Prefatory in silico studies and in vitro insecticidal effect of Nigella sativa (L.) essential oil and its active compound (carvacrol) against the Callosobruchus maculatus adults (Fab), a major pest of chickpea

To help discover a reasonable and eco-friendly insecticide, we undertook a study on the insecticidal potential of carvacrol and essential oils extracted by hydrodistillation using a Clevenger apparatus from the plant species Nigella sativa seeds essential oils of Nigella sativa (EONS) on Callosobruchus maculatus adults. Several tests including contact toxicity, repellent effect, topical contact test, and inhalation effect were conducted. Adults of C. maculatus have been exposed to the toxic effects of different concentrations of these essential oils as well as with carvacrol. The results obtained showed that both EONS and carvacrol exhibited a moderate repellent effect (class II) on C. maculatus adults. EONS showed the highest toxicity by inhalation test, with an LD50 of 13.386 and an LD95 of 33.186 μL/cm2, compared to carvacrol (LD50 = 21.509 and LD95 = 38.877 μL/cm2). The EONS by contact test exhibited more toxic effects, with an LD50 of 23.350 µL/100 g and an LD95 of 45.315 µL/100 g, compared to carvacrol (LD50 = 27.853 µL/100 g and LD95 = 45.184 µL/100 g). For the topical contact test results, carvacrol was more toxic, with an LD50 of 3.915 and an LD95 of 7.696 µL/mL, compared to EONS (LD50 = 14.509 and LD95 = 25.516 µL/mL). The high toxicity of EONS can be explained by the presence of 25.8% of o-cymene, 8.53% of cyclofenchene, and 7.71% of beta-pinene, as well as 4.6% of carvacrol, in its chemical composition. Unmitigatedly, these data suggest that the essential oils of N. sativa may present a raw material for the development of new bio-insecticidal products against C. maculatus, one of the main pests of stored foodstuffs.