Bug theory

Something has been wrong with this house foliage plant called Ficus Umbellata.
Here and there on the surface of leaves is sticky liquid. I took a lick of it. Sweet!
When Mrs. toshi4374 looked carefully deep into the foliage, she at last found the cause. She turned her look to me and proudly said, "Bugs".
These brown dots of creatures in the picture are what we call "sea-shell bugs" or in English "scale insect". うろこ虫か、なるほど。
My Internet search revealed parasitic nature of the insect that sucks up sap from trees and excrete sweet sticky liquid. But there's no description anywhere at all about how they, basically stationary insect as they are, (which do not move around) walked or crawled all the way to the center of a large leaf and left the sweet liquid. So I'm still skeptical about the bug as a culprit.
It is said a good many of tropical plants have honey glands from which they secrete honey. This theory sounds more convincing to me.
Somehow Mrs toshi4374 likes the bug theory. She argues that if a house foliage plant naturally excreted such sticky liquid, no body would like to buy it. And here are bugs. When the two facts are put together, the conclusion is the bug did it. Doesn't matter how they did, but ANYWAY they did it.
She picked up the bugs, crushed them between her fingers and said "Let's see whether the sweet stuff will be ever on the leaf again."
Fair enough.