Developing a Highly Stable Carlina acaulis Essential Oil Nanoemulsion for Managing Lobesia botrana

Abstract

The growing interest in the development of green pest management strategies is leading to the exploitation of essential oils (EOs) as promising botanical pesticides. In this respect, nanotechnology could efficiently support the use of EOs through their encapsulation into stable nanoformulations, such as nanoemulsions (NEs), to improve their stability and efficacy. This technology assures the improvement of the chemical stability, hydrophilicity, and environmental persistence of EOs, giving an added value for the fabrication of natural insecticides effective against a wide spectrum of insect vectors and pests of public and agronomical importance. Carlina acaulis (Asteraceae) root EO has been recently proposed as a promising ingredient of a new generation of botanical insecticides. In the present study, a highly stable C. acaulis-based NE was developed. Interestingly, such a nanosystem was able to encapsulate 6% (w/w) of C. acaulis EO, showing a mean diameter of around 140 nm and a SOR (surfactant-to-oil ratio) of 0.6. Its stability was evaluated in a storage period of six months and corroborated by an accelerated stability study. Therefore, the C. acaulis EO and C. acaulis-based NE were evaluated for their toxicity against 1st instar larvae of the European grapevine moth (EGVM), Lobesia botrana (Denis & Schiffermüller, 1775) (Lepidoptera: Tortricidae), a major vineyard pest. The chemical composition of C. acaulis EO was investigated by gas chromatography-mass spectrometry (GC-MS) revealing carlina oxide, a polyacetylene, as the main constituent. In toxicity assays, both the C. acaulis EO and the C. acaulis-based NE were highly toxic to L. botrana larvae, with LC₅₀ values of 7.299 and 9.044 µL/mL for C. acaulis EO and NE, respectively. The C. acaulis-based NE represents a promising option to develop highly stable botanical insecticides for pest management. To date, this study represents the first evidence about the insecticidal toxicity of EOs and EO-based NEs against this major grapevine pest.

Keywords: European grapevine moth; Integrated Pest Management; Larvicide; Tortricidae; green pesticide; insect pest; nano-insecticide.

Figure 1

Gas chromatography–mass spectrometry (GC–MS) chromatogram of the essential oil obtained from the roots of Carlina acaulis. The separation of peaks was achieved using a HP-5MS (5% phenylmethylpolysiloxane, 30 m length × 0.25 mm internal diameter, 0.1 μm film thickness).

Figure 2

Dynamic light scattering (DLS) traces of Carlina acaulis essential oil-based nanoemulsion, at different time points: 0 day (t0), 1 month (t1), 3 months (t3), 6 months (t6).

Figure 3

Carlina acaulis essential oil nanoemulsion (EO NE) at t0 (A), after the centrifugation (B), after the heating–cooling cycles (C) and after the freeze-thaw cycles (D).