Larvicidal and Antifeedant Effects of Copper Nano-Pesticides against Spodoptera frugiperda (J.E. Smith) and Its Immunological Response

SIMPLE SUMMARY: The polyphagous agricultural pest Spodoptera frugiperda (J.E. Smith) has a high level of chemical pesticide resistance. This study’s objective is to create and assess the effectiveness of CuO NPs (copper oxide nanoparticles) with a variety of tests against S. frugiperda for larvicidal, antifeedant, immunological, and enzymatic activities. Energy dispersive X-ray (EDaX) analysis and a scanning electron microscope (SEM) were used to analyze copper nanoparticles for the identification of physical and chemical properties. The CuO NPs demonstrated high larvicidal and antifeedant activity. The CuO NPs treatment significantly reduced the number of larval hemocytes 24 h after treatment when compared to the control; hemocyte counts and sizes also varied. The levels of larval acetylcholinesterase enzyme levels were decreased with dose-dependent activity after 24 h of treatment with CuO NPs. The current research conclusively shows that CuO NPs have remarkable larvicidal antifeedant activity. ABSTRACT: This study aimed to synthesize and evaluate the efficacy of CuO NPs (copper oxide nanoparticles) with varying test concentrations (10–500 ppm) against larvicidal, antifeedant, immunological, and enzymatic activities against larvae of S. frugiperda at 24 h of treatment. Copper nanoparticles were characterized by using a scanning electron microscope (SEM) and energy dispersive X-ray (EDaX) analysis. The EDaX analysis results clearly show that the synthesized copper nanoparticles contain copper as the main element, and the SEM analysis results show nanoparticle sizes ranging from 29 to 45 nm. The CuO NPs showed remarkable larvicidal activity (97%, 94%, and 81% were observed on the 3rd, 4th, and 5th instar larvae, respectively). The CuO NPs produced high antifeedant activity (98.25%, 98.01%, and 98.42%), which was observed on the 3rd, 4th, and 5th instar larvae, respectively. CuO NPs treatment significantly reduced larval hemocyte levels 24 h after treatment; hemocyte counts and sizes changed in the CuO NPs treatment compared to the control. After 24 h of treatment with CuO NPs, the larval acetylcholinesterase enzyme levels decreased with dose-dependent activity. The present findings conclude that CuO NPs cause remarkable larvicidal antifeedant activity and that CuO NPs are effective, pollution-free green nano-insecticides against S. frugiperda.