Endemic Andean plants against food-stuff insect pest

Tropical Andes, because of the exceptional number of endemic plants, have been classified as a hyper-hot spot for biodiversity and they represent an extraordinary source of yet undiscovered bioactive compounds. In fact, many of these plants are used in the local traditional medicine by the population, as well as to control fastidious insects. The properties of many of these plants, as well as their smell, are due to their essential oils, volatile substances produced either as a protection against phytophagous insects and to attract pollinators. Several studies have reported the toxicity and repellent activity of Andean plants essential oils against insects. However, to our knowledge, no information is available about their attractiveness. In this work, we analyzed the chemical composition and assessed the repellency and attractiveness of the essential oils of the Andean endemic plants Aloysia citrodora (Verbenaceae), Bursera graveolens (Bursedraceae), and Buddleja globosa (Scrophulariaceae) against the main food-stuff insect pests Rhizopertha dominica (Coleoptera: Bostrichidae) and Tribolium confusum (Coleoptera: Tenebrionidae) by area preference tests. The results showed that the tested essential oils have high repellency rates at high concentrations whilst, on the contrary, they are attractive to the insects at the lowest concentrations. Such results, beside confirming that tropical Andes plants are a valuable unexploited source of bioactive substances, indicate that the use of essential oils as repellent for the protection of the food should be evaluated carefully, also taking into account that both i) concentration changes in time due to their volatility and ii) their compositional variation due to volatilization can cause dramatic changes of bioactivity of the essential oils against insect pests.