Saponaria officinalis-synthesized silver nanocrystals as effective biopesticides and oviposition inhibitors against Tetranychus urticae Koch

Green-fabricated nanoparticles have been mainly tested on mosquito and tick vectors, while no information are available about their toxicity against phytophagous mites. Therefore, here it was determined whether Ag nanoparticles with acaricidal activity could be synthesized using the Saponaria officinalis root extract. Size, shape and crystalline structure of the nanoparticles were described. Furthermore, the toxicity of S. officinalis extract vs. S. officinalis-fabricated Ag nanoparticles was studied, comparing their activity on eggs, larvae and adults of two-spotted spider mite Tetranychus urticae. The impact of both treatments on T. urticae oviposition was investigated. Both the S. officinalis root extract and the nanoparticles showed a very good acaricidal efficacy. Ag nanoparticle LC50 was 1.2 g L−1 (LC90 = 2.8 g L−1), significantly less if compared with the root extract alone (LC50(90) = 7.8 (11.9)g L−1). Adults of T. urticae showed the lowest sensitivity, with LC50 of 6.1 and 19.9 g L−1 for nanoparticles and the aqueous root extract, respectively. Both treatments showed high ovicidal toxicity with LC50 of 3.1 and 13.8 g L−1 for the nanoparticles and aqueous root extract, respectively. Treatment spray residues also caused significant inhibition of oviposition in females of T. urticae with EC50 estimated as 1.4 g L−1, a value significantly lower, if compared with the extract alone (EC50 = 6.1 g L−1). No phytotoxicity of both treatments was observed in short-term tests. S. officinalis root aqueous extract is used by food and cosmetic industries, thus it can be considered a safe option for plant protection. In addition, the fabricated AgNP also seem highly promising as they showed high biological efficacy, and the production method is relatively simple and cheap.