Trophic cascades initiated by fungal plant endosymbionts impair reproductive performance of parasitoids in the second generation

Abstract

Variation in plant quality can transmit up the food chain and may aVect herbivores and their antagonists in the same direction. Fungal endosymbionts of grasses change the resource quality by producing toxins. We used an aphid-parasitoid model system to explore how endophyte
eVects cascade up the food chain and inXuence individual
parasitoid performance. We show that the presence of an endophyte in the grass Lolium perenne has a much stronger negative impact on the performance of the parasitoid Aphidius ervi than on its aphid host Metopolophium
festucae. Although the presence of endophytes did not
inXuence the parasitism rate of endophyte-naïve parasitoids
or their oVspring’s survival to adulthood, most parasitoids
developing within aphids from endophyte-infected plants did not reproduce at all. This indicates a delayed but very strong eVect of endophytes on parasitoid performance, which should ultimately aVect plant performance negatively by releasing endophyte-tolerant herbivores from top-down
limitations.