Question

Where are Imaginal discs used?

Answer 1

An imaginal disc is one of the elements of a holometabolous insect larva that will become a part of the adult insect's exterior during the pupal metamorphosis. There are pairs of discs contained within the larva's body that will create the adult's wings, legs, antennae, and other structures, for example.
Many larval components are torn down during the pupal stage, and adult structures, including the discs, develop rapidly. Each disc's core component everts and elongates, eventually becoming the distal end of whatever appendage it's creating, such as a wing, leg, antenna, or other appendage.

Complete answer:
The imaginary discs can be used to investigate the role of regulatory proteins in cell proliferation control. Because aberrant cell proliferation in this disc is not deadly but produces eye abnormalities that are easily recognised in adults, it is particularly valuable for this purpose and in screens for mutants with cell-cycle problems. The eye disc's cells divide and differentiate in a synchronous wave called the morphogenetic furrow that runs across the disc during the third larval stage, as a result, a linear array of cells in well-defined stages of division and differentiation is generated.
The use of discs as a canvas allows researchers to investigate how cells and tissues respond to the acquisition or deletion of specific gene activities. The ability to use imaginal discs to aid future discoveries has not been questioned, indicating that future contributions in cell and developmental biology are likely.

Note:
The imaginal discs are named after the 'disc'-shaped structures that will give rise to the image. Imaginal discs are formed by groups of $10-50$ cells that separate from the embryo's epidermis. The majority of these primordia invaginate the larval epidermis and are only attached to it by a slender peripodial stalk.
Imaginal cells are tissue-specific progenitors that are assigned during embryogenesis and stay dormant throughout the embryonic and larval stages. The majority of Drosophila larval cells perish during metamorphosis. Imaginal cells give rise to pupal and adult tissues.