The most common and most likely answer to this crossword clue is the 6 letter word INSTAR
I
N
S
T
A
R
Buddy explains!
The straight part
We know that "a stage in the development of an insect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a stage in the development of an insect = instar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INSTAR mean?
INSTAR noun- Any one of the several stages of postembryonic development which an arthropod undergoes, between molts, before it reaches sexual maturity.
- An arthropod at a specified one of these stages of development.
- (by extension) A stage in development.
- To stud or adorn with stars or other brilliants; to star.
- To make a star of; set as a star.