New approach for evaluating the repellent activity of essential oils against storage pests using a miniaturized model of stored-commodity packaging and a wooden transport pallet

Abstract

Essential oils (EOs) are promising compounds for repellent protection of packed commodities or processed food against storage insect pests. Currently, the efficacy of EOs has been tested only when applied to packages, whereas no tests are available for real-world situations in which products are placed on cardboard spacers and transport pallets. Therefore, the aim of this work was to test the effects of placing products on pallets and the treatment of packaging with bergamot essential oil as repellent of storage pests. Due to the size constraint posed by the size of pallets and packaging, miniaturized models were designed and constructed. In this work, we experimentally determined (i) the pest behavioral modification resulting from placing untreated packaging (i.e., without repellent treatment) containing untreated food on a miniaturized pallet vs. placing it on a simulated floor surface and (ii) the repellent effect of bergamot oil applied separately to carton packaging (containing untreated food), wooden pallets or cardboard pallet spacers located between the pallet and packaging on two key storage pests (Sitophilus granarius and Tribolium confusum). The beetle infestation was assessed as a number of beetles in the packaging, and the EO repellency was assessed as number of beetles in the packaging and in the cardboard. The placement of untreated packaging on untreated pallets and spacers decreased packaging infestation by both species in comparison with the placement of products directly on the floor surface. The treatment of various parts of the packaging set (i.e., food packaging, pallet, and cardboard spacer) with bergamot oil had significant repellent activity that was generally more apparent for S. granarius than for T. confusum. The wooden pallet treatment had a greater and longer (i.e., 24 h) repellent effect than the packaging or cardboard spacer treatment on the tested pests. The results showed that the treatment of some parts (such as pallets and cardboard spacers) of the packaging set with essential oils may make it unnecessary to treat primary food/commodity packaging. This may have profound implications for the use and acceptance of essential oils as insect repellents under industrial conditions, since producers may worry about the migration of EOs from the primary packaging to food. Moreover, the miniaturized packaging model presented in this study allowed effective EO repellent testing in large assays in a limited space (e.g., 360 miniaturized model pallets were used in this experiment, and testing this volume of actual Euro pallets would require an area of 346 m2).