2. DEFINE THE FOLOWING:
1.INSTAR
2.STADIUM
3.TYPES OF METAMORPHOSIS
a)HOLOMETABOLA
b)MEMIMETABOLA
c) PAUROMETABOLA
d)AMETABOLA
II. READ THE ARTICLE BELOW AND WRITE A ONE
PAGE REVIEW OF THE SAME
3. INSTAR
INSTAR is the name given to the developmental
stage of an arthropod between moults. For
example, after hatching from the egg and insect
is said to be in its first instar. When the insect
moults it is then a second instar and so on.
Instar can be used for insects undergoing
complete and incomplete metamorphosis.
4. STADUIM
Stadium—The duration of an instar. stadium is the time
between molts(shed old feathers, hair, or skin, or an old
shell, to make way for a new growth). The term larvae
(larva is singular) refers to the immature stages of
holometabolous insects. Nymph refers to the immature
stages of non-holometabolous insects. A holometabolous
insect larva turns into a pupa (pupae is plural) before it
molts into the adult.
5. TYPES OF METAMORPHOSIS
HOLOMETABOLA- Holometabolous (complete
metamorphosis) Typical holometabolous insect
groups are the Coleoptera (Beetles), Lepidoptera
(moths, butterflies and skippers) and Hymenoptera
(sawflies, wasps, ants and bees) and Diptera (flies).
All of these groups have a life cycle where the egg
hatches into a larva (e.g. a caterpillar, grub, maggot)
which goes through an inactive, pupa stage (e.g.
wrapped up like a cocoon) before emerging as an
adult (e.g. a butterfly, beetle, wasp).
6. MEMIMETABOLA
Hemimetabolous (incomplete metamorphosis)
Typical Memimetabolous insects are the Hemiptera (Scales,
Aphids, Whitefly, Cicadas, Leafhoppers and True Bugs),
Orthoptera (Grasshoppers and Crickets), Mantodea (Praying
Mantids), Blattodea (Cockroaches), Dermaptera (Earwigs) and
Odonata (Dragonflies and Damselflies). These groups go
through gradual changes as they turn into adults. Immature
forms of these insects are called nymphs and these gradually
increase in size and change form. As the insect grows, it sheds
its skin (called moulting). After each moult, the nymph looks a
bit different or a bit bigger. After a final moult, the full adult
form emerges
7. PAUROMETABOLA
Paurometabola is the process of gradual metamorphosis.
Paurometabolous is the type of growth that occurs in insects
such as cockroaches, which includes just three stages, i.e. egg,
nymph, and adult. It is called incomplete metamorphosis or
paurometabolous since it lacks the pupa stage. This implies that
through nymphal phases, there is growth from young to adult.
Nymphs are very much like adults. The nymph develops to
reach the adult form by moulting approximately 13 times. The
second-last nymphal stage shows the presence of wing pads,
which shows the presence of wings later in the last stage
(adult). Small adults resemble growth at immature stages and
live in the same habitat as adults and eat the same food.
8. AMETABOLOUS
An insect that undergoes slight or no metamorphosis. The young
look just like the adult. They also keep molting even after
becoming an adult, something the other kinds of insects don't do.
Hemimetabolous: An insect that undergoes incomplete
metamorphosis. The young look very similar to the adult.
9. The evolution of insect metamorphosis is one of the most important sagas
in animal history, transforming small, obscure soil arthropods into a
dominant terrestrial group that has profoundly shaped the evolution of
terrestrial life. The evolution of flight initiated the trajectory towards
metamorphosis, favoring enhanced differences between juvenile and adult
stages. The initial step modified postembryonic development, resulting in
the nymph–adult differences characteristic of hemimetabolous species. The
second step was to complete metamorphosis, holometaboly, and occurred
by profoundly altering embryogenesis to produce a larval stage, the nymph
becoming the pupa to accommodate the deferred development needed to
make the adult. These changing life history patterns were intimately linked
to two hormonal systems, the ecdysteroids and the juvenile hormones (JH),
which function in both embryonic and postembryonic domains and control
the stage-specifying genes Krüppel homolog 1 (Kr-h1), broad and E93. The
ecdysteroids induce and direct molting through the ecdysone
receptor (EcR), a nuclear hormone receptor with numerous targets
including a conserved transcription factor network, the ‘Ashburner cascade’,
which translates features of the ecdysteroid peak into the different phases
of the molt. With the evolution of metamorphosis, ecdysteroids acquired a
metamorphic function that exploited the repressor capacity of the
unliganded EcR, making it a hormone-controlled gateway for the tissue
development preceding metamorphosis. JH directs ecdysteroid action,
controlling Kr-h1 expression which in turn regulates the other stage-
specifying genes. JH appears in basal insect groups as their embryos shift
from growth and patterning to differentiation. As a major portion of
embryogenesis was deferred to postembryonic life with the evolution of
holometaboly, JH also acquired a potent role in regulating
postembryonic growth and development. Details of its involvement
in broad expression and E93 suppression have been modified as life cycles
became more complex and likely underlie some of the changes seen in the
shift from incomplete to complete metamorphosis.
