Dietary generalist herbivore shows individual-level generalism

As diet specificity has the capacity to facilitate divergence, the high degree of specialization that is typically associated with insect herbivores is considered an important facet in the maintenance of Earth’s biodiversity. Thus, it is no surprise that diet specialization is represented in >90% of insect herbivores. Yet, some extreme dietary generalist species have retained the ability to consume hundreds of host species. These generalist species also tend to be widespread and thus encounter multiple hosts across their range. In such cases, it remains unknown if these dietary generalists are truly generalists at the individual level or instead a composite of locally specialized populations or cryptic specialized species. Here, utilize two diverging biotypes with varying diet-breadths of the extreme generalist fall webworm (Hyphantria cunea, Erebidae) we test for potential physiological constraints that would reinforce specialization at the individual or species level. We measured the performance of each biotype reared on either a diet consisting of one-of-four hosts of variable quality or a rotating diet of all four where we switched host species every 6-days. Our findings show differential performance by host and these differences are distinct between, but not within, biotype. Performance on the rotating diet was intermediate to that of the other hosts. Additionally, genotype influenced performance across matrilines, but not host-associated performance. Together these findings suggest that genotype and environment are playing different roles in moderating diet and that this dietary generalist is not a composite of highly specialized populations but rather true generalists at the individual level.