Incorporation of essential oil from Vitex gardneriana (Lamiaceae) in microemulsions systems based on mineral and cottonseed oils increased its bioactivity against a coconut pest mite

Coconut (Cocos nucifera L.) is an important cash crop for Asia, Africa and tropical America. The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae) is a major coconut pest, inflicting heavy damage to fruits, thereby reducing yields and farmers profitability. Previous research has demonstrated that high contents of sesquiterpenes compounds present in the essential oil of Vitex gardneriana Schauer (Lamiaceae) (EOVG) showed high potential to control A. guerreronis. Systems stabilized by surfactants, such as microemulsions (MEs), are promising to carry essential oils due to their solubilization and protection properties, generally allow for greater spreadability, wettability and have thermodynamic stability and lower viscosity. Here, we compared the acaricidal activity of MEs containing EOVG a based cottonseed oil (CO) and mineral oil (MO) as different oily phases. MEs formulations were obtained through the pseudoternary phase diagram using a 1:1 mixture of polysorbate 80: propylene glycol as surfactant and co-surfactant, respectively, and CO and MO as oily phases and water as aqueous phase. The MEs were characterized by polarized light microscopy, dynamic light scattering as well as by rheological behavior. Results based on concentration-mortality bioassays, showed that the toxicity of ME-CO containing EOVG was higher (LC50 = 195 ppm) in comparison with ME-CO without EOVG (LC50 = 669 ppm). Similarly, adding EOVG to ME-MO increased the toxicity further (LC50 = 120 ppm). Moreover, the LC50 of ME with and without EOVG for A. guerreronis was higher than the LC50 determined for the EOVG alone (LC50 = 888 ppm). The MEs containing EOVG in their LC80 and mainly LC50, repelled the mite. Overall, our results indicate that the MEs hold potential for controlling A. guerreronis, especially when EOVG was added with both oil phases.