Unable to complete metamorphosis

A gene named Broad is found in caterpillars and, is essential for the change from larva to pupa to complete the metamorphosis. If a caterpillar is without this gene it is incapable of developing, and making the important change to a pupa. And, so fails in its quest to become a butterfly.

Reference, Scientific American, [for the information on the Broad Gene]. All photographs are the copyright of Nick Broomer

The 1st photo depicts a small White larva at 25mm in length, and 2-3mm wide. This is the normal size of a 4th instar larva that is ready to pupate.

A final instar Small White larva at 25mm in length and, ready to pupate

The 2nd photo depicts another 4th instar Small white larva that has grown to the enormous size of 35mm in length [10mm above the normal size for pupation for this species] and, 5mm wide. Far to big to pupate. If this larva had managed to complete its journey and become a butterfly, it probably would of been called a Large Small White. The reason for this abnormality is that this larva was missing that vital gene, the Broad gene and carried on eating until it died without developing any further and not being able to pupate.

A final instar Small White larva at 35mm in length, should only grow to 25mm in length

I n the 3rd photo [just for comparison] it depicts a Small White larva preparing to pupate, now only 19mm in length, the actual size of a fully pupated pupa, [bottom left of the photo]. Whilst in the top right of the photo, you have the overgrown larva at 35mm. Which is genetically incapable of pupating.

Two Small White final instar larva, the one on the left is ready to pupate
the one on the right has failed to pupate and carried on eating
and eventually dies

The 4th photo depicts a final instar White Admiral larva that is probably also missing the Broad gene. Instead of pupating at this stage of it's life, which it should of done, it just stayed on it's leaf without eating until it also died because it was unable to pupate.

Final instar White Admiral larva that failed to pupate