Geranium macrorrhizum, a potential novel companion plant affecting preference and performance of Myzus persicae on sweet pepper

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 efcient
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 efects 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 efects 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.