Story of Mulberry’s Secret Weapon and its specialized Silk-moth

img_20161126_093635by Hinal Kharva – As a part of our chemical ecology course at NCBS we had an opportunity to go on a nature walk with Dr. Uma Shankar from Gandhi Krishi Vigyan Kendra (GKVK). From my personal interaction with him, I could say he is one of the scientists who can develop a curiosity driven passion in almost every student.

In this session, he introduced us to one of the important plants of the silk moth’s life cycle (and thus most important in silk production), mulberries. We started our walk in mulberry plantations at the sericulture department (located within GKVK Campus). Interestingly, this is the only place in their campus where they don’t spray any insecticides or pesticides on these plants. The leaf of this plant is food for the silk moth (Bombyx mori), which are actually reared in the lab. In fact, due to heavy domestication, silk-moths are no longer available as a wild species! Here starts an interesting part. Insects other than the silk moth cannot feed on mulberry leaves. And do you know why? Mulberry leaves have a defense mechanism against insects, the production of latex (Milky liquid). Latex contains high concentrations of alkaloids, sugar-mimic glycosidase inhibitors. These inhibitors do not allow the further breakdown of sugars in most insects.

Studies have identified a latex protein called “MLX56”, which defends against several insects but not the silk moth. How does the silk moth deal with this latex? The silk moth has developed a strategy to avoid these glycosidase inhibitors, mainly by using an alternate fructosidase pathway. Fructosidase pathways are generally present in bacterial systems. The silk moth has evolved and adapted these pathways, and this is how it has become specialized on mulberry plant.

When we visited these plantation we did see hoppers, preying mantis, beetle, bugs and several other insects on the leaves but none of them were eating the leaves. This is one of the beautiful examples of plant-animal interactions that I learned during the nature walk. I am waiting for my next nature walk to learn new fascinating interactions and tell you some more interesting stories.

 

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