Silica and mesoporous silica nanoparticles display effective insecticidal effect and augment plant defense responses

The polyphagous insect pest, Spodoptera litura displays insecticide resistance that requires new control tactics. In this context, inorganic silica nanoparticles (SiNPs) and mesoporous silica nanoparticles (MSNPs) were studied for their insecticidal activity and their effects on the plant defense responses. The synthesized silica (SiNPs,160 nm size) and mesoporous silica (MSNPs,100 nm size) nanoparticles showed high insecticidal effect of against S. litura larvae with 73.0 and 80.0 % mortalities, respectively at low nanoparticles concentration (1 μg). Administration of NPs by feeding enhanced the larval gut uptake and caused a significant ∼14.9- to 12.7-fold reduction in lactate dehydrogenase activity for SiNPs and MSNPs, respectively. Efficient uptake of fluorescent NPs was illustrated in columnar larval gut cells. Feeding of SiNPs and MSNPs led to a significant reduction in larval weight (2.9- and 3.4-fold, respectively) due to their antifeedant effect which was positively correlated to larval mortalities. Both NPs exhibited negligible cytotoxicity in vitro. Furthermore, application of rhodamine B fluorescence-tagged NPs on soyabean leaves showed NPs presence on the leaf surfaces and were not internalized by the leaf. Moreover, the electromechanical plant responses to NPs application displayed increased localized signal durations (>2-fold). Additionally, SiNPs and MSNPs treatments significantly upregulated the 12-oxophytodienoate reductase plant jasmonic acid defense pathway gene expression (2.7- and 1.4-fold, respectively) that led to enhanced jasmonic acid contents. Application of SiNPs and MSNPs at low concentrations achieved insecticidal effect against S. litura and enhanced the plant defense responses against pest. Silica nanoparticles have potential in safe and effective management of S. litura.