The Silkworm:
The mulberry silkworm otherwise known as the Bombyx mori, spins valuable silk fibres making it one of the most beneficial insect to mankind. A rang of chemicals in the leaf are concerned with very specific feeding behavior. The substances can be divided into three groups: olfactory attractants, biting factors, and swallowing factors. Each group has a specific role in the insect feeding response. Contributing to the smell of the mulberry leaf, the insect larvae use their oral sense receptors to feed on the mulberry leaf. With the biting factors the three essential dietary requirements, sucrose, inositol, and sitosterol, all must act as general feeding stimulants to most insects. Two other substances, morin and isoquercitrin, combined with the essential oils in the leaf provides the specific basis for the attraction of the silkworm to its favoured food source. The final stage of the silkworm feeding is the act of swallowing and here relatively common chemicals provides the necessary stimulus. Silicate and phosphate are cellulose that are richly present in the cell wall of the mulberry leaves. These substances provide the necessary “bulk” to the insect alimentary canal in just the same way as “roughage” is a needed requirement in mammalian diets.
Table of Chemical factors of mulberry leaves associated with silkworm feeding
|
Attractants |
Biting factors |
Swallowing factors |
|
ESSENTIAL OILS: Citral Terpinyl acetate Linalyl acetate Linalol B, y-Hexenol |
FLAVONOIDS: Isoquercitrin Morin TEROENOID: Sitosterol SUGARS: Sucrose Inositol |
INORGANIC ELEMENTS: Silicate Phosphate CELL WALL COMPONENT: Cellulose
|
Silk, which is well known since the ancient times as a
natural textile fibre, has a predominantly proteinic matrix. In fact it is
constituted of preteins like the firoin, which represents a prevailing fraction
of the fibre (70-80%), and the sericin which represents the remaining 20-30%. A
moist substance, fibroin, is manufactured in two silk glands located on the
underside of the larva's body; mixed with a small amount of wax, it is emitted
from an orifice called the spinneret, in the lip of the larva. The fibroin
dries quickly in the air, hardening into a half-mile-long thread of silk that
makes up the cocoon. While sericin is a fine, horny, translucent, yellowish
fiber produced by the silkworm in
making its cocoon .Sericin belongs to a family of proteins having high content
of hydroxyl amino acids. The high polarity differentiates the sericin from the
fibroin and it allows the extraction of the silk from the fibre.
Interesting Behaviors
Silkworms have been used by researchers to study pheromones or sexual
attractant substances. The pheromones are released by female moths and the
males detect the chemicals with olfactory hairs on their antennae. This allows
the male to find the female for mating. The male antennae are made of many
small hairs to increase the chances of picking up small amounts of the
pheromones over long distances.
References:
http://insected.arizona.edu/silkinfo.htm
http://encyclopedia.com/html/s1/silkworm.asp
Harbone, J. B. Introduction to the Ecological Biochemistry. New York: Academic Press Inc., 1977.