Insects are developing immunity (10)
I believe the answer is:
resistance
'immunity' is the definition.
(I've seen this before)
'insects are developing' is the wordplay.
'developing' indicates an anagram.
'insects'+'are'='insectsare'
'insectsare' with letters rearranged gives 'RESISTANCE'.
(Other definitions for resistance that I've seen before include "Rebellious group" , "Violent opposition" , "Withstanding" , "French fighting group" , "underground movement" .)