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In a deception that likely has evolved over thousands of years, a caterpillar that feeds on corn leaves induces the plant to turn off its defenses against insect predators, allowing the caterpillar to eat more and grow faster, according to chemical ecologists in Penn State’s College of Agricultural Sciences.
The finding is one more revelation about the myriad of chemical signals that pass between plants and insects that scientists at Penn State and around the world have been discovering in recent years. In this case, the agent of deceit is the caterpillar’s feces, or “frass.”
Plants are under constant threat of attack from herbivorous insects. Nearly 400,000 plant-eating insect species are known to live on 300,000 plant species. When these herbivores feed on plants, they not only cause mechanical damage but often deposit substances that can manipulate the plant’s response to herbivory. These substances are analogous to the microbial-associated compounds that affect plant responses to pathogenic fungi or bacteria.
Fall armyworm larvae are voracious feeders on leaves in the confined whorls of corn plants, and by necessity the insects defecate nearby in the crevasses where the leaves meet the stalks. Copious amounts of
“It would be disadvantageous for the insect to deposit cues that could enhance plant defenses against it, so we investigated what chemical compounds in the
“It turns out that the caterpillar frass tricks the plant into sensing that it is being attacked by fungal pathogens and mounting a defense against them, thereby suppressing the plant’s defenses against herbivores. Plants cannot defend against both pathogens and insect attackers simultaneously — they must switch on either their pathway to defend against herbivores or their pathway to defend against pathogens.”
The research, recently published in the Journal of Chemical Ecology, may lead to the isolation of specific components of the
The elicitation of pathogen defenses by
To test their hypothesis, researchers applied
“The plant perceives that it is being attacked by a pathogen and not an insect, so it turns on its defenses against pathogens, leaving the caterpillar free to continue feeding on the plant. It is an ecological strategy that has been perfected over thousands of years of evolution,” Ray said.
The research was supported by the U.S. Department of Agriculture.
Source: Jeff Mulhollem, Penn State
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