There are several ways

1. Beetle traps. You can buy these at any hardware stores or Home
Depot. One big word of advice. Place them AWAY from your trees like
on the other side of the house. You want the beetles to flly AWAY
from your trees. I have hybrid T roses and these beetles LOVE to eat
the roses and the beetle traps diminish the beetles by about 95 %.

2. Buy some worms called nematodes from a garden store or mail order
and put them in the soil. They eat the beetle larvae. They won't work
right away, but over time they will.

3. I read this from a magazine and have yet to try this. It seems
that beetles are attracted to bright colors, specifically white. Hang
a white sheet , again away from your trees but on your property.
Supposedly the beetles will congregate on the white sheet and you can
pick them off with soapy water and then dump them in the water. I
haven't tried this yet.

Nitsupak
Nitsupak Art & Photograhy (http://www.cafepress.com/nitsupak)