MAY
1990

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

05-11-90

INSECT EGGS

Insect lives are frequently described in terms of a cycle:  egg to larva to pupa to adult and back to egg.  So the age-old paradox frequently asked of our fine feathered friend, the chicken, might also be relevant to insects.  Which came first:  the adult or the egg?

Every insect begins life as an egg.  Most insect eggs are laid by the adult before the embryo is fully developed.  Therefore, the egg doesn't hatch immediately.

Hatching time is usually short, normally within a few days.  Since insects don't incubate their eggs, hatching time is determined by the environmental temperature.  For instance, the eggs of the Oriental fruit moth will hatch in three to six days in warm weather, but may take up to 40 days in cooler weather.

Some insects hibernate in the egg stage.  In this case, the egg may not hatch for 6 to 10 months.  Grasshoppers and corn rootworms are such insects.  And eggs such of the walkingstick may remain unhatched for two years.

Fertilization is generally necessary to produce an insect egg that will hatch.  Some insect females have, however, eliminated the middleman in the reproductive process.  Insects that lay unfertilized eggs include some bees, ants, social wasps and many aphids.  In the social insects, unfertilized eggs develop into males while fertilized eggs become females.

Insect eggs come in various shapes.  Some are flat and scalelike.  Eggs of the European corn borer look like fish scales, half covering each other on the leaf of the corn.  Others look like miniature wine barrels placed neatly on a dock waiting export.  Some of the stinkbugs follow this pattern of egg placement.

The shell of the insect egg can be perfectly smooth.  However, some insect eggs are sculptured in striking markings that are the envy of human artists.  Generally, the thickness of the shell of the insect egg gives a hint of the environmental conditions it must face.  Eggs that hatch shortly after they are laid have thin shells.  Eggs that must endure the winter tend to have thick shells.  An exception is when the egg is laid in some protected place, such as in the soil or under the bark of a tree.

Some insects cover the egg mass with special materials.  Many moths cover the egg mass with hair from their bodies.  The female bagworm deposits eggs in the bag which served as her home.  The praying mantid secretes a brown, frothlike substance in which to enclose her eggs and attaches the mass to a twig or wire fence, where it remains for the winter.

While it is not possible to answer the question of which came first, it is true that the insect egg must survive if there are to be adult insects.  Diversity in the shape, size and placement of eggs suggests that insects have opted not to put all their eggs in the same basket!

 

Writer: Tom Turpin
Editor: Olivia Maddox