Bioactivity and qualitative analysis of some essential oils from mediterranean plants against stored-product pests: evaluation of repellency against Sitophilus zeamais Motschulsky, Cryptolestes ferrugineus (Stephens) and Tenebrio molitor (L.)

Essential oils extracted from bay laurel (Laurus nobilis), bergamot (Citrus bergamia), fennel (Foeniculum vulgare) and lavandin (Lavandula hybrida) were tested for repellency against Sitophilus zeamais and Cryptolestes ferrugineus adults and Tenebrio molitor larvae. Composition of L. nobilis essential oil included large amounts of monoterpenes, mainly oxygenated derivatives, while in C. bergamia essential oil limonene was the main compound followed by linalyl acetate and g-terpinene and linalool. In lavandin oil there was a prevalence of linalool and linalyl acetate, while phenyl propanoids were the main compounds detected in fennel essential oil. Two kinds of bioassays were performed: filter paper tests, carried out in Petri dishes on all three coleopteran species and tests on treated kernels carried out only on S. zeamais adults. In filter paper bioassays, essential oils showed different activity: on S. zeamais, fennel after 3 h of exposure and bergamot after 24 h exerted the highest repellency, similar results were obtained for C. ferrugineus, but lavandin also showed good repellent activity, while for T. molitor larvae bay laurel was the most effective repellent. Repellency tests on kernels against S. zeamais adults suggested that bergamot and lavandin were the most efficient oils. Even if laboratory bioassays are only the first step towards use of essential oils in practical applications, these substances do represent a possible alternative to chemical insecticides in some market niches