Novel entomotoxic nanocides for agro-chemical industry

In recent years, pest management scientists are reappraising the use of inert dusts as alternative insecticides because of several growing problem of the conventional insecticides like cumulative environmental pollution, increasing insect resistance to them etc. The naturally occurring amorphous micron sized silica (Diatomaceous Earth), derived from fossil phytoplankton has gained enormous popularity as a physically active insecticide in the temperate countries. Here we investigated and compared the insecticidal efficacy of surface functionalized amorphous silica nanoparticle (SNP) with micron sized silica “FossilShield90.0s” on tropical army worm Spodoptera litura. S. litura is a polyphagous pest which attacks a number of crops and vegetables. All micron and nano sized silica were applied on the second instar larvae of S. litura at four dose rates with proper control. It was found that all SNPs were much more effective than “FossilShield90.0s”. Especially, hydrophilic SNP could kill all the larvae within 24 hours of the treatment. In vitro toxicity of SNPs was evaluated on MRC-5 cells with the help of water soluble tetrazolium (WST-1) and lactate dehydrogenase (LDH) assays. Unlike conventional insecticides, SNP kills the insects by causing damage to their cuticular water barrier. Insects lose water through their damaged cuticle and die because of desiccation. As this nanocide is physically active, insects are unlikely to develop resistance against it. United States Department of Agriculture has approved amorphous silica as bio safe.