Agriculture Reference
In-Depth Information
cases, may vary with the temperature, humidity, and availability and kinds of
food. The heaviest feeding generally occurs during the final two instars.
2.
No Metamorphosis
Some insects do not change except in size between hatching and reaching
the adult stage. The insect grows larger with each successive instar until it
reaches maturity. Examples are silverfish, firebrats, and springtails. The food
and habitats of the young (called nymphs) are similar to those of the adult.
3.
Gradual Metamorphosis
Insects in this group pass through three quite different stages of develop-
ment before reaching maturity: egg, nymph, and adult. The nymphs resemble
the adult in form, eat the same food, and live in the same environment. The
change of the body is gradual and the wings become fully developed only in
the adult stage. Examples are cockroaches, lice, termites, aphids, and scales.
4.
Incomplete Metamorphosis
The insects with incomplete metamorphosis also pass through three
stages of development: egg, naiad, and adult. The adult is similar to the
young, but the naiads are aquatic. Examples: include dragonflies, mayflies,
and sto nefli es. (See
Figure 3.2A.
)
5.
Complete Metamorphosis
The insects with complete metamorphosis pass through four stages of de-
velopment: egg, larva, pupa, and adult. The young, which may be called lar-
vae, caterpillars, maggots, or grubs, are entirely different from the adults.
They usually live in different situations and in many cases feed on different
foods than adults. Examples are the beetles, butterflies, flies, mosquitoes,
fleas, bees, and ants (see
Figure 3.2B
).
Larvae hatch from the egg. They grow larger by molting and passing
through one to several instar stages. Moth and butterfly larvae are called cat-
erpillars; some beetle larvae are called grubs; most fly larvae are called mag-
gots. Caterpillars often have legs; maggots are legless. Weevil grubs are
legless; other kinds of beetle larvae usually have three pairs of legs.
The pupa is a resting stage during which the larva changes into an adult
with legs, wings, antennae, and functional reproductive organs.
