a pest bored into my phalaenopsis

[vabene]

about a year ago a friend gave me an orchid which had been transplanted into dirt. I repotted it into some moss and a little bark and it immediately began to thrive with new roots, leaves and then a stem with buds. The first flower opened about 2 months ago and was beautiful, but about 2weeks ago, I notices that it had wilted. Since then the leaves have been turning yellow. Tonight when i pulled one off, I noticed that the underside of the leaf had a white residue that looks like a cocoon from a moth or some larva. When i checked the plant more carefully, it seems that something has bored into the base of the plant. Any suggestions about what this could be?