Eating Elm

Top Photo: Larger elm leaf beetle larva feeding on elm leaves.

Back at the end of May, we Rangers discovered many adult, larger elm leaf beetles on the far side of the museum’s outdoor loop between Explore the Wild and Catch the Wind. The beetles were all down low on the vegetation and boulders that line the path in that area. The insects weren’t eating but slowly walking about on the rocks and mostly poison ivy leaves, presumably to find mates.

Adult larger elm leaf beetle.

After a few weeks the beetles disappeared and were, more or less, forgotten.

Large numbers of adults gathered in late May and early June.

It’s now August and I’d been away from the museum for nearly two weeks. I’ve been told, in my absence, something had been, and still is, eating the leaves on the various elm trees in Catch the Wind. Hmmm.

A walk over to one of the trees being devoured, or rather its leaves being skeletonized, revealed small (1/2” – 3/4”) orange-brown grub-like creatures at work on the leaves. Could these skeletonizing larvae be the results of the beetle congregation in late May and early June?

Leaving little more than the main veins of the leaves.

A quick search found that yes, these were larger elm leaf beetle larvae fast at work transforming the elm leaves from photosynthesizing factories to mere skeletons.

Larger elm leaf beetles (Monocesta coryli) are widespread in the east. The adults are yellow to orange with large black or brown spots or blotches both posteriorly and anteriorly on the elytra.

The larvae bring to mind little concertinas. No mere squeezeboxes though, these little eating machines devour elm leaves leaving nothing but the larger veins of the leaves, a skeleton. Besides elm, the larvae may also feed on dogwood, hazelnut, pecan, river birch, plum, and hawthorn.

Little larva at work.

Though they can do considerable damage to tree’s leaves, research suggest they persist for a year or two then, apparently, disappear from the area. Previous to this year, the last time I photographed one of these beetles here at the museum was in 2010 and hadn’t noticed any tree damage till this year.

There’s another elm leaf beetle in our area, the elm leaf beetle (Xanthogaleruca luteola) about half the size as the larger elm leaf beetle. It, the elm leaf beetle, was introduced into the United Staes from Europe around 1838 and is found throughout the country.

The larger elm leaf beetle is native to North America.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.