cherry slug?

there are worms on my cherry and plum trees, which are eating windowpane type holes in the leaves. a google image search brought me to this:
http://www.gardensafari.net/pics/wespen/zaagwespen/caliroa_cerasi_hs0_2370.jpg
they call it a "cherry slug", and say it's a sawfly larva, but i can only find info on it in non-US websites. i live in WA state in the US, so i'm wondering if this is a native pest, or something that got imported with my trees (i have no idea where they came from).
will this pest go away with the winter, or do i need to spray my trees now? is there an effective biological control? or am i reduced to use a soap spray?
thanks,
-kelly
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http://www.gardensafari.net/pics/wespen/zaagwespen/caliroa_cerasi_hs0_2370.jpg
now?
These are the larvae of the pear sawfly and are not exotic pests - pretty common to many areas of the country and are very fond of pears, cherries, plums, hawthorns, etc. They have a number of natural predators and can be controlled both by spraying off with a strong stream of water or by using insecticidal soap. Not much point in doing anything right now, as the trees will be dropping their leaves (and the slugs) soon. Monitor them in the spring after the new leaves emerge and treat then as necessary.
pam - gardengal
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fantastic, this is just what i was hoping to hear.
thanks!
-kelly
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