Re: Fw: Plant pest.
You may be compounding your critters. Insect contols have been
introduced for Eichhornia and I also believe for Pistia, but it was
after extensive testing and they have been shown to be species selective
in their dietary preferences.
The insect you describe sounds to me to be a widespread aquatic plant
pest known commonly as the China Mark Moth or more colloquially as the
"Sandwich Man". They range from at least here in S Fl to Central TX and
will damage about any aquatic plant, but are not the insects released to
control Eichhornia or Pistia. I don't have it in front of me, but can
get you the latin name for the Mark Moth if you wish.