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Abstract Understanding how flying insects manage heat exchange is critical for predicting their survival in dynamic thermal environments. To fly, insects propel air downwards to offset body weight, inducing airflow over their bodies. Remarkably, the potential cooling effect of this self-generated airflow is largely unstudied. We measured induced airflow and wingbeat kinematics for hovering bumble bees (Bombus impatiens) across a range of body sizes and then measured the cooling effect of airflows of the same magnitude in a vertical wind tunnel. We combined these data in heat balance models to predict transient and equilibrium body temperatures of hovering bumble bees with and without self-generated wind. Measured self-induced airflow was substantial (up to 1 m s−1) and varied with body size and wingbeat kinematics, contributing significantly to thermal stability. Without this self-induced airflow, simulated bees of all sizes rapidly overheated across a range of environmental conditions, highlighting the importance of this overlooked heat-loss mechanism in the heat budget of flying insects. Our findings suggest that shifts in wingbeat kinematics required for altered force production not only affect energetics and, therefore, heat production, but also alter the induced airflow and associated convective heat loss. 

Abstract Winter survival in dormant animals depends on conserving finite energy reserves, yet winter temperatures fluctuate around shifting means. In ectotherms, metabolic rate increases exponentially with temperature, so thermal variability is expected to accelerate energy loss, with important consequences for overwinter survival and population persistence under climate change. However, it remains unclear whether dormant ectotherms can compensate physiologically for thermal variability. We overwinteredBombus impatiensqueens under constant (2, 3, 4°C) or variable (2 ± 6°C or 4 ± 6°C) regimes for six weeks, then measured metabolic rates across a range of temperatures. The temperature dependence of metabolic rate shifted in response to thermal experience, but the direction of compensation depended on mean temperature: variability centered on 2°C elevated metabolic rate and increased thermal sensitivity relative to all other conditions, whereas variability centered on 4°C reduced metabolic rate and dampened thermal sensitivity relative to constant 4°C. We used these metabolic responses to simulate rates of lipid depletion and found that survival trajectories echoed physiological shifts: experiencing variability around 2°C would reduce subsequent survival time, whereas experiencing variability around 4°C would preserve subsequent survival even under variable future conditions. Thus, identical thermal variance produced opposite energetic outcomes depending on the mean temperature around which fluctuations occurred. Integrating both temperature means and variability is, therefore, essential for predicting overwintering survival in a changing world. 

Abstract Diapause initiation is determined by photoperiod and temperature in many insect species. In the solitary cavity-nesting bee Megachile rotundata (Fabricius) (Hymenoptera: Megachilidae), which undergoes facultative diapause as a prepupa, photoperiod is an important cue for diapause induction. However, it is unknown if the mother or offspring makes the decision to induce diapause or when this decision is made. Our goal was to answer these questions by manipulating photoperiod during different stages of development in M. rotundata. We subjected mothers to 3 different photoperiods as pupae and released them into the field to build nests and lay eggs when those same photoperiods occurred naturally. Offspring were collected and subjected to the same photoperiods as the mothers. We examined the effects of photoperiod on offspring diapause and the number of nests and brood cells created during each photoperiod. Our findings indicate that the photosensitive period occurs in the field, suggesting that the mother determines diapause during nest construction. We also found that reproductive output is the highest during the shortening photoperiods associated with midsummer. This study furthers our understanding of how diapause functions in Megachile rotundata and could be used to advance commercial management practices. 

ABSTRACT <p>Social bees have been extensively studied for their gut microbial functions, but the significance of the gut microbiota in solitary bees remains less explored. Solitary bee,<italic>Megachile rotundata</italic>females provision their offspring with pollen from various plant species, harboring a diverse microbial community that colonizes larvae guts. The<italic>Apilactobacillus</italic>is the most abundant microbe, but evidence concerning the effects of<italic>Apilactobacillus</italic>and other provision microbes on growth and survival are lacking. We hypothesized that the presence of<italic>Apilactobacillus</italic>in abundance would enhance larval and prepupal development, weight, and survival, while the absence of intact microbial communities was expected to have a negative impact on bee fitness. We reared larvae on pollen provisions with naturally collected microbial communities (Natural pollen) or devoid of microbial communities (Sterile pollen). We also assessed the impact of introducing<italic>Apilactobacillus micheneri</italic>by adding it to both types of pollen provisions. Feeding larvae with sterile pollen +<italic>A. micheneri</italic>led to the highest mortality rate, followed by natural pollen +<italic>A. micheneri</italic>, and sterile pollen. Larval development was significantly delayed in groups fed with sterile pollen. Interestingly, larval and prepupal weights did not significantly differ across treatments compared to natural pollen-fed larvae. 16S rRNA gene sequencing found a dominance of<italic>Sodalis</italic>, when<italic>A. micheneri</italic>was introduced to natural pollen. The presence of<italic>Sodalis</italic>with abundant<italic>A. michene</italic>ri suggests potential crosstalk between both, shaping bee nutrition and health. Hence, this study highlights that the reliance on nonhost-specific environmental bacteria may not impact fitness of<italic>M. rotundata</italic>.</p><sec><title>IMPORTANCEThis study investigates the impact of environmentally acquired gut microbes of solitary bee fitness with insights into the microbial ecology of bee and their health. While the symbiotic microbiome is well-studied in social bees, the role of environmental acquired microbiota in solitary bees remains unclear. Assessing this relationship in a solitary pollinator, the leaf-cutting bee,Megachile rotundata, we discovered that this bee species does not depend on the diverse environmental bacteria found in pollen for either its larval growth or survival. Surprisingly, high concentrations of the most abundant pollen bacteria, Apilactobacillus micheneridid not consistently benefit bee fitness, but caused larval mortality. Our findings also suggest an interaction betweenApilactobacillusand theSodalisand perhaps their role in bee nutrition. Hence, this study provides significant insights that contribute to understanding the fitness, conservation, and pollination ecology of other solitary bee species in the future. 

Abstract The mechanisms that underlie senescence are not well understood in insects. Telomeres are conserved repetitive sequences at chromosome ends that protect DNA during replication. In many vertebrates, telomeres shorten during cell division and in response to stress and are often used as a cellular marker of senescence. However, little is known about telomere dynamics across the lifespan in invertebrates. We measured telomere length in larvae, prepupae, pupae, and adults of two species of solitary bees,Osmia lignariaandMegachile rotundata. Contrary to our predictions, telomere length was longer in later developmental stages in bothO. lignariaandM. rotundata.Longer telomeres occurred after emergence from diapause, which is a physiological state with increased tolerance to stress. InO. lignaria, telomeres were longer in adults when they emerged following diapause. InM. rotundata, telomeres were longer in the pupal stage and subsequent adult stage, which occurs after prepupal diapause. In both species, telomere length did not change during the 8 months of diapause. Telomere length did not differ by mass similarly across species or sex. We also did not see a difference in telomere length after adultO. lignariawere exposed to a nutritional stress, nor did length change during their adult lifespan. Taken together, these results suggest that telomere dynamics in solitary bees differ from what is commonly reported in vertebrates and suggest that insect diapause may influence telomere dynamics. 

Despite repeated calls for ‘adaptive monitoring’, monitoring programs typically rely on fixed protocols that fail to capture the complex and dynamic natural world. New technologies offer this long sought flexibility, yet paradoxically risk our ability to detect trends by generating fragmented, high frequency data untethered to broader monitoring objectives. Here, we introduce ROAM (Routine-Opportunistic Adaptive Monitoring)--a hybrid framework that pairs goal-oriented baseline sampling with the ability to capture critical, transient events and experiment with optimized sampling protocols. We demonstrate ROAM with case studies of spring phenology shifts, biogeochemical pulses, wildlife demography and early warning detection. Needed developments include: 1) infrastructure for real-time communication and rapid sensor deployment, 2) integrated statistical methods for event detection, sampling optimization, and, importantly, merging high-frequency bursts with long-term collection, and 3) equitable technology transfer, training and funding models. This type of monitoring could finally deliver the adaptive, integrated systems both science and policy demand. 

The timing of metamorphosis in insects determines adult body size and influences aspects of fitness including flight performance and fecundity. The regulation of metamorphosis has been well studied in model insects but determining the cue that initiates the physiological shift toward metamorphosis in other insects has been challenging. In most insects, the critical weight is a cue to initiate metamorphosis. Our goal was to determine the cue for metamorphosis in the solitary beeMegachile rotundataand to characterize the physiological mechanisms initiated by this cue. Larval bees were fed ad libitum (also termed “fed”) or had all food removed (also termed “starved”). We measured the time to initiate metamorphosis, juvenile hormone (JH) titers, and the abundance of transcripts involved in the endocrine response to metamorphosis. We experimentally manipulated JH by topically applying precocene, which interrupts JH production. We found thatM. rotundatadoes not have a critical weight and that starvation through the removal of food triggered the initiation of metamorphosis. Food removal was associated with low JH titers, and the application of precocene mimicked the response to food absence. Food removal decreased transcripts associated with JH production, and increased transcripts involved in ecdysone synthesis and insulin/TOR signaling. Food absence is an ecologically relevant cue for aM. rotundatalarva, which is provisioned a finite amount of food and is unable to forage for additional food. Despite having food removal as a cue for metamorphosis, the physiological mechanisms associated with metamorphosis are similar to those found in other insects. 

Many organisms cope with highly variable environmental temperatures by differentiating body temperature from that of the environment through thermoregulation. Heterotherms can both endogenously maintain body temperature with metabolic heat and behaviourally thermoregulate by selecting suitable microclimates. Expending excess energy to maintain stable high body temperatures may be prioritized during certain times of the year, or for certain activities (e.g. reproduction, escape from predation). Alternatively, behavioural thermoregulation may take precedence when energy savings are critical. The degree to which heterotherms rely on these different strategies has rarely been studied. To address this gap, we measured body temperature and selected temperatures on a thermal gradient for heterothermic bumble bee queens (Bombus huntii) at two life stages: during spring, when ovary development prior to colony establishment is critical, and in autumn, when they build energy stores for overwintering. Not only did spring queens have a narrower range of body temperatures than autumn queens, but they maintained higher body temperatures at cooler gradient temperatures. These results suggest that thermoregulatory strategy varies seasonally to sustain key activities but is context dependent: when ambient temperatures are cool, metabolic heat production is relied upon if reproductive pressure is high and reduced if accumulating energy reserves is critical.