Source : Webster's Revised Unabridged Dictionary (1913)

Bollworm \Boll"worm`\, n. (Zo["o]l.)
   The larva of a moth ({Heliothis armigera}) which devours the
   bolls or unripe pods of the cotton plant, often doing great
   damage to the crops.

Source : WordNet®

bollworm
     n : any of various moth caterpillars that destroy cotton bolls