蛀 most commonly appears in the compound 蛀牙 (tooth decay / cavity) and in 蛀虫 (wood-boring insect; figuratively a corrupt person or parasite). The standalone verb 蛀 is less common than these compounds in everyday speech.
Bug radical on the left identifies the agent: 蛀 names the action of insects boring into wood, grain, or teeth. The radical groups it with the whole pest family - 蚊 mosquito, 蚂 ant, 蝇 fly.
Right side supplies the sound: zhǔ to zhù (tone shift). 主 also carries a faint hint of permanent residency - the boring insect takes up host residence inside its target. This metaphor extends naturally to 蛀牙 'tooth decay': the bug-master moving in.
