Insect in a pickle? Most delightful! (6)
I believe the answer is:
nicest
'most delightful' is the definition.
'insect in a pickle?' is the wordplay.
'in a pickle?' indicates anagramming the letters (UK expression meaning 'in trouble or difficulty').
'insect' is an anagram of 'NICEST'.
(Other definitions for nicest that I've seen before include "Most attractive" , "most appetising" , "Best" , "Insect (anag)" , "Sin etc (anag)" .)