Insect is no longer on top of pudding (4)
I believe the answer is:
wasp
'insect' is the definition.
(wasp is a kind of insect)
'is no longer on top of pudding' is the wordplay.
'is no longer' becomes 'was' (I've seen this before).
'on top of' suggests taking the first letters (I've seen 'on top' mean this).
The first letter of 'pudding' is 'p'.
'was'+'p'='WASP'
(Other definitions for wasp that I've seen before include "spiteful person?" , "Striped insect" , "Social worker" , "Stingy type" , "type dominant across the pond" .)