Here at DoceLunas in Jaco, Costa Rica, we are on sloping well drained ground, but we still get a few mosquitoes. We are working on our own natural mosquito repellent mix using several botanicals. It is hard with a small sample size to be sure it works, but it seems to be somewhat effective to wear citronella or lemon eucalyptus.
While there is not a reliable study showing that the pure botanicals are effective, a recent US Center for Disease Control publication suggests that lemon eucalyptus may be, because CDC says synthetic lemon eucalyptus is effective.
Oil of lemon eucalyptus (OLE) or PMD (chemical name: para-menthane-3,8-diol), the synthesized version of OLE. Products containing OLE and PMD include, but are not limited to, Repel and Off! Botanicals. This recommendation refers to EPA-registered repellent products containing the active ingredient OLE (or PMD). “Pure” oil of lemon eucalyptus (essential oil not formulated as a repellent) is not recommended; it has not undergone similar, validated testing for safety and efficacy, is not registered with EPA as an insect repellent, and is not covered by this recommendation.
So there you have it, use Repel and Off Botanicals and you don’t have to use DEET anymore!
Here is a link to the CDC report: