"Adults take a variety of foods, many feeding on fungus, dung, carrion, or other decomposing matter, some on sap, pollen/nectar, fruit, foliage; a few are agricultural pests, others, important pollinators. Larvae typically feed on decomposing matter: dung, carrion, etc., or live in soil and feed on roots "
This is from the Bugguide page on Scarab beetles:
http://bugguide.net/node/view/...
It depends on the species whether the larvae feed on plant roots or not.
I agree about the extension office if you are concerned. This might help:
http://ucanr.edu/County_Office...
