Carlina acaulis: a promising candidate for eco-friendly botanical pesticides

During the era of increasing urbanization, global warming, and enhanced food production, managing different populations of vectors and insect pests is becoming an issue of global interest. Furthermore, the uncontrolled use of chemical pesticides led to the alarming development of resistance in targeted species, but also non-targeted effects on human health and the environment. Therefore, new eco-friendly and reliable pesticides to control insect pests and vectors are needed. For this purpose, plant-derived products are nowadays widely investigated, with particular attention to essential oils and their chemical constituents, given their efficacy on different insect species. Carlina acaulis (Asteraceae) is an alpine perennial herb, with a long and considerable history as traditional remedy and food, which makes it one of the most used medicinal plants in Alpine regions of southern and central Europe. C. acaulis root and its essential oil are reported in the Italian list of botanicals to be used in food supplements and in the Belfrit list, where they are indicated as diaphoretic, eupeptic, carminative and diuretic. The root essential oil, which is mainly composed of carlina oxide, has shown several biological properties, such as antitrypanosomal and antimicrobial activities. However, limited attention has been given to its insecticidal potential. The work of our group focused on the insecticidal activities of the essential oil and of its major constituent, carlina oxide, on different targets. Firstly, high larvicidal activity against Culex quinquefasciatus, a major lymphatic filariasis and arbovirus vector, for both the essential oil and carlina oxide was detected, with LC50 of 1.31 and 1.39 μg mL-1, respectively. Against Musca domestica the essential oil also was extremely effective (LD50 = 2.74 and 5.96 μg fly−1, on males and females, respectively). Besides, the exposure to a sublethal dose (LD30) led to significant reductions of female longevity (LT50 = 6.7–9.0 days vs. control LT50 = 12.9–13.7 days). The non-target impact of the essential oil was evaluated against Daphnia magna adults, and lower toxicity was detected when compared with cypermethrin. The toxicity of the essential oil was investigated on human cells, showing high cytotoxicity on fibroblasts (NHF-A12, IC50 = 9.4–14.2 μg mL−1). This result should encourage food safety authorities to accomplish a complete toxicological assessment for possible restrictions at the food level. The promising insecticidal activities of C. acaulis essential oil and its main constituent could be an important starting point for the development of novel effective, safe, and eco-friendly botanical insecticides.