Form of insect life in Papua New Guinea finally disappearing (4)

I believe the answer is:

pupa

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'form of insect' is the definition.
'pupa' can be an answer for 'insect' (pupa is a kind of insect). I am unsure of the 'form of' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pupa that I've seen before include "Immature insect" , "Developing butterfly" , "creepy-crawly" , "appearance of immaturity" , "A chrysalis as of butterfly" .)

I've seen this clue in The Independent.

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