How Environmental Fluctuations Affect Volatile Emissions from Basil and French Marigold and their Consequences on the Fecundity of the Green Peach Aphid on Pepper Plants.

By releasing volatile organic compounds (VOCs), French marigold and basil have been shown in the laboratory to disrupt the fecundity of the green peach aphid, Myzus persicae. Thus, they can be potential companion plants (CP) for target crops. To determine whether, fluctuating environment may impair their efficacy, three runs were carried out successively from March to June, during which we monitored the VOC emissions and the aphid population dynamics on pepper plants interplanted in different tunnels with basil, French marigold or pepper plants only. The presence of basil significantly decreased the daily fecundity and the intrinsic rate of natural increase of the M. persicae population, increasing the doubling time of the population, French marigold was less efficient. When expressed per degree days, basil and to a lesser extend French marigold significantly reduced aphid fecundity whatever the run, despite the fact that their VOCs blend emission differed. The volume of VOCs emission from CPs changed between runs, during the run, and at a daily scale. Most VOC emissions were significantly correlated with temperature over a 24 h VOC sampling period. These data support the hypothesis that the effectiveness of the olfactory message delivered by CPs can accommodate a variable production volume or composition. The involvement of a particular VOC or mixture of VOCs is difficult to establish, although the presence of (E)-β-farnesene (which could have a direct repellent effect on aphid) or eugenol (which could mediate plant-plant interaction and reduce pepper plant suitability) may be highlighted. This study confirms the efficacy of interplanting basil with pepper in tunnels to reduce M. persicae fecundity despite fluctuating temperatures that modify basil volatile blend.