Insecticidal activity of nanoemulsions of organophosphorus insecticides against cotton leafworm ( Spodoptera littoralis ) and molecular docking studies

The present study focused on the preparation of nanoemulsions of three organophosphorus compounds (chlorpyrifos-methyl, diazinon, and malathion) as insecticides against larvae of the cotton leafworm ( Spodoptera littoralis ). Oil-in-Water (O/W) nanoemulsions were prepared by the ultrasonication method and characterized by Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) for droplet size analysis. The droplet size values of nanoemulsions were 18.35, 33.05, and 177.20 nm for chlorpyrifos-methyl, diazinon, and malathion, respectively. TEM image and DLS revealed that the droplets were spherical in shape and fall in the nanoemulsion range. The developed formulations were evaluated for insecticidal action against the 4th instar larvae of S. littoralis . Median lethal concentration (LC 50 ) values during a 24 h exposure were 1.27, 2691.12, and 1779.58 mg/L for chlorpyrifos-methyl, diazinon, and malathion nanoemulsions, respectively using a leaf-dip method. However, the LD 50 values were 7.84, 400.41, and 312.67 ng/larva using a topical application. The effect of nanoemulsions on the activity of acetylcholinesterase (AChE), adenosine triphosphate (ATPase) carboxylesterase (CaE), and glutathione S -transferase (GST) was studied. The nanoemulsions showed good toxicity compared to the active ingredient and emulsifiable concentrate (EC) formulations. The protein-ligands docking was also studied and the docking poses showed that the insecticides had a good binding affinity to the active site of the target enzymes. On this basis, these results suggest that O/W nanoemulsion could be applied for the delivery of these insecticides.