holes in Ludwigia leaves

[Steven Bach <moof1138 at mac_com>]

I have some Ludwigia Repens growing in my tank (29 Gal 2.75 W/Gal Kh 7 
Ph 7, DIY CO2), which has small holes appearing on some leaves, 
sometimes on the edge, sometimes in the center.  When a leaf develops a 
hole it falls off quickly.  Other than the leaf hole thing, it seems to 
be doing well, when I got it it was solid green, it is growing new buds 
and turning red in some spots, and bubbles of oxygen are streaming off 
it in high light areas as well.  The fish in the tank are all Tetras 
(Neon, Glowlight, Gold, and Kerri) and Pencilfish, except for a few 
kuhli loaches and Otos.  I have noticed that the Kerri Tetras 
(Inpaichthys kerri) are eating duckweed off the surface(!), and I have 
seen at least one biting bits of root off of my Cardamine lyrata, though 
he just bites a bit off the tip, spits it out and lets it drops.  I have 
not seen them ever bite a leaf.  I had a few pond snails that snuck in 
and I have been fighting them off, they do not last long when they 
appear, and I have not seen any in a week, but there are new holes. 
Also when I did see them, I never saw them on the Ludwigia, rather they 
were always busy eating algae.  I do have some MTSs living in the 
gravel, but I believe that they are not plant eaters.  There are a lot 
of other plants in the tank, none of which are developing holes.  With 
that data, my questions are:

Has anyone seen a Kerri tetra eat a Ludwigia leaf, or the leaf of any 
plant for that matter?  At the LFS they have a planted tank with Kerri 
Tetras in them, so I figured that they would not be a problem, but now I 
am a little worried.

Is it even possible for them to be the culprits, since some of the holes 
are appearing in the middle of the leaf?  Their mouth shape makes it 
seem unlikely that they could bite the leaf in such a way as to make a 
hole in the middle, though I could be wrong.

Is it possible that the holes are the result of snails that are hiding 
effectively?

Is there any sort of disease that the plant might have that would cause 
leaves to develop holes and fall off?

Is there some reason for the holes to appear that I am missing that you 
might be able to offer?

Thanks for any advice,
Steven