Caterpillar deceives corn plant into lowering defenses against it
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. 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.
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.
To test their hypothesis, researchers applied frass extract to the leaves of corn plants and compared the growth of fall armyworm caterpillars that fed on the leaves to the growth of caterpillars that fed on untreated leaves. They also measured the performance of a fungal pathogen in response to frass treatment of corn leaves. They inoculated the leaves with spores of a fungus that causes leaf blight in corn (Cochliobolus heterostrophus). 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.
Ref: Swayamjit Ray et al., 2015, J Chem Ecol
DOI 10.1007/s10886-015-0619-1
