Bill throttles the most acidic little pest (5)
I believe the answer is:
aphid
'little pest' is the definition.
(insect considered a pest)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for aphid that I've seen before include "Horticultural pest" , "Sap-sucking bug" , "Garden bug" , "Fly" , "Plant-louse" .)