The largest part of an insect leg is:

Other options and Explanation:
-Trochanter: This is the smallest segment of the leg, connecting the coxa to the femur.
-Tibia: The tibia is the next segment after the femur and is typically longer but thinner.
-Tarsus: The tarsus is the foot of the leg, composed of multiple segments and responsible for gripping surfaces.
-Pretarsus: The terminal part of the tarsus, including claws or pads.
-Coxa: The basal segment of the leg, attaching it to the thorax.