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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 Multispecies mutualistic interactions are ubiquitous and essential in nature, yet they face several threats, many of which have been exacerbated in the Anthropocene era. Understanding the factors that drive the stability and persistence of mutualism has become increasingly important in light of global change. Although dispersal is widely recognized as a crucial spatially explicit process in maintaining biodiversity and community structure, knowledge about how the dispersal of mutualists contributes to the persistence of mutualistic systems remains limited. In this study, we used a synthetic mutualism formed by genetically modified budding yeast to investigate the effect of dispersal on the persistence and stability of mutualisms under exploitation. We found that dispersal increased the persistence of exploited mutualisms by 80% compared to the isolated systems. Furthermore, our results showed that dispersal increased local diversity, decreased beta diversity among local communities, and stabilized community structure at the regional scale. Our results indicate that dispersal can allow mutualisms to persist in meta-communities by reintroducing species that are locally competitively excluded by exploiters. With limited dispersal, e.g. due to increased fragmentation of meta-communities, mutualisms might be more prone to breakdown. Taken together, our results highlight the critical role of dispersal in facilitating the persistence of mutualism. 

Abstract Insect colouration mediated by melanization can assist in dealing with environmental temperatures. However, melanin synthesis can be costly and depends on the ability of insects to acquire enough energy and nutrients from their diets. Due to the increased plant C:N ratio associated with elevated CO₂concentrations, insect herbivores' melanization could be limited by the amount of nitrogen they acquire from their host plants.To investigate how diet C:N impacts the potential colour response to temperature, we usedManduca sextacaterpillars reared at different combinations of temperatures and diet C:N ratios, and measured pupal mass and development time (performance metrics) and colour morphology.The high‐temperature treatment (27°C) had a positive impact on larval performance, whereas a nitrogen‐poor diet was related to lower performance. Using a fitness metric that considers both pupal mass and development time, we found a positive effect of both high temperature and nitrogen‐rich diet treatments on larval fitness.We found that diet and temperature affected the colouration of larvae, in which larvae reared at the low‐temperature treatment (18°C) and fed a nitrogen‐rich diet were darker than their counterparts.Our results provide experimental evidence of the impact of diet on melanization and suggest that CO₂‐related changes in plant quality could be associated with changes in insect herbivore performance and colouration.