Extended larval development time for aphid parasitoids in the presence of plant endosymbionts

1. Variation in plant chemistry does not only mediate interactions between plants and herbivores but also those between herbivores and their natural enemies, and plants and natural enemies. 2. Endophytic fungi complete their whole life cycle within the host plant's tissue and are associated with a large diversity of plant species. Endophytes of the genus Neotyphodium alter the chemistry of the host plant by producing herbivore toxic alkaloids. 3. Here we asked whether the endophyte-tolerant aphid species Metopolophium festucae could be defended against its parasitoid Aphidius ervi when feeding on endophyte-infected plants. In a laboratory experiment, we compared life-history traits of A. ervi when exposed to hosts on endophyte-infected or endophyte-free Lolium perenne. 4. The presence of endophytes significantly increased larval and pupal development times, but did not affect the mortality of immature parasitoids or the longevity of the adults. Although the number of parasitoid mummies tended to be reduced on endophyte-infected plants, the number of emerging parasitoids did not differ significantly between the two treatments. 5. This shows that the metabolism of individual aphids feeding on infected plants may be changed and help in the defence against parasitoids. An increase in parasitoid development time should ultimately reduce the population growth of A. ervi. Therefore, endophyte presence may represent an advantage for endophyte-tolerant aphid species through extended parasitoid development and its effect on parasitoid population dynamics.