Hello. So, according to a talk I recently heard by a vector borne disease scientist at the California Department of Public Health:

1. Full strength DEET is unnecessary. Regular DEET is fine.

2. Oil of lemon of eucalyptus is also an effective repellent.

If folks bring DEET, the rangers do not recommend that you put it in your BearVault. It destroys plastics, polycarbonate, etc.

Here are some links.

http://www.nps.gov/yose/planyourvisit/health.htm

http://westnile.ca.gov/wnv_faqs_basics.php (focused on West Nile)

http://www.cdc.gov/westnile/faq/repellent.html (same)