Caterpillars attracted to plant SOS

Date: July 1, 2013

Source: Frontiers

Summary:

Plants that emit an airborne distress signal in response to herbivory may actually attract more enemies, according to a new study.

This image shows the detail of the four-arm olfactometer setup for S. littoralis larval behavior.

Credit: Drawing by Thomas Degen (www.thomas-degen.ch)

Plants that emit an airborne distress signal in response to herbivory may actually attract more enemies, according to a new study published in the open-access journal Frontiers in Plant Science .

A team of researchers from Switzerland found that the odor released by maize plants under attack by insects attract not only parasitic wasps, which prey on herbivorous insects, but also caterpillars of the Egyptian cotton leafworm moth Spodoptera littoralis, a species that feeds on maize leaves.

When damaged, many plants release hydrocarbons called volatile organic compounds, similar to the compounds that cause the characteristic smell of freshly cut grass. These volatile organic compounds are known to be attractive to parasitoid wasps that lay their eggs inside other insects, killing them. Plants appear to use this strategy to fight back against herbivorous insects by calling for their enemies' enemies. In contrast, herbivorous insects tend to avoid the herbivore-induced volatile organic compounds.

"Adult moths and butterflies avoid food plants that are under attack by conspecifics. This seems adaptive, because it reduces both competition and the risk of predation by parasitoids. But we found that S. littoralis caterpillars are actually attracted to the odor of damaged maize plants, even when this odor is mimicked in the laboratory with a mix of synthetic compounds," said Prof. Ted Turlings, an author of the study and head of the Laboratory for Fundamental and Applied Research in Chemical Ecology Institute of Biology at the University of Neuchâtel, Switzerland.

To determine what kind of odors the caterpillars preferred, the researchers let the caterpillars chose among several odors by placing them in an olfactometer, a device consisting of four tubes connected to a central chamber, with each tube introducing an airflow carrying a different odor. The caterpillars were more than twice as likely to crawl towards the odor from maize plants under attack by conspecifics than towards undamaged plants, especially if the damage was recent and the caterpillars had already fed on maize.

So what might be the advantage to the caterpillars of moving towards plants that are already infested? "When S. littoraliscaterpillars drop from a plant they are highly vulnerable to predators and pathogens in the soil, as well as to starvation. The advantage seems to be that fallen caterpillars can quickly rediscover the plant on which they fed. The caterpillars feed less and move more when exposed to high concentrations of the volatiles. By moving away from freshly damaged sites, they can minimize risk of predation and avoid competition," explained Prof. Turling.

Turlings and colleagues propose that hungry S. littoralis caterpillars do the best of a bad job by moving towards volatile organic compounds released by damaged maize plants. On these plants the competition may be more intense, but at least the caterpillars are assured of a suitable plant. Adult moths, on the other hand, are much more mobile and take little risk exploring the environment to discover the best food source -- so they avoid maize that is already under attack.

Story Source:

Materials provided by Frontiers. Note: Content may be edited for style and length.

Journal Reference:

Georg E. von Mérey, Nathalie Veyrat, Marco D'Alessandro, Ted C. J. Turlings. Herbivore-induced maize leaf volatiles affect attraction and feeding behavior of Spodoptera littoralis caterpillars. Frontiers in Plant Science, 2013; 4 DOI: 10.3389/fpls.2013.00209

Cite This Page:

Frontiers. "Caterpillars attracted to plant SOS." ScienceDaily. ScienceDaily, 1 July 2013. <www.sciencedaily.com/releases/2013/07/130701135820.htm>.

Harm and response: Plants recognize and respond to different insects

Date: February 13, 2015

Source: University of Missouri-Columbia

Summary:

In one of the broadest studies of its kind, scientists recently looked at all plant genes and their response to the enemy. Their results showed that the model Arabidopsis plant recognizes and responds differently to four insect species. The insects cause changes on a transcriptional level, triggering proteins that switch on and off plant genes to help defend against more attacks.

University of Missouri Bond Life Sciences Center's Jack Schultz and Heidi Appel hold model Arabidopsis plants used in many of their experiments.

Credit: Roger Meissen/Bond LSC

We often think of damage on a surface level.

But for plants, much of the important response to an insect bite takes place out of sight. Over minutes and hours, particular plant genes are turned on and off to fight back, translating into changes in its defenses.

In one of the broadest studies of its kind, scientists at the University of Missouri Bond Life Sciences Center recently looked at all plant genes and their response to the enemy.

"There are 28,000 genes in the plant, and we detected 2,778 genes responding, depending on the type of insect," said Jack Schultz, Bond LSC director and study co-author. "Imagine 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. This is by far the most comprehensive study of its type, allowing scientists to draw conclusions and get it right."

Their results showed that the model Arabidopsis plant recognizes and responds differently to four insect species. The insects cause changes on a transcriptional level, triggering proteins that switch on and off plant genes to help defend against more attacks.

The difference in the insect

"It was no surprise that the plant responded differently to having its leaves chewed by a caterpillar or pierced by an aphid's needle-like mouthparts," said Heidi Appel, Bond LSC Investigator and lead author of the study. "But we were amazed that the plant responded so differently to insects that feed in the same way."

Plants fed on by caterpillars -- cabbage butterfly and beet armyworms -- shared less than a quarter of their changes in gene expression. Likewise, plants fed on by the two species of aphids shared less than 10 percent of their changes in gene expression.

The plant responses to caterpillars were also very different than the plant response to mechanical wounding, sharing only about 10 percent of their gene expression changes. The overlap in plant gene responses between caterpillar and aphid treatments was also only 10 percent.

"The important thing is plants can tell the insects apart and respond in significantly different ways," Schultz said. "And that's more than most people give plants credit for."

A sister study explored this phenomena further, led by former MU doctoral student Erin Rehrig.

It showed feeding of both caterpillars increased jasmonate and ethylene -- well-known plant hormones that mediate defense responses. However, plants responded quicker and more strongly when fed on by the beet armyworm than by the cabbage butterfly caterpillar in most cases, indicating again that the plant can tell the two caterpillars apart.

The result is that the plant turns defense genes on earlier for beet armyworm.

In ecological terms, a quick defense response means the caterpillar won't hang around very long and will move on to a different meal source.

More questions

A study this large has potential to open up a world of questions begging for answers.

"Among the genes changed when insects bite are ones that regulate processes like root growth, water use and other ecologically significant process that plants carefully monitor and control," Schultz said. "Questions about the cost to the plant if the insect continues to eat would be an interesting follow-up study for doctoral students to explore these deeper genetic interactions."

Story Source:

Materials provided by University of Missouri-Columbia. Original written by Roger Meissen. Note: Content may be edited for style and length.

Journal Reference:

Heidi M. Appel, Howard Fescemyer, Juergen Ehlting, David Weston, Erin Rehrig, Trupti Joshi, Dong Xu, Joerg Bohlmann, Jack Schultz. Transcriptional responses of Arabidopsis thaliana to chewing and sucking insect herbivores. Frontiers in Plant Science, 2014; 5 DOI:10.3389/fpls.2014.00565

Cite This Page:

University of Missouri-Columbia. "Harm and response: Plants recognize and respond to different insects." ScienceDaily. ScienceDaily, 13 February 2015. <www.sciencedaily.com/releases/2015/02/150213104721.htm>.