Urbanization is a dominant form of land-use change driving species distributions, abundances, and diversity. Previous research has documented the negative impacts of urbanization on the abundance and diversity of many groups of organisms. However, some organisms, such as bees, may benefit from moderate levels of development, depending on how development alters the availability of foraging and nesting resources. To determine how one type of low-intensity human development, suburbanization, affects bee abundance and diversity and the mechanisms involved, we surveyed bees across suburban and natural forests in the Raleigh-Durham area of North Carolina. We sampled for bees using a combination of bee bowls and hand-netting from March through July of 2008 and 2009. We found higher bee abundance in suburban than natural forests, and although observed species richness was greater in suburban than natural forests, there were no significant differences in rarefied richness or evenness estimates in either year. In addition, the effects of suburbanization were similar across bee species of varying ecological and life-history characteristics. At the local scale, bee abundance and species richness were both positively related to the abundance and richness of flowering species within forests, while the proportion of surrounding developed open areas, such as yards and roadsides, was a strong positive predictor of both bee abundance and richness at the landscape scale. These results suggest that open habitats and the availability of floral resources in suburban sites can support abundant and diverse bee communities and underscore the potential for native bee conservation in urban habitats.

Defense against natural enemies constitutes an important driver of herbivore host range evolution in the wild. Populations of the Baltimore checkerspot butterfly, Euphydryas phaeton (Nymphalidae), have recently incorporated an exotic plant, Plantago lanceolata (Plantaginaceae), into their dietary range. To understand the tritrophic consequences of utilizing this exotic host plant, we examined immune performance, chemical defense, and interactions with a natural entomopathogen (Junonia coenia densovirus, Parvoviridae) across wild populations of this specialist herbivore. We measured three immune parameters, sequestration of defensive iridoid glycosides (IGs), and viral infection load in field‐collected caterpillars using either P. lanceolata or a native plant, Chelone glabra (Plantaginaceae). We found that larvae using the exotic plant exhibited reduced immunocompetence, compositional differences in IG sequestration, and higher in situ viral burdens compared to those using the native plant. On both host plants, high IG sequestration was associated with reduced hemocyte concentration in the larval hemolymph, providing the first evidence of incompatibility between sequestered chemical defenses and the immune response (i.e., the “vulnerable host” hypothesis) from a field‐based study. However, despite this negative relationship between IG sequestration and cellular immunity, caterpillars with greater sequestration harbored lower viral loads. While survival of virus‐infected individuals decreased with increasing viral burden, it ultimately did not differ between the exotic and native plants. These results provide evidence that: (1) phytochemical sequestration may contribute to defense against pathogens even when immunity is compromised and (2) herbivore persistence on exotic plant species may be facilitated by sequestration and its role in defense against natural enemies.

Plant interactions with mutualists and antagonists vary remarkably across space, and have played key roles in the ecology and evolution of flowering plants. One dominant form of spatial variation is human modification of the landscape, including urbanization and suburbanization. Our goal was to assess how suburbanization affected plant-animal interactions in Gelsemium sempervirens in the southeastern United States, including interactions with mutualists (pollination) and antagonists (nectar robbing and florivory). Based on differences in plant-animal interactions measured in multiple replicate sites, we then developed predictions for how these differences would affect patterns of natural selection, and we explored the patterns using measurements of floral and defensive traits in the field and in a common garden. We found that Gelsemium growing in suburban sites experienced more robbing and florivory as well as more heterospecific but not conspecific pollen transfer. Floral traits, particularly corolla length and width, influenced the susceptibility of plants to particular interactors. Observational data of floral traits measured in the field and in a common garden provided some supporting but also some conflicting evidence for the hypothesis that floral traits evolved in response to differences in species interactions in suburban vs. wild sites. However, the degree to which plants can respond to any one interactor may be constrained by correlations among floral morphological traits. Taken together, consideration of the broader geographic context in which organisms interact, in both suburban and wild areas, is fundamental to our understanding of the forces that shape contemporary plant-animal interactions and selection pressures in native species.

Habitat loss and degradation due to agricultural intensification and urbanization are key threats facing wild pollinators, especially bees. However, data on the distribution and abundance of most of the world's 20,000+ bee species is lacking, making it difficult to assess the effects of anthropogenic disturbance through time. Moreover, there are geographic biases in the study of bees creating gaps in our understanding of species distributions and regional patterns of diversity. Research efforts are often focused around cities or field stations associated with universities and other research institutions. In this perspectives paper, we provide examples of geographic bias in knowledge regarding bee species distributions using recently collected data from Michigan and Colorado, USA-two states with published species checklists. We illustrate how a limited sampling effort can advance knowledge about bee species distributions, yielding species occurrence records at local and regional scales. Given the implications of geographic biases, we recommend future research efforts focus on poorly sampled geographic regions, especially those affected by anthropogenic disturbance, in order to expand our understanding of human impacts on wild bee species. Sampling across a broader geographic area will provide critical information for taxonomy and predictive models of bee species distributions and diversity. We encourage researchers to plan future studies with consideration of strategies to avoid oversampling local bee populations, the taxonomic expertise required to identify specimens, and resources necessary to voucher specimens.

These results suggest that florivory can have positive indirect effects on estimated male plant reproduction through changes in different pollinators' behavior at flowers, but the effects of floral damage vary with male vs. female function. These results underscore the importance of other species' interactions at flowers in driving pollinator behavior and pollen transfer dynamics.

Some herbivorous insects sequester chemicals from their host plants, which can serve as a defense against predators. However, sequestration can also be costly, impacting immunological responses important for other types of natural enemies, such as parasites and pathogens. These costs could also vary across herbivorous insect development, as both immune function and sequestration abilities change, although few studies have assessed variation in the cost of sequestration across life stages. The buckeye, Junonia coenia (Nymphalidae), is a specialist butterfly that sequesters iridoid glycosides from its host plants, including the introduced weed, Plantago lanceolata (Plantaginaceae).To determine the immunological costs of sequestration and how the immune response varies with host plant and across development, we reared caterpillars on a native host plant, Mimulus guttatus (Phrymaceae), which does not contain iridoid glycosides, and on P. lanceolata, which does. We assayed immune function across 3rd, 4th, and 5th instar caterpillars, estimating both hemocyte density and the ability of hemocytes to encapsulate foreign bodies by challenging the immune system with nylon filaments. For caterpillars reared on P. lanceolata, we then explored the relationships between iridoid glycoside sequestration and immune function across instars. We found that while hemocyte density tended to increase with instar regardless of host plant, caterpillars reared on P. lanceolata had lower encapsulation ability, and encapsulation decreased with increasing sequestration of iridoid glycosides, though patterns varied between instars and experimental periods. Interestingly, immune challenged caterpillars sequestered more iridoid glycosides than unchallenged caterpillars, suggesting that caterpillars responded to immune challenge by sequestering or retaining more iridoids, even though that may decrease their ability to encapsulate. These results suggest that sequestration can have important consequences for immune function across caterpillar development, and that the incorporation of novel hosts may affect defense against natural enemies.

Over a third of the world's crops require insect pollination, and reliance on pollination services for food continues to rise as human populations increase. Furthermore, as interest in urban agriculture has grown, so has a need for studies of urban pollinator ecology and pollination. Analyzing pollinator assemblages along a rural-urban gradient provides powerful mechanistic insight into how urbanization impacts pollinators. Yet, studies examining pollinators along urban-rural gradients are limited and results vary. Since pollinators vary tremendously in life history characteristics and respond to urbanization differently, studies from different regions would improve our understanding of pollinator response to urbanization. This study documents different bee assemblages along a high-plains semi-arid urban-rural gradient in Denver, Colorado, USA. Percent impervious surface was used to define the extent of urbanization at 12 sites and local and landscape characteristics were estimated using field assessments and geospatial analysis. Wild bees were collected and the relationships between urbanization and bee communities were explored using linear modeling. Overall, bee abundance and diversity decreased with increasing urbanization, suggesting that urban areas negatively impact bee communities. However, all bee guilds responded positively to local floral richness and negatively to the degree of landscape urbanization, suggesting that different types of bees responded similarly to urbanization. These findings suggest that providing a greater diversity of floral resources is key to mitigating the negative impacts of urbanization on pollinator communities.

Incorporation of exotic plants into the diets of native herbivores is a common phenomenon, influencing interactions with natural enemies and providing insight into the tritrophic costs and benefits of dietary expansion. We evaluated how use of an exotic plant, Plantago lanceolata, impacted immune performance, development and susceptibility to pathogen infection in the neotropical herbivore Anartia jatrophae (Lepidoptera: Nymphalidae). Caterpillars were reared on P. lanceolata or a native plant, Bacopa monnieri, and experimentally infected with a pathogenic virus, Junonia coenia densovirus. We found that virus-challenged herbivores exhibited higher survival rates and lower viral burdens when reared on P. lanceolata compared to B. monnieri, though immune performance and development time were largely similar on the two plants. These findings reveal that use of an exotic plant can impact the vulnerability of a native herbivore to pathogen infection, suggesting diet-mediated protection against disease as a potential mechanism facilitating the incorporation of novel resources.