Bioefficacy of Essential Oil Based Nano Insecticidal Formulations against Anopheles stephensi and Culex quinquefasciatus

Abstract

As the mosquitoes are vectors of numerous deadliest diseases, they continue to be a major cause of morbidity and mortality around the world. Therefore, the current study aims to evaluate the larval toxicity of selected essential oils (Argemone mexicana, Azadirachta indica, Citrus limetta, C. limon and C. reticulata) and formulate their safer and efficient phyto-nanoemulsions against Anopheles stephensi and Culex quinquefasciatus. According to the phytochemical and GC-MS analysis, selected essential oils indicated the presence of alkaloids, anthraquinones, flavonoids, tannins, terpenes, quercetin, argemonine, linalool, transand#8210;phytol, caryophyllene oxide, viridiflorene, Dand#8210;limonene, and#946;and#8210;terpinene, citral, tertand#8210;butylbenzene, terpinenand#8210;4and#8210;ol and 3and#8210;carene, sylvestrene, and#946;and#8210;pinene and and#947;and#8210;terpinene as the major phytocompounds. Among all the selected plants, Citrus limetta and C. reticulata were showed significant larvicidal bioefficacy followed by C. limon, Argemone mexicana and Azadirachta indica against Anopheles stephensi and Culex quinquefasciatus. In addition, the combined larvicidal of most effective essential oils bioefficacy revealed that the combinations, 1:1 and 1:2 ratios demonstrated the synergism and 1:3 showed antagonism. Furthermore, the prepared nanoemulsions (1:1, 1:1.5 and 1:2 EO:S) had spherical and uniformly distributed nano-sized droplets with low PDI values. However, the smallest size of droplets were recorded in NEL-2 (1:1.5) and NEP-2 (1:1.5) as 15.64 and 13.05 nm, respectively. They both were stable even after 90 days of preparation and exhibited excellent larvicidal bioefficacy against target organisms. Moreover, these two optimum nanoemulsions inhibited the activities of acetylcholinesterase, carboxylesterases, glucose, lipids and proteins while the activities of glutathioneand#8210;Sand#8210;transferase, acid and alkaline phosphatases were increased in larvae after the exposure. The morphological analysis revealed that the treated larvae have degraded cuticle, degenerated eyes, head and mouth parts, collapsed abdominal segments and blocked siphon. In non-target bioassay, there was negligible efficacy recorded against snails and tadpoles after the exposure of NEL-2 and NEP-2. The residual analysis indicated that the nanoemulsions efficiently released the active constituents and were effective as larvicides. According to the seed germination bioassay, the nanoemulsions (NEL-2 and NEP-2) did not significantly reduce the germination and growth of wheat and barley seeds. newline