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Most insect herbivores specialize on a few host plants; however, there are a minority of highly generalized species capable of feeding on hundreds of hosts. Generalism could emerge as a property of the species as a whole, while individuals would still exhibit greater specialization at more specific organizational levels. Yet, we lack studies with generalist insect herbivores directly testing this prediction. Here, we test if the highly generalized fall webworm (Hyphantria cunea) maintains its broad diet through specialization at the population, maternal genotype, or individual level. We reared two populations and multiple matrilines on either a static or rotating diet of four host plants. We found that both populations survived and pupated on all hosts, suggesting population-level generalization. We found evidence for generalization at the genotype level, as maternal genotypes did not vary in performance rankings across host plants. Finally, we found generalism at the individual level, as individuals reared on a rotating diet had no difference or showed intermediate performance to those reared on static diets. Overall, we found support for the maintenance of generalism across all levels, suggesting that generalist species need not be locally specialized to maintain their extremely broad diet. 

Abstract Fall webworm (Hyphantria cunea) is a widespread, highly polyphagous moth in the family Erebidae, whose native range spans much of North America and invasive range includes Asia and Europe. The species uses over 600 plant species as a larval host, making it among the most generalized insect herbivores described. Its variable host use, wide range, and genetic diversity make fall webworm an attractive emerging model system for the study of diet breadth, but studies have been limited by the lack of a high-quality annotated reference genome. Here we report an annotated, chromosome-scale genome of much improved continuity and completeness over the previously available unannotated fall webworm reference genome. We used PacBioHiFi long reads and Omni-C proximity ligation sequencing technology to produce a de novo assembled genome. Our genome assembly, the first for any species in the genus and third in the family, contains 321 scaffolds spanning 0.572 gigabases with a N50 of 14.6 Mb and BUSCO complete score of 99.1%. This genome will represent a valuable resource for research into the ecology, evolution, and genetics of dietary generalism and diet breadth in insect herbivores. 

Abstract Most insect herbivores specialize on a few host plants; however, there are a minority of highly generalized species capable of feeding on hundreds of hosts. Generalism could emerge as a property of the species as a whole, while individuals would still exhibit greater specialization at more specific organizational levels. Yet, we lack studies with generalist insect herbivores directly testing this prediction. Here, we test if the highly generalized fall webworm (Hyphantria cunea) maintains its broad diet through specialization at the population, maternal genotype, or individual level. We reared two populations and multiple matrilines on either a static or rotating diet of four host plants. We found that both populations survived and pupated on all hosts, suggesting population‐level generalization. We found evidence for generalization at the genotype level, as maternal genotypes did not vary in performance rankings across host plants. Finally, we found generalism at the individual level, as individuals reared on a rotating diet had no difference or showed intermediate performance to those reared on static diets. Overall, we found support for the maintenance of generalism across all levels, suggesting that generalist species need not be locally specialized to maintain their extremely broad diet.