Hi folks,

Resident zoologist here :-)
The 'powder' is actually thousands of tiny coloured overlapping scales
covering the wing surfaces. They are modified hair cells. They may also
contribute to the wing aerodynamics, hence, the animal can no longer fly
if the scales are lost. They certainly give the colour and shimmer to
the wing membranes, which are otherwise colourless.

Here endeth the lesson ;-)

Deb.

When I was a teenager, I once found a huge caterpillar walking across
a parking lot.  It was about five inches long and one inch thick,
blue-green with orange horns on each segment.  I went home, got an
empty jar, punched air holes in the lid, went back to the parking lot,
and captured the caterpillar.

By the time I got home, the caterpillar had started weaving a cocoon
inside the jar.  The jar, and cocoon, sat on our kitchen table all
winter.  In the spring, the former caterpillar, now a Cecropia moth,
started hatching out.  I released it onto a tree branch outside the
kitchen window, and, within an hour, another such moth had arrived to
mate with it.  They then both flew away, and I never knew where it lay
its eggs.

Here is another web page describing the moths, and showing both the
adult and juvenile forms:
http://www.ivyhall.district96.k12.il.us/4th/kkhp/1insects/cecropia.html