An Ongoing War

At first glance, plants seem pretty harmless. I mean, what's this Honey Mesquite tree going to do to you if you try to cut it down? Fall on you I guess...

Image Courtesy of Encinalense

Apart from the obvious tactics like poison berries, plants have some really cool defense mechanisms to repel or 'take care of' predators. For instance, corn releases volatile chemical compounds when it is being eaten by worms. These compounds attract parasitic wasps that then lay eggs inside the worms. It's a win-win for the plant and the wasp. Other examples include essential oils that plants release when getting eaten. These oils can deter insects from the bad taste or smell, or even cause the plant to fortify its cell walls in order to make it more difficult to consume. That smell of freshly cut grass some people adore is actually a compound the plant releases to warn neighboring plants that danger is coming. Looking at it from that perspective, you're smelling the screams of your lawn.

Poor Things..
Image Courtesy of Pixabay.org

To combat all of these defense mechanisms, insects will have their own novel chemical compounds in their saliva. These compounds will suppress the defenses before the plant has the ability to activate them. Doctoral candidate Loren Rivera-Vega is investigating how a particular kind of caterpillar, the cabbage looper, avoids the defense systems of the plants it eats. The cabbage looper is quite unique in that it can eat a remarkable range of plants without triggering their defenses.

Cabbage Looper Caterpillar
Image Courtesy of Brittany Dodson

In order to determine what it is about the saliva that makes it unique, Rivera-Vega is letting the caterpillars eat different kinds of food sources, and then seeing what changed in their spit. After letting the insects feast on the different diets, she harvests the leaves and the caterpillar, and then does an analysis on the leaves to see what defense compounds were released by the plant. Then she slices up the caterpillars and harvests their salivary glands. The plants are then placed in a salt solution in order to extract the compounds for identification. She has found that the saliva does in fact change based on diet, increasing or decreasing the levels of certain proteins in order to better deal with the defenses of that particular plant.

Her next step is to better analyze the defense compounds put out by the different plants, in order to see if the caterpillar is really better dealing with the plants by changing their spit. This research could be very useful for agricultural purposes, as by better understanding the tactics that insects will take to prevent plant defenses, we can produce crops that are better suited to protect against insect damage. As farm land is getting more and more precious, the idea of efficiency in farming keeps getting more important.