It’s not easy to monitor electrical activity 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 electrical current, the resulting readout from the plant can provide valuable information about its feeding behavior. As an entomology master’s student at Kansas State University in the mid-2000s, Joe Louis set out to learn how to use the technique.
“He had to learn to apply the electronics 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 professor. 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 electricity, 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 feeding 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. It was the first aphid saliva protein identified.
After completing his master’s in 2006, Louis stayed at Kansas State to begin working toward a PhD with plant biologist Jyoti Shah, using the same electrical monitoring system in combination with molecular and biochemical approaches to study defenses the plant Arabidopsis thaliana deploys against hungry insects. Working with colleagues, they discovered an Arabidopsis gene, MPL1, that’s expressed in response to 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 researchers reported in 2010. Shah and Louis both moved to the University of North Texas 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 independent 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 student 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 polysaccharide called callose along the inside of cell walls, boosting the plant’s defenses.
Ultimately, Louis hopes that findings like these will lead to innovative ways to protect crops from pests without harming the environment as today’s insecticides do. “This kind of research helps to [attain] a cleaner environment, and we can reduce the usage of these pesticides or chemical insecticides.”