Abstract :
[en] Global warming is now widely recognized in the scientific community. These changes are mainly caused by the increase of greenhouse gases, among which the carbon dioxide (CO2) is considered as a major gas. Recent studies showed that abiotic changes will impact the entire ecosystem, and more particularly multitrophic interactions, which are strongly dependent on their environment.
In this study, we hypothezise that an increase of atmospheric CO2 concentration and mean temperature will impact the interactions between a plant, a pest aphid, the mutualistic ant of this aphid and its natural enemy, the hoverfly.
Since organic volatile compounds are involved in these interactions, we first studied the impact of the two abiotic factors on their emission by two plants, Vicia faba and Triticum aestivum and evaluated the capacity of the plant to attract their pests, respectively Aphis fabae and Sitobion avenae. An elevation of temperature, whether or not coupled with CO2 impacted the volatile profiles of these two plant species as well as the concentration of particular compounds of the terpene and alcohol family. These modifications did not impact the foraging behavior of aphids, which indiscriminately located and selected plants grown under ambient or elevated conditions. During infestation, these volatile profiles evolved in the same way under the different climatic conditions.
Secondly, we evaluated the impact of temperature on the mutualistic interaction between the aphid A. fabae and the ant Lasius niger. The mean temperature of 23°C estimated for the end of the 21th century reinforces this interaction, by an increase of ants flows and their collection of honeydew. These positive effects are more attenuated, and the balance of this interaction seems to weakened when one considers one of the most pessimistic climatic models with a 6°C increase (26°C).
Aphid honeydew has a preponderant role in multitrophic interactions. The combination of temperature and CO2 concentration increases the honeydew production as well as its concentration in sucrose and melezitose, which are attractive to ants. On another hand, a high concentration of CO2 had an impact on the volatile profile of the honeydew, but these changes did not affect the oviposition behavior of the hoverfly Episyrphus balteatus, known to use honeydew volatiles, as well as the aphid alarm pheromone, to locate the most suitable sites for oviposition.
Taken together, these results demonstrated that the predicted increase of temperature and CO2 concentration will have a significant influence on multitrophic interactions, but its understanding remains complex and challenging.
