This is the larva of the Tortoise Beetle
Silana farinosa. It was described as an introduced pest from Sril Lanka and the Indian subcontinent. It is a pest that feeds on and practically defoliates large bushes/trees of the Indian Curry Leaf (
Murraya koenigii).
This is the first time that I've seen it feeding on a
Citrus (Lime) plant. Both
Murraya and
Citrus belong to the plant family
Rutaceae, so it may not be unusual for the pest to migrate to another plant in the same family.
There are articles on the Internet describing the biology of this pest, and I have one that was written in the Malayan Nature Journal some time ago. The larva has a strange habit of carrying its excreta in a bag
and that's that big bulgy thing that you see in your photo.
The only shot that I came across on the Internet is
this one , which shows the adult beetle (fresh specimens usually appear as a white oval things and fly for short distances when disturbed), and a very unclear shot of the larva on the bottom right hand corner of the picture.