Nanoemulsões de Lavandula dentata e de Myristica fragrans: desenvolvimento, estudo de estabilidade e efeito inseticida

Abstract

Essential oils have been widely studied in relation to insecticidal activity as an alternative to conventional insecticides, since the widespread of synthetic compounds has caused damage to health and environment, as well influenced the growing number of resistant species. In this sense, the essential oils of Myristica fragrans (nutmeg) and Lavandula dentata may be an alternative for the control of the Muscidae and Calliphoridae families. The objective of this work was to investigate the insecticidal activity of nanoemulsion and free oils in relation to the species Musca domestica and Chrysomya albiceps. Extraction of essential oils from M. fragrans seeds and aerial parts of L. dentata were conducted by hydrodistillation and the oils obtained were evaluated for their chemical composition. The main components identified were beta-pinene (26%), alpha-pinene (10.5%) and sabinene (9.1%) monoterpenoids in M. fragrans; and 1,8-cineole, camphor and linalool oxide for L. dentata. The nanoemulsions containing the oils were prepared by emulsification method under high agitation and evaluated for mean droplet diameter (64-87 nm), polydispersity index (less than 0.26), negative zeta potential (11- 14 mV) , pH (weak acid), content of the compounds (close to free essential oil values) which were adequate and better stable under cooling (4 ° C) temperature conditions. To determine the insecticidal activity were evaluated the effects of free oils and nanoemulsions regarding larvicide and adulticide action. Essential oils under study in the free form at 5% (b/w) were effective against larvae of M. domestica. Regarding the adulticidal effect, the essential oil of L. dentata presented toxicity in both species; the lethal concentration (LC50) by the superficial application method was, respectively, 3.13 ± 0.64 and 1.39 ± 0.19% (b/w) for M. domestica and C. albiceps; LC50 by the exposure test was 4.15 ± 0.64 and 5.14 ± 0.81% for M. domestica and C. albiceps, respectively. The topical application of M. fragrans essential oil was more toxic to C. albiceps, with LC50 values of 2.02 ± 0.56, than for common fly (LC50 = 8.57 ± 2.41%). As for the impregnated paper exposure test, the oil were very effective for M. domestica (LC50 = 2.74 ± 0.24%) and C. albiceps (LC50 = 3.65 ± 0.48%). Both nanoemulsions produced an insecticidal effect by topical application and fumigant effect, being the nanoemulsions of M. fragrans essential oil effective by fumigant effect for both insect species and lavender essential oil nanoemulsions at 5% effective in C. albiceps by the same method. Topical toxicity was also observed for nanostructured systems, with NE-OM 5% causing mortality in C. albiceps whereas NE-OL 5% was more toxic to M. domestica. It was possible to verify that the inhibitory effect observed in the enzyme acetylcholinesterase has been shown to have a relation with the insecticidal activity. Thus, the formulations developed in this project may contribute to the development of an insecticide containing a natural product for the control of flies.