Microscopic nematode worms can be a potent organic insecticide, killing crop-raiding bugs without harming plants or beneficial insects and without the environmental side effects of chemicals
This article originally appeared on January 14, 2010 in BYU News.
worms can be a potent organic insecticide, killing crop-raiding bugs
without harming plants or beneficial insects and without the
environmental side effects of chemicals. But when the worms are
mass-bred for agricultural purposes, they tend to, as Byron Adams says,
“wimp out,” and are not as deadly as their cousins that grow in the
The Brigham Young University biology professor and his
students analyzed the genetic changes in lab-raised worms that make them
less deadly to bugs. These results will help preserve the talents of
what Adams affectionately calls “natural-born killers.” The findings
also help us understand how to defeat parasites that harm beneficial
plants and animals and those that cause human disease.
reports its results in the new issue of BMC
Genomics. Graduate student Bishwo Adhikari is the lead author; two co-authors
who were undergraduates at the time are now pursuing Ph.D.s at Caltech
and the University of Wisconsin.
How the worms protect
When the worm, called H. bacteriophora finds
an insect in the soil, it crawls inside and, Adams says, “barfs up”
special bacteria that had hitched a ride with the worm. The bacteria
quickly kill the insect and spread, and the worm gobbles up the bacteria
and reproduces. The bacteria and baby worms eat what’s left of the bug,
and then head off together in search of another insect host.
and other insects, such as bees, are spared, and the worms are not
toxic to humans. The bacteria are only deadly when introduced inside the
insect, not when ingested, and can’t survive in soil or water. So they
are only a threat to the insects targeted by the worm, which include the
Japanese beetle, many species of weevils, the Colorado potato beetle,
cucumber beetles and many others. These pests can wreak havoc on citrus
trees, turfgrass, potatoes, and many other crops.
The worms occur
naturally in concentrations too small to be effective at eradicating
pests. So farmers can purchase bulk quantities of nematodes mass
produced in huge fermentation tanks and spread them through irrigation.
Producing deadly nematodes by the barrel is the problem.
worms wimp out
Previous research has shown that the
worms are less deadly to insects when grown away from their natural
habitat. After a few generations, they don’t reproduce or find hosts as
well, they have a tougher time tolerating heat and they aren’t as toxic
to the bugs they do find.
“We wanted to know the genetic
mechanisms that were responsible for these changes, so we did a series
of experiments to look at differences in gene expression between the
killers and the wimps,” said Adams.
The team examined all of the
expressed genes of an inbred line (wimps) of worms and their original
parental line (killers). They found differences in the expression of
1,185 genes, including those involved with metabolism, virulence and
“We show that even very small changes in the relative
expression of these genes can produce large changes in wimpiness,” Adams
Now scientists can take steps to improve the quality of
worms shipped to farmers. But that’s not what has Adams most excited
about this work.
Even broader application
research also shows that many of the genes involved in the killer/wimp
traits in these worms are unique to worms that are nasty parasites of
plants, humans and other animal friends,” Adams says.
these genes they identified play fundamental roles in host-parasite
interactions, such as virulence and the suppression of host defense
systems. That means the products of these genes could be promising
targets for pharmaceuticals.
Other interventions could prevent
disease by disrupting and altering the functions of these genes – taking
what was learned about how the bug-killing nematodes evolved to became
less deadly and leading harmful parasites down the same road.
contributions serve as launching pad
generated the “wimpy” line of worms for the study, which required
experiments to prove that the genetic deterioration came about because
of inbreeding and not other potential genetic causes. They are the first
authors on another paper about this that has been submitted for
John Chaston, featured here
for his work on nematodes in Antarctica, is now a National Science
Foundation fellow pursing a Ph.D. at the University of Wisconsin.
Dillman is now at Caltech, studying how genes influence behavior under
world renowned worm geneticist Paul Sternberg, also a co-author on the
paper. By the time he graduated from BYU, Dillman had presented research
at nine scientific conferences.
“Dr. Adams' attitude is unique
among undergraduate professors in that he encourages students to study
the primary literature and then to approach him with particular studies
or questions that they find interesting,” Dillman said. “He then helps
you turn that interest into a research program. Working for him was the
best thing that happened to me as an undergraduate.”
coauthors on the paper are: BYU’s Chin-Yo Lin, Ohio State’s Xiaodong Bai
and Parwinder Grewal, Michigan State’s Todd Ciche, the USDA’s David
Shapiro-Ilan; and Rutgers’ Anwar Bilgrami and Randy Gaugler.