Surfactant‐enhanced essential oils as mosquito larvicides

Abstract

Abstract Using laboratory bioassays with fourth‐instar Culex pipiens form molestus larvae, we explored the larvicidal properties of two representative plant‐derived oils, eucalyptus oil and turpentine (two grades), and cineole, the main component of eucalyptus oil. Each was larvicidal alone, but efficacy was enhanced when the spreading pressure was increased by adding 1% insoluble surfactant (Arosurf MSF) plus 1% detergent. Cheap turpentine was more effective than more refined turpentine. These mixtures were compared with the familiar surface‐active larvicides Arosurf and Golden Bear Oil. At a dose of 2 μl per tub (=0.13 μl cm −2 ), enhanced by surfactants (turpentine:Arosurf:detergent 100:1:1 by volume), refined turpentine acted faster than Arosurf alone, causing higher mortality at 24 and 48 h after treatment but equivalent mortality at 72 h. It immobilised more larvae than Golden Bear Oil in the first three hours, but was less effective over 24 h. Crude turpentine enhanced by surfactants immobilised about as many larvae as Golden Bear Oil over 24 h. These findings indicate that plant essential oils merit further attention as widely available, environmentally benign mosquito larvicides.