A new pesticide could be engineered from an unlikely source: caterpillar frass, which is also known as poop. Penn State reported that a particular caterpillar, the armyworm, is able to bypass corn defenses and munch on the plant freely. How that is possible became a point of interest of a study and the conclusions look promising.
Plants are not passive creatures that simply allow herbivores to devour them though it may seem that way. Corn, for instance, knows when a caterpillar is munching through its leaves. It will then release enzymes which give a foul taste to discourage the herbivore. The armyworm, however, has an ingenious and sophisticated way of getting around this.
The corn plant has two defenses. It can defend against pathogens like those from fungi and from attacks from herbivores. However, one new detail scientists found is that the plant can only engage one defense at a time. The armyworm takes advantage of this weakness, Modern Farmer reported.
By depositing its frass in the plant near the stem, the plant then senses a fungal attack and mounts a defense. This leaves itself wide open to the hungry armyworms. The findings are now being fine-tuned to figure out what exactly in the frass causes this reaction.
For one, it is already known that when a caterpillar starts eating a plant that the plant knows from the attacker's mouth enzymes that it is being eaten. The compounds in the frass, however, have not yet been mapped out.
Dawn Luthe, a professor of plant stress biology, says, "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."
An organic and ecologically sustainable pesticide from caterpillar frass can enhance plant defenses against pathogens. It is also possible to incorporate frass proteins to the plant to make its native defenses even more effective.
