I was out and about at various Long Island field sites this past Monday, collecting Glossy Buckthorn leaves for a colleague in Belgium, and I noticed something I've never seen before - rampant herbivory of Glossy Buckthorn. Here's an example of what it looks like.
I sent an email to a friend at UNH who has studied buckthorn many years now, and asked him if he's seen anything like this. No, he hasn't, but he's heard of this type of herbivory on buckthorn from a colleague in the Kittery, Maine area. So based on this lead, the suspect is the larva of the moth Magusa divaricata. Sadly, these days I'm pretty busy finishing my PhD, doing my postdoc work, finishing up various projects, etc, so I don't think I'm going to be able to squeeze in more field time in the immediate future to seek out what's eating the buckthorn, but maybe I'll get lucky when I go out to collect data later this October (though I suspect the moths will be long gone by then). In any case, it's an interesting observation to stow away and come back to in the future.