Black seed and rosemary nanoformulations as green insecticides for the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae)

The development of nano-insecticides has attracted much interest in the last decade because it has the potential to result in an alternative pest-management strategy and also reduce the risk of chemically based insecticides. Herein, native rosemary (Rosmarinus officinalis) and black seed (Nigella sativa) oils were utilized for preparing their nanoemulsions by spontaneous emulsification method in the presence of tween 80 as a structure-directing agent. The prepared nanoemulsions were explored for granary weevil, Sitophilus granarius (L.), adults control and compared with their oils. Within the typical droplet sizes of 100 and 224 nm, both rosemary and black seed nanoemulsions were found to be physically and thermodynamically stable. The insecticidal activity of the nanoemulsions was higher than that of the crude oils. After 24 h of exposure, the LD50 values of rosemary and black seed nanoemulsions were estimated to be 102.56 and 35.08 mu g/g, respectively, compared to 188.95 and 210.09 mu g/g of their oils. These results revealed that the droplet size and chemical composition of the nanoemulsion are the significant factors that affect their toxicity. Surprisingly, the nanoemulsions had no effect on seed germination at LD50 or even LD99. The utilization of such nanoformulations might open up a new avenue for ecofriendly pest control that is not damaging to humans or the environment, as well as a growing agricultural economy. Practical Application The loss of cereals in postharvesting is one of the major challenges in the world because up to 50% of harvested grains might be destroyed. The intensive usage of chemicals caused harmful effects on humans and the environment. Thus, we prepared rosemary and black seed nanoemulsions and applied them for the grain weevil, S. granarius, control. The results showed superior toxicological efficacy without any effects on seed germination compared with their native oils. Such green strategy could be used instead of chemical insecticides to be environmentally safe for animals and humans.