Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum, to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa, with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.

The combination of a companion plant with a cultivated plant is considered an interesting strategy to reduce pest pressure and, hence, the use of pesticides. Although several plants from the Alliaceae and Lamiaceae families are known to be efficient companion plants against aphid pests, only a few plants of the Geraniaceae family have been studied so far. The aim of this work was to investigate the potential effects of Geranium macrorrhizum as a companion plant on the colonization of sweet pepper (Capsicum annuum, Solanaceae) by the green peach aphid (Myzus persicae). Aphid's orientation behavior, probing behavior and life history traits were assessed on sweet pepper using a host choice preference setup, Electrical Penetration Graph technique and clip-cage laboratory bioassays, respectively. The potential disturbance through mechanical stimulation of geranium leaves was also assessed. The composition of VOCs from G. macrorrhizum leaves was analyzed using SPME technic followed by GC-MS. This study revealed that G. macrorrhizum as a companion plant was intrinsically repellent but not enough to completely mask the attractive odor of the sweet pepper host plant. Moreover, G. macrorrhizum negatively impacted the probing behavior, fecundity and survival rate of M. persicae on sweet pepper. The effects were exacerbated when G. macrorrhizum leaves were mechanically stimulated. This could be due to the greater amount of the main VOCs germacrone and β-elemenone emitted by G. macrorrhizum following mechanical stimulation. Our results bring new insights into the use of novel companion plants to regulate aphid pest populations. Keywords Volatile compounds • Chemical ecology • Electrical penetration graph • Repellent • Geraniaceae Key message• Geranium macrorrhizum as a companion plant can disturb aphid host plant colonization.• Geranium VOCs were repellent but not enough to completely mask the host plant attractive odor. • Geranium VOCs reduced aphid fecundity on the host plant without affecting its probing behavior. • Mechanically stimulated geranium VOCs reduced aphid phloem sap ingestion, survival and fecundity. • These latter effects could be due to the increase in β-elemenone and germacrone emission.