Food nutrition and facultative endosymbiont modulate dietary breadth of a polyphagous aphid.

While host plants and endosymbionts have been implicated in influencing dietary breadth in polyphagous herbivores, the underlying mechanism remains vague. In this study, we focused on the food nutrition and nutrition provision of endosymbionts to elucidate the determination of dietary breadth in a polyphagous aphid Aphis gossypii. Our findings demonstrated that high sugar and riboflavin presence in food decreased aphid fitness, while Arsenophonus infections improved aphid performance. Aphids collected from cotton could not use cucumber whether they were infected with Arsenophonus or not, signifying a distinct specialization toward cotton. Further, both the Arsenophonus-infected and free aphids fed on artificial diet varying in sugar titer failed to utilize cucumber. However, Arsenophonus-free aphids attained the ability to utilize cucumber after feeding on the riboflavin-free diet, but not on the riboflavin-containing diet, indicating riboflavin and Arsenophonus-absent expansion in dietary breadth. Notably, up-regulated expression of riboflavin synthase genes of the obligated symbiont Buchnera aphidicola was detected in the Arsenophonus-infected aphids which may provide more riboflavin. Arsenophonus promoting riboflavin synthesis in the obligated symbiont B. aphidicola and riboflavin ingestion enhancing host specialization of aphids to cotton modulate dietary breadth of A. gossypii.