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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 Parents can provide care to their offspring to increase their offspring's chance of survival. There are various types of parental care across insect taxa, one of which is maternal investment. Lipids, the most energy‐dense of macronutrients, are considered a good estimate of maternal investment in insects. However, it is not clear how different environments, such as host plants, can impact provisioning, especially for dietary generalists that feed on an array of plant species with varying quality. Using an extreme dietary generalist, fall webworm (FW,Hyphantria cunea), we investigated if females provision different amounts of lipids into their eggs depending on the diet they fed upon as larvae. We measured the lipid content of FW egg clusters from parents reared on seven host plant species of varying quality. We found that parental host plants influenced egg provisioning, such that provisioning depends on host plant but also increases most for parents reared on low‐quality diets. Additionally, we found that female parents with heavier pupal mass produced egg clusters with greater lipids per egg. Our results provide evidence that egg provisioning can depend on the parental environment and suggest that the use of low‐quality host plants by generalist herbivores may be partially overcome via maternal investment. 

Abstract Why and how herbivorous insects choose to feed on some plant species and not others can be influenced by many factors; however, it is not always clear why herbivorous insects will choose to lay their eggs on some plants over others. The Hopkins’ host selection principle (hereafter HHSP) hypothesizes that female insects prefer to lay eggs on host plants upon which they fed as larvae, but there are studies that both support and refute the hypothesis. Here, we test HHSP in a dietary generalist moth, fall webworm (Hyphantria cunea, hereafter FW). Previously, local host plant abundance has been the only factor found to determine FW host plant use; whether FW exhibit individual host plant preferences is unknown. We conducted preference tests with females of the two FW morphotypes (red-head and black-head), presenting females with four host plants: their one natal host plant, two other potential host plants, and one non-host plant for that morphotype that is a host plant for the other morphotype. Overwhelmingly, females of both morphotypes oviposited on a non-plant surface in the choice arena and those that did oviposit on a plant did not distinguish between host plants and non-host plants. Of the few FW females that oviposited on a host plant, only red-head females showed preference for their natal hosts. Our results support previous findings that HHSP is not a strong driver of host plant selection, suggesting that female FW are not selective in their choice of host plants, which may facilitate generalism in this species. 

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.