51I
t’s not easy to monitor electrical activ-
ity in an aphid. But it can be done with
wire and glue. This electrical penetration
graph technique involves gluing a wire onto
an aphid’s back so that the insect is still
able to walk around. When the animal is
allowed to eat a plant conducting an elec-
trical current, the resulting readout from
the plant can provide valuable information
about its feeding behavior. As an entomol-
ogy master’s student at Kansas StateUniversity in the mid-2000s, Joe Louis set
out to learn how to use the technique.
“He had to learn to apply the electron-
ics and the technical side of that, which
not many people have ever mastered,”
says John Ruberson, who worked at
Kansas State at the time and is now
head of the entomology department
at the University of Nebraska–Lincoln
(UNL), where Louis is an associate pro-
fessor. It might not have been obvious
to others why Louis needed to go to the
trouble, Ruberson explains, but mastering
the technique would pay off.
When a wired aphid pricks its needle-
like stylet into a plant conducting elec-
tricity, it completes an electrical circuit
and generates a voltage spike in the
readout from the wire. By using
RNAi to block a gene’s product in
insects and then employing their
technique to monitor the feed-
ing behavior, Louis was part of
a team that figured out that a
saliva protein in pea aphids
(Acyrthosiphon pisum) called
C002 is essential for the
insects to feed on fava bean
plants (PNAS, 105:9965–69,
2008). It was the first aphid
saliva protein identified.
After completing his mas-
ter’s in 2006, Louis stayed at
Kansas State to begin work-
ing toward a PhD with plant
biologist Jyoti Shah, using
the same electrical moni-
toring system in combina-
tion with molecular and bio-
chemical approaches to study
defenses the plant Arabidop-
sis thaliana deploys against
hungry insects. Working with
colleagues, they discovered
an Arabidopsis gene, MPL1,
that’s expressed in responseto aphid infestation and is critical to
the plant’s protection against the pests.
While the exact mechanism wasn’t clear,
the enzyme the gene codes for breaks
down lipids, and appeared to limit the
insects’ ability to reproduce, the research-
ers found (Plant J, 64:800–11, 2010). Shah
and Louis both moved to the University of
North Te x a s in 2007.
Louis was “a go-getter,” Shah says.
Rather than needing to be pushed to
publish his work, for example, he would
take the initiative to draft papers. “He
was ambitious.... Even at that early
stage of his career, he was quite inde-
pendent with how he did things,” Shah
recounts. “At the same time, he was
open to advice.”
After earning his PhD from the
University of North Texas, Louis went on
to a postdoc with Gary Felton and Dawn
Luthe at Pennsylvania State University
before starting his own lab at UNL. There,
he’s continued to delve into what he calls
the “tug-of-war” between pest and plant.
“We are trying to understand how plants
can recognize those insects... so that
they can rapidly and accurately activate... defenses,” he says. In a study published
last year, he worked with graduate stu-
dent Suresh Varsani and other colleagues
to identify a chemical called 12-oxo-
phytodienoic acid that is produced by
aphid-resistant maize. The acid enhances
the deposition of a protective polysaccha-
ride called callose along the inside of cell
walls, boosting the plant’s defenses (Plant
Physiol, 179:1402–15).
Ultimately, Louis hopes that findings
like these will lead to innovative ways to
protect crops from pests without harm-
ing the environment as today’s insecti-
cides do. “This kind of research helps to
[attain] a cleaner environment, and we
can reduce the usage of these pesticides
or chemical insecticides.”g
SCIENTIST TO WATC HJoe Louis: Insect Whisperer
© KATHY PLUNKETT PHOTOGRAPHY
51can reduce the usage of these pesticides51Associate professor of entomology and biochemistry, University of Nebraska–Lincoln, Age: 41BY SHAWNA WILLIAMS03.2020 | THE SCIENTIST 51