Uncertainty remains regarding the role of anthropogenic climate change in declining insect populations, partly because our understanding of biotic response to climate is often complicated by habitat loss and degradation among other compounding stressors. We addressed this challenge by integrating expert and community scientist datasets that include decades of monitoring across more than 70 locations spanning the western United States. We found a 1.6% annual reduction in the number of individual butterflies observed over the past four decades, associated in particular with warming during fall months. The pervasive declines that we report advance our understanding of climate change impacts and suggest that a new approach is needed for butterfly conservation in the region, focused on suites of species with shared habitat or host associations.

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Nutrition structures ecology and evolution across all scales of biological organization. It is well known that nutrition can have direct effects on performance and fitness, but indirect effects on physiological systems that mediate biotic interactions have been studied less frequently. Here, we focus on the interaction between nutrition, performance, and the immune system in a specialist herbivorous insect, Manduca sexta. We used a conceptual framework in nutritional ecology (the geometric framework) to examine how changes in diet quality affect aspects of the immune system used for defense against parasitoids. We raised caterpillars throughout their entire larval development on five different experimental diets that varied in protein and carbohydrate content and measured five aspects of the immune system: encapsulation, phenoloxidase activity, prophenoloxidase activity, total hemolymph protein, and hemocyte density. Overall, different parts of the immune function varied in response to interactions between carbohydrates, protein, and intake, but protein reductions had the largest impactsmostly detrimental. In addition, our data suggest that diet quality mediates the relationship between performance (growth and survival) and immune function, as well as trade-offs among different components of immune function. Our work is the first to examine the interplay between nutrition, performance, and immune function with the geometric framework in a specialist insect herbivore.

Flying animals generate large amounts of heat, which must be dissipated to avoid overheating. In birds, heat dissipation is complicated by feathers, which cover most body surfaces and retard heat loss. To understand how birds manage heat budgets during flight, it is critical to know how heat moves from the skin to the external environment. Hummingbirds are instructive because they fly at speeds from 0 to more than 12 m s−1, during which they transit from radiative to convective heat loss. We used infrared thermography and particle image velocimetry to test the effects of flight speed on heat loss from specific body regions in flying calliope hummingbirds (Selasphorus calliope). We measured heat flux in a carcass with and without plumage to test the effectiveness of the insulation layer. In flying hummingbirds, the highest thermal gradients occurred in key heat dissipation areas (HDAs) around the eyes, axial region and feet. Eye and axial surface temperatures were 8°C or more above air temperature, and remained relatively constant across speeds suggesting physiological regulation of skin surface temperature. During hovering, birds dangled their feet, which enhanced radiative heat loss. In addition, during hovering, near-body induced airflows from the wings were low except around the feet (approx. 2.5 m s−1), which probably enhanced convective heat loss. Axial HDA and maximum surface temperature exhibited a shallow U-shaped pattern across speeds, revealing a localized relationship with power production in flight in the HDA closest to the primary flight muscles. We conclude that hummingbirds actively alter routes of heat dissipation as a function of flight speed.

Insect carnivores frequently use olfactory cues from plants to find prey or hosts. For plants, the benefits of attracting parasitoids have been controversial, partly because parasitoids often do not kill their host insect immediately. Furthermore, most research has focused on the effects of solitary parasitoids on growth and feeding of hosts, even though many parasitoids are gregarious (multiple siblings inhabit the same host). Here, we examine how a gregarious parasitoid, the tachinid fly Drino rhoeo, uses olfactory cues from the host plant Datura wrightii to find the sphingid herbivore Manduca sexta, and how parasitism affects growth and feeding of host larvae. In behavioral trials using a Y-olfactometer, female flies were attracted to olfactory cues emitted by attacked plants and by cues emitted from the frass produced by larval Manduca sexta. M. sexta caterpillars that were parasitized by D. rhoeo grew to lower maximum weights, grew more slowly, and ate less of their host plant. We also present an analytical model to predict how tri-trophic interactions change with varying herbivory levels, parasitization rates and plant sizes. This model predicted that smaller plants gain a relatively greater benefit compared to large plants in attracting D. rhoeo. By assessing the behavior, the effects of host performance, and the variation in ecological parameters of the system, we can better understand the complex interactions between herbivorous insects, the plants they live on and the third trophic level members that attack them.

Nutrition has far‐reaching effects on both the ecology and evolution of species. A substantial body of work has examined the role of host plant quality on insect herbivores, with a particular focus on specialist–generalist dynamics, the interaction of growth and other physiological attributes on fitness and tritrophic effects. Measures of plant quality usually involve one or two axes of nutritional space: typically secondary metabolites or elemental proxies (N and C) of protein and carbohydrates, respectively.Here, we describe the nutrient space of seven host plants of the specialist insect herbivore, Manduca sexta, using an approach that measures physiologically relevant sources of nutrition, soluble protein and digestible carbohydrates. We show that plant species differ markedly in their nutrient content, offering developing insect herbivores a range of available nutrient spaces that also depend on the age of the leaves being consumed.The majority of host‐plant species produce diets that are suboptimal to the herbivore, likely resulting in varying levels of compensatory feeding for M. sexta to reach target levels of protein to ensure successful growth and development. Low‐quality diets can also impact immune function leading to complex patterns of optimization of plant resources that maximizes both growth and the ability to defend from parasitoids and pathogens. This study is the first to quantify the nutrient space of a suite of host plants used by an insect herbivore using physiologically relevant measures of nutrition.

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