Mandibles are reduced and functionless in
A.Cockroach Mandibles: Maxillae and labium cut away to show mandibles. The mandibles cut off pieces of food and crush them before they are swallowed. The other mouthparts help select the food and manipulate it between the jaws.
B. Mosquito- All but few adults lack mandible. Mouthparts are of the piercing-sucking type and form a long, needle-like proboscis.
C. Bed Bug- They have a small head with large antennae and large mandibles in their mouth.
D. Most butterflies and moths lack mandibles as they mainly feed on nectar from flowers. Queen bees have mandibles with sharp cutting teeth unlike worker bees, who have toothless jaws. Male dobsonflies have slender mandibles up to 2.5 cm long, half as long as the insect's main body.
So, the correct answer is “Butterfly”.