Lethal and sub-lethal effects of two botanical nano-insecticides against Liposcelis bostrychophila

Psocids represent a serious pest species in stored products due to their small size and widespread resistance to conventional insecticides. Essential oils (EOs) are promising pest control tools, despite some drawbacks that limit their use under real operating contexts. In response to these challenges, in the last decade, the use of nanotechnology has enhanced EO applications as insecticides. In this context, this study aimed to develop Syzygium aromaticum L. (Clove) and Mentha piperita L. (Mint) EO-nano-emulsions (EO-NEs) with a low amount of co-formulants using the high-pressure microfluidization technique, assessing lethal and sub-lethal effects against Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae). Gas chromatography-mass spectrometry analysis (GC-MS) showed eugenol (76.2%) and menthol (26.69%) as major compounds in clove and mint EOs, respectively. The Dynamic Light Scattering analysis (DLS) revealed excellent physical properties for both EO-NEs with particle sizes ranging in the nanoscale (<250 nm) and good PDI values (<0.25) until 6 months. The lethal effects, assed through residual contact toxicity bioassay, showed high insecticidal activity for clove EO-NE, with estimated lethal doses (LDs) considerably lower compared to mint EO-NE (i.e., LD50 and LD90 of 7.62 and 24.22 μg/cm2 of EO and LD50 and LD90 of 96.72 and 124.79 μg/cm2 of EO, respectively). In addition, mint EO-NE significantly affects the number of produced eggs and their hatchability compared to the negative control treatment. Overall, these findings suggest a potential use of these EO-NEs as sustainable food-stored pest management tools.