Preparation of nanosilica from sugarcane bagasse ash for enhanced insecticidal activity of diatomaceous earth against two stored-products insect pests

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.

Nanomaterials for Postharvest Management of Insect Pests: Current State and Future Perspectives

Globally, between one quarter and one-third of total grains produced each year are lost during storage mainly through infestation of insect pests. Among the available control options such as chemical and physical techniques, fumigation with aluminum phosphide (AlP) is so far considered the best control strategy against storage insect pests. However, these insect pests are now developing resistance against AIP due to its indiscriminate use due to non-availability of any effective alternative control option. Resistance to AIP among storage insect pests is increasing, and its inhalation has shown adverse effects on animals and human beings. Nanotechnology has opened up a wide range of opportunities in various fields such as agriculture (pesticides, fertilizers, etc.), pharmaceuticals, and electronics. One of the applications of nanotechnology is the usage of nanomaterial-based insecticide formulations for mitigating field and storage insect pests. Several formulations, namely, nanoemulsions, nanosuspensions, controlled release formulations, and solid-based nanopesticides, have been developed with different modes of action and application. The major advantage is their small size which helps in proper spreading on the pest surface, and thus, better action than conventional pesticides is achieved. Besides their minute size, these have no or reduced harmful effects on non-target species. Nanopesticides can therefore provide green and efficient alternatives for the management of insect pests of field and storage. However, an outcry against the utilization of nano-based pesticides is also revealed. It is considered by some that nano-insecticides may also have hazardous effects on humans as well as on the environment. Due to limited available data, nanopesticides have become a double-edged weapon. Therefore, nanomaterials need to be evaluated extensively for their large-scale adoption. In this article, we reviewed the nanoformulations that are developed and have proved effective against the insect pests under postharvest storage of grains.