Animals have two ways to make sure that they leave
offspring in the world, so that their genes survive. One is to have few
children and care for each one intensely. The other is to have huge numbers of
offspring, so that even though many die enough survives. That is what insects
do. Most of those eggs, or the larvae they give birth to, will die in one way
or another, so there have to be many of them.
In most insects, life begins as an independent egg. This
type is reproduction is known as ovipary. Each egg is manufactured within the
female's genital system and is eventually released from her body through an
ovipositor, a tube-like, saw-like, or blade-like component of her external
genitalia. The egg-laying process is known as oviposition. Each insect species
produces eggs that are genetically unique and often physically distinctive as
well - spherical, oval, conical, sausage-shaped, barrel-shaped, or
torpedo-shaped. Yet regardless of size or shape, each egg is composed of only a
single living cell.
In most insects the egg is covered by a protective
"shell" of protein secreted before oviposition by accessory glands in
the female's reproductive system. This eggshell, called the chorion, is often
sculptured with microscopic grooves or ridges that may be visible only under
the high magnification of an electron microscope. The chorion is perforated by
microscopic pores that allow respiratory exchange of oxygen and carbon dioxide
with relatively little loss of water. The micropyle, a special opening near the
anterior end of the chorion, serves as a gateway for entry of sperm during
fertilization.
A female receives sperm from her male partner during the
act of mating. She can store that sperm for long periods of time in a special
part of her reproductive system, the spermatheca. As a developing egg moves
past the opening to the spermatheca, a few sperm are released onto its surface.
The sperm swim toward the micropyle - the first one to reach its destination
enters and injects its nucleus into the egg. The sperm nucleus quickly fuses
with the egg nucleus to form a one-celled embryo. This event is known as
fertilization. After the egg is fertilized, it undergoes a period of rapid
growth and development known as embryogenesis, literally the "embryo's
beginning".
Many insects pass the winter in the egg stage. Insect eggs are ideally suited
for withstanding the hardships of winter. The eggs have shells that are thick
and watertight. In many cases the eggs are covered with hairs, silk, or frothy
materials produced by the female before she died. These provide an extra degree
of protection by insulating the eggs. Most butterfly or moth caterpillars eat
their eggshell just after the hatching as they get maximum proteins out of eggshell.
But these “Baby Bugs” just crawling here without eating the eggshell.
Yuwaraj Gurjar.
Interesting read indeed! :)
ReplyDeleteAnother post with stunning pictures :)
ReplyDelete