraging ability in various organisms. The research was published in the International Journal for Parasitology.

The scientists also looked at the movement of six different entomopathogenic (insect-killing) nematode species and found that their movement was not random. Instead, the worms moved together as a group. According to Shapiro-Ilan, this type of movement was like group behavior in other animals, such as a school of fish or a pack of wolves.

Based on these findings, the researchers contend that aggregated movement behavior may further contribute to a patchy distribution, or clumping, of natural or applied entomopathogenic nematode populations that is seen in crop fields. These findings were also published in the International Journal for Parasitology.

The studies have implications for understanding nematode foraging behavior and improving natural pest control tactics. Knowledge of how and why beneficial nematodes find their prey is essential to optimizing their use in biocontrol programs in the future.

Read more about this research in the August 2014 issue of Agricultural Research magazine.