BACKGROUND Intercropping companion plants (CPs) with horticultural crops could be an eco‐friendly strategy to optimize pest management. In this research, volatile organic compounds (VOCs) emitted by some CPs were investigated for their repellent properties towards the green peach aphid (Myzus persicae Sulzer). The aim of this study was to understand the modes of action involved: direct effects on the aphid and/or indirect effects via the host plant (pepper, Capsicum annuum L.). RESULTS We identified two promising repellent CP species: the volatile blend from basil (Ocimum basilicum, direct repellent effect) and the mixture of (or previously intercropped) C. annuum plants with Tagetes patula cv. Nana (indirect effect). This effect was cultivar‐dependent and linked to the volatile bouquet. For the 16 compounds present in the O. basilicum or T. patula bouquets tested individually, (E)‐β‐farnesene, and eugenol reported good repellent properties against M. persicae. Other compounds were repellent at medium and/or highest concentrations. Thus, the presence of repellent VOCs in a mixture does not mean that it has a repellent propriety. CONCLUSION We identified two promising repellent CP species towards M. persicae, with a likely effect of one CP's VOCs on the host plant repellency and highlighted the specific effectiveness of VOC blends. © 2018 Society of Chemical Industry

1 Previous studies have shown that rosemary (Rosmarinus officinalis L.) can serve as a companion plant to control Myzus persicae (Sulzer) because of the repellent effect of certain volatile organic compounds (VOCs) that it emits. In the present study, we investigated which of five clones of rosemary may reveal a repellent effect on M. persicae and aimed to determine the possible VOCs involved. 2 Analyses of the mixtures of VOCs released by the different clones revealed the presence of 15 main components. However, each clone was characterized by a specific volatile profile showing the existence of marked chemical variability. 3 By testing the identified VOCs individually, using a dual-choice olfactometer, we observed that five volatiles had a significant repulsive effect on M. persicae: bornyl acetate, camphor, -terpineol, terpinene-4-ol and geranyl acetone. In addition, only one clone of rosemary elicited a significant repulsive action. 4 Nevertheless, all of the tested clones released compounds that are repellent to the aphid when tested individually. Therefore, the emission of individual volatiles by a rosemary plant is not sufficient to elicit a repellent effect. 5 The concentration, proportion and even the association/synergy of VOCs in the released olfactory bouquets can probably explain these contrasting results and are worthy of additional exploration in future studies.

BACKGROUND The association of crops of value with companion plants could be one of the strategies to reduce the harmful effects of pests. We hypothesize that volatile organic compounds (VOCs) emitted by some aromatic plants may negatively impact M. persicae, disturbing its feeding behavior and consequently its reproduction. RESULTS VOCs emitted from six potential companion plant species affected the reproduction of M. persicae feeding on pepper plants, Capsicum annuum. Reproduction of M. persicae was reduced when exposed to VOCs from leaves of Ocimum basilicum and flowers of Tagetes patula. Thus, species and phenology of the companion plant can influence the effect. The VOCs from O. basilicum and T. patula also reduced phloem feeding by the aphids based on electropenetrography (EPG). CONCLUSION The reduced fecundity of M. persicae could be linked to aphid feeding disruption provoked by the VOCs emitted by O. basilicum in the vegetative stage or T. patula cv. Nana in the flowering stage. © 2020 Society of Chemical Industry

The repellent properties of volatile organic compounds (VOCs) emitted by several companion plant species (CPs) were tested on the rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), in a new dynamic tubular olfactometer connected to a dynamic plant chamber. This device allows a rapid and direct measurement of the repellency of whole plants on an aphid population. The VOC production, correlated to the number of plants in the chamber, was determined, and the VOC concentration in the emitted blend was evaluated to establish a causal link with the aphid response. Three species showed strong repellency properties to D. plantaginea: peppermint, Mentha piperita L., lavandin, Lavandula × intermedia Emeric ex Loisel., and rosemary, Salvia rosmarinus Schleid. (all Lamiaceae). In addition, tests on various rosemary chemotypes showed that the repellency could vary within the chemotype. The developed device revealed a classification of the tested CPs according to the analyzed VOCs and a link between the repellency index (RI) and the presence of certain VOCs. Thus, eucalyptol, β‐ocimene, allo‐ocimene, piperitone, l‐menthone‐1, and l‐menthone‐2 were associated with the highest RIs, although not all of them were identified as repellents. Thus, the repellent effect of a CP results primarily from the produced olfactory mixture in which the presence and quantity of particular VOCs would modulate the repellent efficiency.