60 F

Davis, California

Monday, February 26, 2024

Nematodes: coming to an ecosystem near you

Nematode research is an exciting field of study in which there still remain many rich veins of research waiting to be tapped. There is a vast diversity among the world’s various nematode species, many of which have yet to be described, according to UC Davis professor and researcher Edwin Lewis. Lewis is a member of the department of nematology at UC Davis — which is in the process of merging with the department of entomology.

Recently, Lewis gave a public seminar addressed to students and faculty members of the Animal Behavior Graduate Group (ABGG). The seminar, titled “Infection Behaviors of Parasitic Nematodes: The Story of the Slithering Herd,” will be made viewable online on the entomology department webpage.

“There’s a great kind of mental image,” said James Carey, a UC Davis entomology professor, referring to an image of nematodes’ prevalence in plants and trees and all over the earth. “If you took everything away and just left nematodes in place, it would outline the world.”

Nematodes are often used as biological pest controls — killing crop pests such as weevils. Insect pests are more accurately targeted by nematodes compared to chemical pesticides making them an available tool for farmers.

During the seminar, Lewis explained that researchers haven’t yet discovered the method by which nematodes decide to infect a particular insect. A “risk prone” type nematode will usually infect an insect first and release bacteria into the insect’s system causing its immune system to be suppressed and the insect to eventually die. That insect then somehow becomes more attractive to the “risk averse” nematodes who decide, either individually or as a group, to also infect that same insect. This “leader-follower” behavior can also be found in other species, such as fish.

“It’s called a ‘decision,’ but it’s not a decision in the context that we think of with humans,” Lewis explained. “It’s not like me deciding between pepperoni and sausage pizzas. It’s not like a cognitive decision.”

“What is most intriguing about behavioral ecology work is that it illuminates fundamental motivations for different behaviors that can be extrapolated to larger organisms, even humans,” said Danica Maxwell, a graduate student majoring in entomology who does research with Lewis.

Larissa Conradt, a professor at the University of Sussex in the United Kingdom, has reported in her research that some animals are able to engage in “democratic” decision-making processes by communicating via ritualized movements, body postures and vocalizations. In a particular situation, when animals’ “voting” signals surpass certain intensity thresholds, behavioral mechanisms are triggered and the group acts together.

Such work points to the possibility that aspects of democratic behavior in humans are natural and that such behavior originated deep in our evolutionary past.

“Generations are long. They’re expensive to keep. There’s a ton of regulations,” said Lewis, referring to research on larger animals. “The diversity of [nematodes] allows you to ask the same types of questions as you can with any other group of animals.”

“Butterflies and zebras do the same things,” Lewis said. “They find food. They grow. They mate. They reproduce. So why have a lab full of zebras when you can have a lab full of caterpillars and find out the same thing?”

Currently, Lewis is working with graduate students who are doing research on nematodes and insects that involve pistachios, citrus or bees.

BRIAN RILEY can be reached at science@theaggie.org.


  1. I am a recently retired Research Entomologist, USDA-ARS Beltsville MD, and a new
    ‘Associate’ of the UC Davis Entomology Department. The talk by Dr. Lewis was particularly interesting to me because nematodes are important biocontrol agents, and I’m trying to use pheromones of predacious insects to manage these beneficials for biological control.

    Dr. Lewis did a great job of explaining the basic biology of parasitic nematode foraging and infection. I had no idea that these critters have one stage solely devoted to finding and attacking new hosts. To top it off, I appreciated the mathematical modeling analogy between the nematode infection process and those “other parasites”, Wall Street brokers. Who would have thought a talk on nematodes would include a discussion of “herd theory” based on the Wall Street “behavior”!?

    For me, much of the fun of this lecture was seeing the large turnout to such a seemingly esoteric lecture, and hearing the impressively high level of questioning. This lecture epitomized what I’ve hoped to become involved with at UC Davis.


    Dr. Jeffrey R. Aldrich
    Retired USDA-ARS Research Entomologist
    & Associate of the UC Davis Entomology Department


Please enter your comment!
Please enter your name here