The aphid facultative symbiont Serratia symbiotica influences the foraging behaviors and the life-history traits of the parasitoid Aphidius ervi

Aphids (Hemiptera: Aphididae) maintain intimate relationships with a variety of symbiotic bacteria that can be important drivers of their evolutionary ecology. In addition to the obligate endosymbiont Buchnera aphidicola, aphids may harbor a series of facultative symbionts that can affect their physiology, as they may be involved in heat resistance, nutrition, reproduction and defense against parasitoids. Since the presence of facultative symbionts in aphids can be disadvantageous for parasitoids, it is hypothesized that these insects have developed strategies to adjust their responses to the presence of these bacteria. In this study, experiments were conducted to determine whether the presence of the facultative symbiont Serratia symbiotica in the pea aphid Acyrtosiphum pisum affects the development and the life-history traits of the generalist parasitoid Aphidius ervi (Hymenoptera: Braconidae). Behavioral assays were also performed to determine whether the infection status of host aphids influences the foraging behavior of the parasitoids. It was showed that the presence of S. symbiotica had negative effects on the development and the life-history traits of emerging parasitoids. It was found that parasitoids preferentially orient themselves to uninfected aphid hosts, probably through chemical clues, and that they adjust their foraging behavior by investing more time in patches composed of uninfected aphid hosts. In light of these results, it is assumed that the presence of S. symbiotica alters host aphid quality, which in turn influences the choice of the female parasitoids for oviposition as well as the quality of the emerging parasitoids. This study highlights the ability of parasitoid wasps to modify their perception and behavior towards aphids infected with facultative symbionts and how these microorganisms interfere with host-parasite relationships.