Repellency to Stomoxys calcitrans (Diptera: Muscidae) of Plant Essential Oils Alone or in Combination With Calophyllum inophyllum Nut Oil

The repellency to female Stomoxys calcitrans (L.) (Diptera: Muscidae) of 21 essential oils (EOs) alone or in combination with Calophyllum inophyllum L. (Clusiaceae) nut oil (tamanu oil) was examined using an exposed human hand bioassay. Results were compared with those of commonly used repellent N,N-diethyl-3-methylbenzamide (DEET). In tests with six human male volunteers at a dose of 0.5 mg/cm(2), patchouli (protection time [PT], 3.67 h) was the most effective EO but less active than DEET (4.47 h), as judged by the PT to first bite. Very strong repellency also was produced by clove bud, lovage root, and clove leaf EOs (PT, 3.50–3.25 h), whereas strong repellency was obtained from thyme white EO (2.12 h). Thyme red, oregano, and geranium EOs exhibited moderate repellency (PT, 1.24–1.11 h). At 0.25 mg/cm(2), protection time of clove bud, clove leaf, and lovage root EOs (PT, ≈1 h) was shorter than that of DEET (2.17 h). An increase in the protection time was produced by binary mixtures (PT, 2.68–2.04 h) of five EOs (clove bud, clove leaf, thyme white, patchouli, and savory) and tamanu oil (0.25:2.0 mg/cm(2)) compared with that of either the constituted essential oil or tamanu oil alone (PT, 0.56 h). The protection time of these binary mixtures was comparable with that of DEET. With the exception of savory EO, the other EOs, tamanu oil, and binary mixtures did not induce any adverse effects on the human volunteers at 0.5 mg/cm(2). Thus, binary mixtures of essential oils and tamanu oil described merit further study as potential repellents for protection from humans and domestic animals from biting and nuisance caused by S. calcitrans.