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Tomato Plant Fun Fact - Cannibals in Your Garden

Timothy Boyer Ph.D.'s picture
Damaged Tomato Plant

There’s a lot of interesting science to be found in your garden. Here’s a tomato plant fun fact where you will see how tomato plants can make a caterpillar turn cannibal.

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In last week’s article we learned that growing tomatoes under climate-controlled fields may become a reality in the future due to a two-pronged attack by global warming and caterpillars. Tomato plants can handle either stressor individually; but together, not very well. So, in the absence of overly high temperatures, how do tomato plants ward off caterpillars and why is this significant?

According to a study published in 2017 in the journal Nature Ecology and Evolution, researchers found that like many plants, tomato plants are armed with natural defense mechanisms against predation by some insect species.

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One example is the release of chemicals like methyl jasmonate—a volatile plant hormone that has been described as being like a chemical scream given off by a plant when an insect begins to munch on its leaves. This volatile chemical can travel through the air and signal other nearby plants that a predator is about and is feeding. The signal received then induces other plants to invest in their own defenses—typically by producing chemicals that deter herbivores such as making their leaves unpalatable.

In the case of the tomato plant, it turns out that when its leaves are munched on by a caterpillar, its release of methyl jasmonate induces the offending caterpillars to turn on each other via cannibalism in preference to eating the tomato plant leaves.

“It often starts with one caterpillar biting another one in the rear, which then oozes. And it goes downhill from there,” says University of Wisconsin–Madison integrated biology Professor John Orrock, and lead author of the study.

Here’s a video showing Cannibal Caterpillars

https://www.youtube.com/watch?time_continue=6&v=NAQ-uWFHLGQ&feature=emb_logo

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In the study, researchers sprayed tomato plants with low, medium and high concentrations of methyl jasmonate, and then placed eight caterpillar larvae on each plant. The caterpillars were counted daily, and at the end of the experiment, the amount of plant material remaining from each treatment was determined by weighing.

Increased Methyl Jasmonte Exposure Increases Caterpillar Cannibalism

What the study revealed was that in the no-methyl jasmonate added control and in the low concentration methyl jasmonate test samples, the caterpillars ate the entire plant before turning to cannibalism. However, in the plants sprayed with the highest levels of methyl jasmonate, the tomato pants remained mostly intact while their caterpillar invaders turned to cannibalism much sooner than their counterparts did in the control and low-level methyl jasmonate test samples.

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In a second experiment, a single caterpillar larva was added to test containers holding either leaves that were not sprayed with methyl jasmonate and to test containers with leaves that had moderate amounts of methyl jasmonate sprayed on their surfaces. In addition, freshly frozen-and-thawed (weakened) caterpillars were added to all of the containers as tempting treats for the lone healthy caterpillar larva.

What occurred was that once again, in the presence of the methyl jasmonate, the caterpillars showed a preference for feeding on its own kind over the hormone-treated plant leaves.

“From the plant’s perspective, this is a pretty sweet outcome, turning herbivores on each other,” Orrock says. “Cannibals not only benefit the plant by eating herbivores, but cannibals also don’t have as much appetite for plant material, presumably because they’re already full from eating other caterpillars.”

In addition, the studies also showed that caterpillars placed with well-defended plants and no fresh caterpillar carcasses, ate less plant material and had lowered rates of growth.

A Possible Natural Pest Solution

The significance of this tomato plant fun fact is that it reveals the potential for plant scientists to develop a natural way of protecting plant crops from predators and thereby alleviating the need for pesticides in the produce we consume. Furthermore, by knowing that you might not need to douse your tomato garden with pesticides upon detecting caterpillars, you are forearmed with knowledge toward growing a healthier garden and possibly a new respect for tomato plants.

Don't Buy That Bottle of Caterpillar Cordyceps Mushroom Supplement Before Reading This

“…the research suggests that we may need to give plants a little more credit. Instead of being wallflowers who sit and wait for life to happen, plants respond to their environment with potent defenses, and these defenses make caterpillars more likely to eat other caterpillars,” stated Orrock in a news release produced by the University of Wisconsin-Madison.

If you enjoyed this fun fact about plant biology, let us know so that we can consider adding more articles of this type for your education and reading enjoyment.

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.

Image Source: Courtesy of Pixabay

References:

1. “Induced defenses in plants reduce herbivory by increasing cannibalism” John Orrock, Brian Connolly & Anthony Kitchen; Nat Ecol Evol 1, 1205–1207 (2017). https://doi.org/10.1038/s41559-017-0231-6.

2. “Plants under attack can turn hungry caterpillars into cannibals” July 10, 2017 by Kelly April Tyrrell, University of Wisconsin-Madison News.

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