Which of the following insects is useful to humans?

Total silk production in India in $1990-91$ was

$A$ : Sericin is a gummy substance which is usually retained in case of silk till the yarn or fabric stage.
$R$ : Sericin gives protection during processing.

Silk is produced by

Mulberry, munga, oak and tussar, all the four varieties of silk are present in a single country. The country is

What is the larva of $Bombyx$ $mori$ called?