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.

Larvicide Activity on Aedes aegypti of Essential Oil Nanoemulsion from the Protium heptaphyllum Resin

“…Study of the larvicidal activity of Carlina acaulis essential oil and the nanoemulsion prepared from it, against the larvae of Lobesia botrana , showed LC 50 = 7.29 (6.90–7.60) and 9.04 (8.60–9.70), respectively, and LC 90 = 10.92 (9.70–13.60) and 17.70 (15.40–27.50), respectively [ 29 ], showing a lower efficiency for nanoemulsion when compared to essential oil in natura . The study of larvicidal activity, against Culex quinquefasciatus larvae, with the essential oil obtained from the leaves of Smyrnium olusatrum , isolated isofuranediene and microemulsion 750 of isofuranediene, showed LC 50 of 18.60 (15.70–21.30); 29.20 (24.80–34.10) and 17.70 (16.40–19.20), respectively, and LC 90 of 32.30 (29.90–35.80); 86.70 (70.80–103.10) and, 39.10 (33.10–49.70), respectively [ 30 ], demonstrating better responses of LC 50 for the microemulsion and LC 90 for isolated isofuranediene.…”

Back to the Roots—An Overview of the Chemical Composition and Bioactivity of Selected Root-Essential Oils

“…Various recent studies have highlighted the promising impact of C. acaulis root EO as a source for botanical insecticidal products [ 10 , 81 , 95 , 97 , 99 , 100 ]. Insecticidal screening of eight different EOs against Prostephanus truncatus and Trogoderma granarium adults—two stored-product beetles—revealed C. acaulis as an effective alternative grain protectant [ 10 ].…”

“…However, if applied at the same concentration, the EO encapsulated in the NE was found to be more effective than pure C. acaulis EO. This might be related to a better interaction between the active substance and the target site, alongside a guaranteed conservation of the EO’s insecticidal activity through encapsulation, ensured dispersibility in the environment, and long-time stability [ 100 ]. Moreover, C. acaulis EO exerted an outstanding toxicity against (3–5 days old) housefly Musca domestica L. adults (LD 50 = 2.74 and 5.96 µg/fly for males and females, respectively).…”

Developing a Hazomalania voyronii Essential Oil Nanoemulsion for the Eco-Friendly Management of Tribolium confusum, Tribolium castaneum and Tenebrio molitor Larvae and Adults on Stored Wheat

“…Mortality levels reached 80% after 24 h and 90% after 48 h at 250 ppm. Recently, Benelli et al [27] proposed a 6% (w/w) NE of Carlina acaulis L. (Compositae) root EO against the European grapevine moth, Lobesia botrana (Denis and Schiffermüller) (Lepidoptera: Tortricidae), reaching 50% and 90% mortality of 1st instar larvae with 9.04 and 17.70 µL/mL, respectively. In a further recent study, Pavela et al [32] evaluated NEs based on C. acaulis EO and found that less than 1200 µL/L caused 90% mortality to 3rd instar larvae of Culex quinquefasciatus Say (Diptera: Culicidae).…”

“…Thanks to the reduced size of the droplets of the internal phase and the consequent increment of the surface area, NEs allow a better interaction of the encapsulated compounds into the target site [ 23 ] by overcoming the EO’s poor physicochemical stability and solubility issues [ 24 ]. This strategy can boost the applicability of EOs as natural insecticides [ 25 , 26 , 27 , 28 , 29 ].…”