How plants recognize the bugs that eat them

"The plants could clearly tell insects apart—they really seem to 'know' who's attacking," says Heidi Appel. (Credit: Janet Tarbox/Flickr)

Plants can tell exactly what type of insect is making a meal out of their leaves—and can change up their defenses to ward off an attack.

Identifying the genes behind this defensive response could allow plant breeders to target specific insect species when developing pest-resistant crops.

“It was no surprise that plants responded differently to having their leaves chewed by a caterpillar or sucked by an aphid,” says Heidi Appel, senior research scientist in plant sciences division and an investigator in the Bond Life Sciences Center at University of Missouri.

“What surprised us was how different plant responses were to each of the caterpillars and aphids. The plants could clearly tell insects apart—they really seem to ‘know’ who’s attacking.”

Caterpillars and aphids

The study published in the journal Frontiers in Plant Science shows that Arabidopsis, a small flowering plant related to cabbage and mustard, recognizes and responds differently to four insect species.

Two caterpillar species were placed on the plants and encouraged to chew on their leaves. Two species of aphids, or small insects that pierce plants with needle-like mouthparts, were also to attack the plants. The plants were then examined on the genetic level to gauge their responses.

The researchers saw that the plants responded differently to both species of caterpillars and both types of aphids and had different genetic responses in all four cases.

Additionally, insects caused changes on the signaling level that triggered genes to switch on and off helping defend plants against further attacks.

2,778 defense genes

“There are 28,000 genes in the plant, and we detected 2,778 genes responding to attacks depending on the type of insect,” says Jack Schultz, director of the Bond Life Sciences Center and a coauthor of the study.

“If you only look at a few of these genes, you get a very limited picture and possibly one that doesn’t represent what’s going on at all. Turning on defense genes only when needed is less costly to the plant because all of its defenses don’t have to be ‘on’ all the time.”


A sister study, led by Erin Rehrig, a doctoral student at the University of Missouri at the time of publication, showed that attacks by both caterpillars and beet armyworms increased plant hormones that trigger defense responses.

However, plants responded quicker and more strongly when fed on by the beet armyworm compared to the cabbage butterfly caterpillar indicating again that plants can tell the two insects apart.

“Among the genes changed when insects bite are ones that regulate processes like root growth, water use and other ecologically significant processes that plants carefully monitor and control,” Schultz says.

“Questions about the cost to the plant if the insect continues to eat would be an interesting follow-up study to explore these deeper genetic interactions.”

Researchers from Penn State and the University of British Columbia contributed to the study. The National Science Foundation funded the work.

Source: University of Missouri