The tot is a pest (4)
I believe the answer is:
slug
I believe this clue is a double definition.
'the tot' is the first definition.
(thesaurus)
'pest' is the second definition.
(I've seen this before)
'is a' acts as a link.
(Other definitions for slug that I've seen before include "Heavy blow for snail lacking shell" , "Slimy pest" , "ammunition?" , "Projectile fired from a gun" , "draught" .)