Polymeric nanoparticles improve lethal and sublethal effects of essential oils and pyrethroids toward the rice weevil and the cigarette beetle

The rice weevil ( Sitophilus oryzae L.) and the cigarette beetle ( Lasioderma serricorne F.) are primary and secondary insect pests that cause significant damage to stored grains and commodities. The goal of this study was to evaluate the physicochemical properties and insecticidal activity of Origanum vulgare (L.) (OV) and Laurus nobilis (L.) (LN) essential oils (EOs) in polymeric nanoparticles (PNs) prepared using the melt dispersion technique with polyethylene glycol (PEG 6000) as the matricidal material. In PNs, the monocyclic monoterpenes were retained in high proportions after encapsulation. Physicochemical analyses revealed that OV and LN PNs had mean sizes of 295 and 429 nm, respectively, with a loading efficiency of almost 90%, and a polydispersity index ≤ 0.25 (monodisperse samples). Against Sitophilus oryzae , only OV PN significantly enhanced the lethal effect of EO, whereas on L. serricorne, both PNs. It was demonstrated that, on both pests, OV EO and its PNs increased their sensitivity to pyrethroids, whereas LN oil and their PNs promote this effect only on S. oryzae . The PNs of OV and LN altered the nutritional physiology and behavior variables of both stored product pest and prolonged the repellent effect of the EOs on S. oryzae and L. serricorne up to 60 and 48 h. Ecotoxicity bioassays demonstrated that OV and LN EOs and their PNs were harmless to terrestrial non-target organisms and had slight negative effects on aquatic non-target organisms. Finally, PNs did not affect viability of primary osteoblast cells.