Preparation, Characterization, Efficiency of Nano-emulsion Chlorpyrifos and Methomyl and Determination of their Residues in Pepper Fruits

The current study aimed to prepare nano-emulsions of chlorpyrifos and methomyl insecticides as well as evaluate their efficiency against cotton leafworm (Spodoptera litoralis) compared with their commercial formulation under laboratory conditions. Also, residues in pepper fruits were determined after field application. Results revealed that the resultant particles of the chlorpyrifos 10% nano-emulsion particle size distribution ranged between 50 and 500 nm; with an average particle size of 187.3 nm. In the case of methomyl nano-emulsion, the resultant particle size distribution was ranged between 30 and 2000 nm with an average particle size of 336.4 nm. The results revealed that the nano-formulations of both insecticides were more toxic and effective against the 4th instar larvae than their commercial formulations. According to the LC50 values, the toxicity of the chlorpyrifos and methomyl 10% nano-emulsion were 1.71 and 2.1 times higher toxic than that of chlorpyrifos 48% EC and methomyl 90% SP, respectively. The sub-lethal doses (LC25 and LC10) of both nano and commercial formulations of chlorpyrifos and methomyl affected pupation % and adult emergence%. The highest effect was observed in larvae treated with LC25 of nano-emulsion of both insecticides. Moreover, after 15 days of fruit spray with the two tested insecticides and their nano emulsions, the lost amount of chlorpyrifos EC and nano-emulsion forms reached 96.5 and 99.2 % of the initial deposit, respectively. In contrast, it reached 0.08 ppm of Methomyl SP (loss % was 98.8), and no residues were detected in methomyl nano-emulsion-treated fruits. This means that the nano-emulsion formulations of both insecticides were faster degradable and more effective against S. litoralis larvae than their commercial formulations. Accordingly, these formulations may improve efficiency and reduce the residues that may decrease the adverse impacts on the environment and non-target organisms.