Interesting topic.
You'll often see tell tale signs of lerps on euclyptus leaves, usually after they have been. But severe infestations could kill a tree and more so if these miner birds are around.
Here's a fine links to some information.
http://www.nationalparks.nsw.gov.au/...eback_strategy http://www.dpi.vic.gov.au/dpi/nrenin...256DEA0027CFDF http://bugs.bio.usyd.edu.au/Entomolo...ges/lerps.html