Overall repellent effect of plant essential oils on insect choice behaviour: a meta-analysis

Essential oils are considered low environmental impact alternatives for the control of insects harmful to crops and human health. While there is extensive literature on the bioactivities of essential oils on insects, no quantitative syntheses have been conducted to provide a comprehensive overview of their effects. This study aimed to identify general patterns in the effects of essential oils on insect behaviour through meta-analysis, with a specific focus on their choice of food, oviposition sites, and resting sites. We also examined the influence of plant family, insect characteristics, and methodological aspects on these patterns. The results of the meta-analysis provided evidence of an overall repellent effect of essential oils on insects. Insects avoided feeding on food treated with essential oils, as well as laying eggs and staying in areas treated with these compounds. The choice of oviposition and resting sites was significantly influenced by the plant family from which the essential oil was obtained and by the insect order. Also, the insect feeding guild was a significant moderator for the three response variables, with hematophagous and granivorous insects showing stronger avoidance responses. Furthermore, immature insects were more strongly repelled by essential oils compared to adults in their food consumption, and effects of essential oils varied depending on the experimental scale. This study reports, for the first time, global patterns of bioactivity of essential oils on insects and highlights the great potential of these botanicals to be used as repellents in strategies to control agricultural pests and insects of health concern.