Immature insect increased in each year (4)
I believe the answer is:
pupa
'immature insect' is the definition.
(I've seen this before)
'increased in each year' is the wordplay.
'increased' becomes 'up'.
'in' indicates putting letters inside.
'each year' becomes 'p.a.' (synonyms).
'up' going inside 'pa' is 'PUPA'.
(Other definitions for pupa that I've seen before include "Immature insect" , "Pre-adult insect or chrysalis" , "A chrysalis as of butterfly" , "not yet adult" , "Insect life stage between larva and adult" .)