Pupal Stage

How does the pupation process work?

• Five days after the insect quits feeding, it undergoes pupation.
• To view the event, we keep the insect from burrowing into soil. The wandering insect is removed from the food, washed and dried and placed in a toilet paper roll.
• About 12 hours before pupation Manduca will develop a set of very brown bars on the thorax.
• You can see the split in the bars at the center line of the insect. Along this line, the insect will break the old cuticle and wriggle out over a period of several hours.

Look closely at the cast skins. Can you see the head capsules?

Can you see the true legs? These are exoskeletons of Manduca that have just molted. Manduca leaves behind the head capsule and the true legs from its old exoskeleton. All of this molting takes place underground in the pupal chamber.

• The larva, which would be underground, now begins to shrink and change shape from a long cylinder to a football shape.
• The football shape is formed because the muscles used in moving the prolegs and mandibles have been restructured or destroyed.
• If you look at the mandibles, you will see that they cannot move because the muscles that used to do that job have gone away.
• The body movements of the animal change radically. The insect can no longer walk but only rolls.
• This morphological change, which in nature occurs underground, allows the animal to form a cell with dimensions of about 3 inches long and 1 inch deep.
• The depth of the cell varies and it is unknown if the animal burrows deeper for winter metamorphosis than for summer metamorphosis.

What is the anatomy of the pupa?

• While molting the cuticle or exoskeleton of the pupa is transparent, and it is possible to see through to the blood (hemolymph).
• This transparency gradually decreases as the insect's cuticle begins to harden.
• Hardening (sclerotization) is a chemical process,this process creates a brown cuticle over the next 24 hours
• When the hardening process (sclerotization) is complete, Manduca will look a dark,reddish-color.
• It will gradually darken and, towards the end of the pupal period, it will become very dark and soft.
• The cuticle is hard enough that the insect can easily be picked up.
• The insect does not feed during this stage, but it does wiggle its abdomenif you touch it.
• The long handle-like structure on head is the proboscis, which folds back and forth several times inside the exoskeleton case. This will develop into the adult feeding tube.

What happens while Manduca is pupating?

• The eyes begin to form about 3 days after pupation and are complete by about day 12.
• The pigmentation of the wings can be seen starting about 15-18 days after pupation.
• The pupal cuticle begins to darken and thin about 3 days before adult emergence.
• The cuticle becomes almost parchment-like and seems to shrink or deform.

The pupa can be determined as male or female by looking at the ventral side of the abdomen in the last several segments. Males have several bumps while females have a very small protuberance.

• Manduca remains in the pupal stage depending upon the hours of light received by the larva.
• If a larva is exposed to 12 or less hours of light, (late summer conditions), the insect will go into the diapause phase and remain underground for 8 to 9 months.
• If the insect is exposed to 13 or more hours of light (early summer conditions), it will not go into diapause and will begin to develop immediately.
• This normally takes about one month to complete.