Beware the Bronze Birch Borer

We're under attack! From the Bronze Birch Borer beetle. We trimmed off dead branches and removed the fourth trunk from this clump yesterday but couldn't reach the dead stuff at the top of one of the trees. Here's what it looks like when these guys get to your beloved paper birch and start killing it at the crown:

It's a Big Bummer. This has been a great tree for us. We injected some insecticide into the base of the surviving trunks. Maybe that will help, but the outlook seems grim.

(Our friends up in Canada have an informative page about insect pests that links to a brochure about the Bronze Borer. Nasty little biter.)