Sargassum wightii-synthesized ZnO nanoparticles reduce the fitness and reproduction of the malaria vector Anopheles stephensi and cotton bollworm Helicoverpa armigera

Helicoverpa armigera Hubner is an important polyphagous agricultural insect pest, highly mobile, with a worldwide distribution. In India, it causes substantial losses to cotton, legumes, cereal and vegetable crops. Malaria is caused by parasites from the genus Plasmodium that are transmitted by female anopheline mosquitoes. Anopheles stephensi Liston is the leading vector of malaria in India, parts of Asia and the Middle East. In this research, we investigated the efficacy of green-synthesized zinc oxide nanoparticles (ZnO NPs) fabricated using the brown macroalga Sargassum wightii Greville ex J.Agardh. The formation of ZnO NPs was confirmed by surface Plasmon resonance band illustrated in UV–vis spectrophotometry. ZnO NP were characterized by XRD, SEM, EDX and FTIR analyses. Low doses of S. wightii extract and ZnO NP showed larvicidal and pupicidal toxicity on A. stephensi and H. armigera. LC₅₀ of ZnO NP ranged from 4.330 (larva I) to 7.430 ppm (pupa) for An. stephensi, and from 12.278 (larva I) to 20.798 ppm (pupa) for H. armigera. Both S. wightii extract and ZnO NP strongly reduced longevity and fecundity of An. stephensi and H. armigera. In food utilization experiments, the S. wightii extract and ZnO NP reduced food consumption of H. armigera individuals. Nutritional indices declined significantly, while the larval approximate digestibility was significantly higher post-treatment with 25 ppm of ZnO NP and 250 ppm of S. wightii extract. Concerning non-target effects, in standard laboratory conditions the predation efficiency of guppy Poecilia reticulata was 66.28% and 55.36% against I and II instar larvae of An. stephensi, respectively. In a ZnO NP-contaminated environment, fish predation was boosted to 86.75% and 74.12%, respectively. Overall, the current approach adopted here contributes to control and adaptively manage resistance to other available insecticides in field populations of H. armigera and An. stephensi.