Cult so affected by insect (6)
I believe the answer is:
locust
'insect' is the definition.
(locust is a kind of insect)
'cult so affected' is the wordplay.
'affected' is an anagram indicator.
'cult'+'so'='cultso'
'cultso' anagrammed gives 'LOCUST'.
'by' is the link.
(Other definitions for locust that I've seen before include "Voracious African or Asian grasshopper" , "Dreaded grasshopper that swarms and devours" , "Swarming, devouring, insect" , "Sort of migratory grasshopper" , "Destructive tropical grasshopper" .)