Carlina acaulis L. (Asteraceae): biology, phytochemistry, and application as a promising source of effective green insecticides and acaricides

Carlina acaulis L., belonging to the Asteraceae (Compositae) family, is a perennial herb native to the Alps, which has a long history as a food and traditional remedy , being one of the most important medicinal plants in Europe. Its reported uses go from diuretic, cholagogic, and antibacterial agent for the treatment of gastritis, skin diseases, acne, eczema, and ulcers. Even if this plant presents a rich phytocomplex, its root essential oil (EO) is the product that surely raised most research interest. It has the exceptional feature of having as main constituent the polyacetylene carlina oxide, and is currently listed among botanicals employable in food supplements in Europe. This EO and carlina oxide showed an encouraging bioactivity on a variety of bacteria and fungi, such as Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris, Candida albicans and C. glabrata. Moreover, these products showed marked insecticidal and acaricidal activities against insect pests and vectors of medical, agricultural, and economic importance, revealing to be promising in the horizon of botanical insecticides and acaricides. Its EO as well as carlina oxide resulted to be active on vectors, e.g. Culex quinquefasciatus, urban and livestock pests e.g. Musca domestica, stored product pests e.g. Acarus siro, Trogoderma granarium and Prostephanus truncatus, and agricultural pests, e.g. Lobesia botrana, Bactrocera oleae and Ceratitis capitata, among others. These insecticidal properties are also accompanied by low-to-moderate toxicity on non-target organisms such as earthworms and aquatic microcrustaceans, as well as on vertebrate cells and mammals. Innovative formulations have been developed and tested for applying these products in real-world conditions with encouraging results. Different cultivation systems of C. acaulis have been carried out, with classic field cultivation having the greatest advantage over other systems, such as hydroponic and in vitro micropropagation in terms of insecticidal and acarcicidal compound yield. This review puts a focus for the first time on C. acaulis, its active compounds and its potential against vectors, pests, and pathogens, and on current issues related to its cultivation on a large-scale level. Moreover, its biological properties and related encapsulation techniques developed are extensively reviewed.