Yponomeuta

In Bessans (High-Maurienne Valley), this group of wild cherry trees offered a very sad aspect in the very hearth of July, since it had lost almost all its leafs...

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The culprit for this desolation is a tiny white butterfly, called Ermine (Yponomeuta sp.), whose caterpillars can devore all leafs very rapidly.

The genus Yponomeuta counts about thousand described species in the world (see the Wikipedia page), but only about ten in Europe. Since the species Yponomeuta evonymella (see the Wikipedia page) feeds specifically on wild cherry trees (Prunus padus), we can rather safely say it is this species, albeit it is very difficult to ascertain the precise species without examining the genitalia. In particular, the black dots can't be a criterion.

The caterpillars of this butterfly live in a collective cocoon they weave in the tree where they hatched in the springtime.

They feed on leaves and devore everything in their reach.

Then comes the time of pupation. The caterpillars form individual cocoons in the collective one where they lived.

When the imagos appear, the wings are not yet functional. They must wait a little time, which leaves us the occasion to see the back wings, with their lead grey colour.

Adult butterflies can also be seen on other plants...

Sometimes very busy to propagate their genotype...

However, the vitality of the trees is so strong that they produce rapidly new leaves, as soon as the strength of the attack declines.

In summer 2013, that is six years later, I had the occasion to come again at the same spot, justa little later (end of August instead of mid-July). I could understand that my optimistic considerations above were rather false.
The picture shows the very same tree, from the same angle. It remains less than the half of the original tree. It seems that the tree always tries to produce new leafs but can't manage to come to the fructification phase.

There was as always collective cocoons, but they were not on some branches, but on the whole tree. The last picture of this page is rather depressive.

A couple of years later, the deed is done. The cherry tree is dead. A young Alnus incana is trying to grow at its place. Would you believe that butterflies could kill a tree?

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