Cult so affected by pest (6)

I believe the answer is:

locust

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'pest' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'cult so affected' is the wordplay.
'affected' indicates an anagram.
'cult'+'so'='cultso'
'cultso' anagrammed gives 'LOCUST'.

'by' is the link.

Can you help me to learn more?

(Other definitions for locust that I've seen before include "Voracious insect, travels in swarms" , "Migratory crop stripper" , "Voracious insect in dreaded swarms" , "Swarming grasshopper" , "Destructive creature" .)

I've seen this clue in The Mirror.

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