Nanoemulsified Formulation of Cedrela odorata Essential Oil and Its Larvicidal Effect against Spodoptera frugiperda (J.E. Smith)

Abstract

Cedrela odorata L. is a plant species from the Meliaceae family that is cultivated for timber production. Although the C. odorata essential oil (EO) contains mainly sesquiterpenes, its insecticidal potential is unknown. The lipophilic properties and high degradation capacity of EOs have limited their application for use in pest control. However, the currently available knowledge on the nanoemulsification of EOs, in addition to the possibility of improving their dispersion, would allow them to prolong their permanence in the field. The objective of the present work was to develop a nanoemulsion of the C. odorata EO and to evaluate its larvicidal activity against Spodoptera frugiperda. The EO was obtained by the hydrodistillation of C. odorata dehydrated leaves, and the nanoemulsion was prepared with non-ionic surfactants (Tween 80 and Span 80) using a combined method of agitation and dispersion with ultrasound. The stability of the nanoemulsion with a droplet diameter of <200 nm was verified in samples stored at 5 °C and 25 °C for 90 days. Both the C. odorata EO and its corresponding nanoemulsion presented lethal properties against S. frugiperda. The results obtained provide guidelines for the use of wood waste to produce sustainable and effective insecticides in the fight against S. frugiperda. In addition, considering that a phytochemical complex mixture allows the simultaneous activation of different action mechanisms, the development of resistance in insects is slower.

Keywords: botanicals; fall armyworm; sustainable insecticides; wood waste.

Figure 1

Mass spectrum of the major compounds identified in the Cedrela odorata essential oil. identification with the mass spectrum of the NIST library. (A) Germacrene D, identification with an approximation of 97.3%. (B) Caryophyllene, identification with an approximation of 96.7%.

Figure 2

Texture of the Cedrela odorata essential oil (10%) and water (75%) mixture after their emulsification with different mixtures (15%) of the surfactants Tween 80 and Span 20. Hydrophilic–Lipophilic Balance (HLB) value of the surfactant mixtures: (A) 8.98; (B) 10.01; (C) 10.46; (D) 10.78; (E) 11.03; (F) 11.48; (G) 12.06; and (H) 12.89.

Figure 3

Emulsions of the Cedrela odorata essential oil with different binary mixtures of surfactants of HLB = 10.46 and a 10:15:75 (essential oil:surfactant:water) ratio: (A) emulsions prepared with magnetic stirring and heating; and (B) dispersion of oil droplets using ultrasound in cycles of 2 min.

Figure 4

Emulsions of the Cedrela odorata essential oil in terms of the essential oil:surfactant mixture:water ratio: (A) 2.5:5:92.5; (B) 5:5:90; (C) 5:10:85; and (D) 5:15:80. Surfactant mixture (Tween 80–Span 80) of HLB = 10.46.

Figure 5

Dynamic light scattering (DLS) diagrams of the droplet diameter in the nanoemulsions: (A) 2.5:5:92.5; and (B) 5:10:85.

Figure 6

Transmission electron microscopy (TEM) morphology of the micelles in the nanoemulsion of the Cedrela odorata essential oil. The red arrows show the predominant droplet diameter in the DLS analysis at day 30 in samples stored at 5 ± 2 °C.

Figure 7

Mortality (mean (%) ± SE) of first-instar larvae of Spodoptera frugiperda measured by the effect of the concentration (mg kg⁻¹) of the Cedrela odorata essential oil, alone or in a nanoemulsified formulation. Mortality was recorded on day seven. Positive control: neem essential oil; negative control: Tween 80–Span 80 surfactant mixture. Two-way ANOVA. Dots with the same letter (a–h) do not significantly differ (Bonferroni test for an α = 0.05).

Figure 8

Chromatograms of the Cedrela odorata essential oil: (A) oil extracted with dichloromethane from the nanoemulsion of the C. odorata essential oil at 2.5%; and (B) oil extracted by hydrodistillation from the C. odorata dehydrated leaves. Major components: 1 = germacrene D; 2 = caryophyllene; 3 = cis-α-bisabolene; and 4 = copaene, 5 = phytol.