Altering Plant Defenses: Herbivore-Associated Molecular Patterns and Effector Arsenal of Chewing Herbivores
Molecular Plant Microbe Interactions
Plants and bugs have been battling an evolutionary arms race since the early Cambrian period some 500 million years ago. Plants evolve a useful defense strategy, bugs evolve a way around it, plants evolve further, bugs catch up again, and so it has continued and will continue until our sun supernovas. One fascinating leg of this arms race has to do with a plant's response to insect excrement, aka, frass.
Frass is similar to worm castings in that it contains nutrients that plants can use, as well as microbes that were part of the insect's gut flora, as well as other insect-produced compounds. The frass-associated microbes and compounds have been shown to cause plants to stimulate internal defense systems that make plants less palatable to hungry insects. The name given to these defense systems is Herbivore-Associated Molecular Patterns. The term "Patterns" is used to indicate the dynamic metabolic pathways that take place involving multiple bio-chemical compounds.
The research article this post links to is a review of scientific literature that identify the molecules, microbes, metabolomics, and modes of action that frass has been shown to affect. And it's not just frass that stimulates a plant's defense system, it's also an insect's saliva, eggs, chewing, even crawling. It makes perfect sense that a plant has senses to sense insect presence. The issue is, the pests also have senses that detect the defenses, thereby initiating further the development of the plant-pest arms race.
You can find insect frass here (Beetle Juice) that can be used as a fertilizer through soil amending, top dressing, or as part of a biologically rich compost tea. Thanks to all the scientists out there that bring this useful knowledge to light. Here's to evolving our way into a sustainable future.