We live at Riversdale on the Wairarapa Coast and many of our trees seem to be defoliated by a nasty brown beetle which lives in the ground.

If they're climbing up the tree try pinning a piece of absorbent cloth soaked in Yates Shield around the trunk. (make sure you use gloves). This will prevent insects running up and will also soak into the tree. Make sure you pin it quite high up the trunk out of the way of pets or kids. You could also try putting some grease on the ridged side of some corrugated cardboard and pin that to tree.