Development of Nanocomposite Bioactive Diffusion Films (BDFs) Combined With Gamma Irradiation for Control of the Rice Weevil Sitophilus oryzae , a Stored Product Pest

The fumigant toxicity of 6 essential oils (EOs) (Mediterranean, Southern, citrus, cinnamon, Asian, and savory thyme), 2 citrus extracts (CEs: organic OCE and natural NCE), and 2 active formulations (microfluidized nanoemulsions AF-1 and AF-2) was investigated for control of rice weevil (Sitophilus oryzae), a stored product pest. In bioassays, AF-1 and AF-2 at 0.6 µL/mL exhibited higher insecticidal efficacy compared to single EOs and CEs after 72 h of exposure. AF-2 showed higher acetylcholinesterase enzyme inhibition in rice weevils than AF-1. Oil-in-water nanoemulsions (NEs) of AF-1 and AF-2 were prepared by microfluidization, resulting in a decrease in droplet size (DS) from 232 to 116 nm and 230 to 40 nm, and an increase in encapsulation efficiency (EE) from 30% to 77% and from 11% to 79% respectively. To exploit the insecticidal attributes of these NEs, 6 nanocomposite bioactive diffusion films (BDFs) were prepared based on chitosan (CH), poly(butylene adipate-co-terephthalate (PBAT), or polylactic acid (PLA), all reinforced with cellulose nanocrystals (CNC), and containing either AF-1 or AF-2. Films were evaluated as diffusion devices in bags of rice infested with weevils. CH films induced the highest insect mortality (78%-83%) after 14 days, compared to 6% in controls. Gamma irradiation at 200 Gy alone caused 62% mortality, which increased to 82%100% after combination with the BDFs after 14 days. The presence of CNC in BDFs reduced the % release of bioactive NEs by 12%-27% compared to the films without CNC. PRACTICAL APPLICATIONS: Nanocomposite BDFs developed in this study could be applied as diffusion devices of insecticidal natural compounds for the control of rice weevils in packaged rice. The active formulations (AF-1 and AF-2 based on nanoemulsions of CEs and EOs), combined with low-dose irradiation treatments, could be used in the food industry for controlling insect proliferation in the sector of stored cereals.