Characterisation of Actions of p-menthane-3,8 diol (PMD) Repellent Formulations against Aedes aegypti mosquitoes

Background Characterisation of mosquito repellents using arm-in-cage tests are performed by assessing the ED95, half-life and complete protection times (CPT). This study fully characterises p-menthane-3,8 diol PMD which has not been widely studied, and a long-acting formulation containing a PMD-vanillin composite. Method A series of arm in cage tests against Aedes aegypti aegypti (Dipera-Culicidae) strain mosquitoes were devised using 6 volunteers to estimate CPT or 10 to estimate the effective dose (ED95) and half-life for three repellents: 20% DEET, 30% PMD and a novel 30% PMD-vanillin formulation. Non-linear Regression analysis was used to characterise the relationship between applied dose and CPT. were also estimated Results PMD and DEET showed a very similar log dose relationship to CPT; however, the PMD-vanillin formulation exhibited a sigmoidal ‘S-shape’ relationship. This resulted in a 1.5 times higher CPT for PMD-vanillin compared to that of 20% DEET when applied at a dose of 1.6mg/cm2, but little difference at lower doses of 0.8-1mg/cm2. The ED95 value for the 30% PMD and PMD-vanillin formulations were 0.25 and 0.24 mg/cm2 respectively, these being higher than that for 20% DEET (0.09 mg/cm2). The half-lives for 30% PMD and 20% DEET were similar (2.23 vs. 2.74 hrs.), but longer for the PMD-vanillin formulations (3.8 hrs.). Conclusion Such a full characterisation for other repellent formulations, particularly those claiming extended longevity, should be conducted in order to identify differences at various applied doses.