If you grow
Rhododendrons or yews, you may have
encountered the damage caused by the adult of the black
vine weevil. Due to the shape of their mouthparts, these
night feeding pests leave what is described as a
"half-moon" notch at the edge of the leaves. It is very
distinctive and it may do the same type of feeding
damage to hostas.
For woody plants, the
more significant damage is done by the larvae of these
insects feeding on the roots. That is why the major
control measures for this insect are to treat the soil
around the plants.
If these are bothering
your hostas, check other nearby shrubs and see if they
are being damaged too. If so, you may need to treat them
to control the problem. A non-chemical alternative would
be to go out at night with a flash light to see if you
can catch the adult. Be sure to alert your neighbors
about what you are doing poking around in the dark.