Exploring the Insecticidal Potential of Boldo (Peumus boldus) Essential Oil: Toxicity to Pests and Vectors and Non-target Impact on the Microcrustacean Daphnia magna.

Roman Pavela,Giovanni Benelli,Loredana Cappellacci,Filippo Maggi,Stefano Dall’Acqua,Giulio Lupidi,Riccardo Petrelli,Stefania Sut

doi:10.3390/molecules24050879

Abstract

Every year Chile exports about 2000 tons of boldo folium (Peumus boldus), which is used around the world as a traditional herbal medicinal product (THMP), mostly to relieve gastrointestinal disorders. This biomass may be a resource for the agrochemical industry to manufacture botanical insecticides. In this regard, the insecticidal potential of boldo has been poorly investigated. In the present work, hydrodistillation of a commercial boldo folium gave 1.5% (w/w) of a yellowish essential oil (boldo essential oil, BEO) containing 1,8-cineole (20.7%), p-cymene (18.5%), limonene (9.1%), ascaridole (9.1%) and β-phellandrene (6.4%) as the main constituents, as determined by gas chromatography-mass spectrometry (GC-MS). NMR analysis allowed us to determine that ascaridole was mainly represented by the cis-isomer. BEO was toxic to larvae of the filariasis vector Culex quinquefasciatus and adults of the housefly Musca domestica, showing LC50/LD50 values of 67.9 mg·L−1 and 98.5 µg·adult−1, respectively. On the other hand, lower insecticidal activity was observed against larvae of the moth pest Spodoptera littoralis (LD50 of 268.9 µg·larva−1). It is worth noting that, when tested at LC90 concentration, BEO was significantly less toxic to aquatic microcrustacean Daphnia magna than the conventional insecticide α-cypermethrin. Finally, in the attempt to explore the BEO mode of action, we tested it for acetylcholinesterase (AChE) inhibitory properties using the Ellman method, obtaining negligible effects (IC50 = 0.45 mg·mL−1). Taken together, these results gave new insights into the potential of BEO as a future ingredient of botanical insecticides.

Highlights

Boldo (Peumus boldus Molina) is an evergreen tree belonging to the Monimiaceae family and native to temperate regions of Chile
We evaluated the toxicity of boldo essential oil (BEO) on larvae of the filariasis, Culex quinquefasciatus Say, adults of the housefly, Musca domestica L
Our findings indicate that the analyzed BEO can be considered a relatively safe pest and vector control product, due to the low content of ascaridole, presenting a potential use in the area of botanical insecticide development

Summary

Introduction

Boldo (Peumus boldus Molina) is an evergreen tree belonging to the Monimiaceae family and native to temperate regions of Chile. Molecules 2019, 24, 879 habitus, occurring as a single plant or in forests between the flat areas and the coastal cordilleras [1] The part of this species that is used is the leaf (boldo folium), which is simple, ovate, greyish-green on the upper side and whitish on the lower, shortly petioled, hard and with a pleasant smell. The spongy mesophyll is full of oil glands producing a brownish-yellow oil (yield of 1–2%) of camphoraceous odor, aromatic taste, containing 1,8-cineole, p-cymene and ascaridole as the major components [3] The latter is matter of concern due to its toxicity so that ascaridole-containing boldo preparations should be managed carefully for human use [4]

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Conclusion