Question

What is insect metamorphosis having larval instars called as?
a. Retrogressive metamorphosis
b. Complete metamorphosis
c. Incomplete metamorphosis
d. Super metamorphosis

Answer 1

Hint: In lower animals such as insects, the egg is laid which further hatches into a small individual. This organism grows and changes considerably from birth as it grows into an adult organism. These changes are abrupt and cause the organism to mature into an adult.

Complete answer:
Metamorphosis is the process through which an organism develops and matures through subsequent changes and matures into an adult. Metamorphosis occurs in several groups of insects and can be of three important types which are complete metamorphosis, incomplete metamorphosis and no metamorphosis.

In insects, growth and metamorphosis are related and controlled by hormonal control. Along the hormonal and neural-secretory cells are also involved in this process. The neurosecretory cells secrete a hormone known as the prothoracicotropic hormone (PTTH) which activates prothoracic glands. The PTTH gland produces a juvenile hormone which prevents development of adult characters.

In complete metamorphosis, the organism passes through four stages which are egg, larva, pupa and adult. It is also called holometabolous.

 In incomplete metamorphosis, the different stages are egg, nymph and the adult stage that is known as the imago. These types of metamorphosis have no pupal stage. It is also known as hemimetaboly.

In insects, the complete metamorphosis proceeds in repeated stages of growth and ecdysis or moulting. These stages are referred to as the instars. In complete metamorphosis, instars are referred to as the developmental stage of larval forms. The juvenile stage is close to resemblance to the adult stage. But the juvenile stage is smaller in size and they lack adult features such as genitalia and wings. In the early instars, the body is considerably smaller in size than the nymphs. However, the late instars show bud formation for wing development.

Retrogressive metamorphosis occurs in the urochordates in which an aquatic free-swimming larva with notochord metamorphosis or changes into a sedentary adult without notochord.

Hence, the correct answer is option (B).

Note: In insects, metamorphosis is an important feature in which a juvenile form passes through several moulting forms to give rise to the adult stages. This is controlled by the hormones. Larval instars are the stages of larval metamorphosis through complete metamorphosis.