Pathogens and other parasites can have profound effects on biological communities and ecosystems. Here we explore how two strains of a plant virus – Barley Yellow Dwarf Virus, BYDV – influence the foraging performance and fecundity of two aphid species: Rhopalosiphum maidis and R. padi. We found that pre-inhabitation by R. padi on plants facilitates the subsequent foraging of conspecifics and R. maidis. Without the virus, the occurrence of facilitation is asymmetric because it depends on the order of species arrival. However, with virus we found facilitation irrespective of the order of species arrival. Furthermore, the virus also boosted the fecundity of both aphids. Analyses of nutrient content of virus-free and virus-infected plants show significant increases of essential amino acids, sterols, and carbohydrates. Such nutrient increases appear to underlie the facilitative interactions and fecundity of aphids on virus-infected plants. Our experiments demonstrate that the virus dramatically increases the food consumption and fecundity of aphids through intra and interspecific trophic facilitation, resulting in processes that could affect community organization.
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