Respiration and metabolism of the resting European paper wasp (Polistes dominulus)

Ontogenetic variation in metabolic rate-temperature relationships during larval development

Predictive models of ectotherm responses to environmental change often rely on thermal performance data from the literature. For insects, the majority of these data focus on two traits, development rate and thermal tolerance limits. Data are also often limited to the adult stage. Consequently, predictions based on these data generally ignore other measures of thermal performance and do not account for the role of ontogenetic variation in thermal physiology across the complex insect life cycle. Theoretical syntheses for predicting metabolic rate also make similar assumptions despite the strong influence of body size as well as temperature on metabolic rate. The aim of this study was to understand the influence of ontogenetic variation on ectotherm physiology and its potential impact on predictive modeling. To do this, we examined metabolic rate-temperature (MR-T) relationships across the larval stage in a laboratory strain of the spongy moth (Lymantria dispar dispar). Routine metabolic rates (RMRs) of larvae were assayed at eight temperatures across the first five instars of the larval stage. After accounting for differences in body mass, larval instars showed significant variation in MR-T. Both the temperature sensitivity and allometry of RMR increased and peaked during the third instar, then declined in the fourth and fifth instar. Generally, these results show that insect thermal physiology does not remain static during larval ontogeny and suggest that ontogenetic variation should be an important consideration when modeling thermal performance.

The costs of overwintering in paper wasps (Polistes dominula and Polistes gallicus): the use of energy stores

Overwintering insects are facing energetic challenges because of food shortage, low temperature, and desiccation stress. Paper wasps of the genus Polistes overwinter as mated adults (gynes) in hibernacula protecting them from predation, snow, and rain but barely from low environmental temperature. In different climates, they face differing overwintering temperature regimes, and therefore they may differ in their energy use. We investigated how much of energy resources built up until autumn is used during diapause dormancy in natural hibernacula by measuring lipid, glycogen, and free carbohydrate content in autumn and early spring in Polistes dominula from temperate European (Austrian) and warm Mediterranean (Italian) climate and Polistes gallicus from Mediterranean climate. Winter energy consumption amounted to ~ 339 and ~ 310 J per wasp in the Austrian and Italian Polistes dominula populations. The smaller Italian Polistes gallicus consumed ~ 247 J. This amounts to 2.62, 2.35, and 1.79 J per day. Of this, the energy demand was mainly fuelled by lipids (84%, 93%, and 90%, respectively), but glycogen stores contributed also considerably (16%, 6%, and 9%). Free carbohydrates decreased only by 0.7%, 1%, and 0.8%. While fat stores seem still sufficient in spring, the wasps depleted most of their carbohydrates. The energy reserves of 396, 400, and 147 J per wasp remaining in spring in the three populations seem sufficient to fuel rest or simple brood care activities for a whole summer but restrict foraging flights to a few hours (~ 3.5-6 h). Results suggest that energy supply might become challenging in expected future climate scenarios.

Relationship between Nest and Body Temperature and Microclimate in the Paper Wasp Polistes dominula

The paper wasp Polistes dominula is a thermophilic species originating from the Mediterranean climate, but is now widely spread in Europe. They live in quite differing habitats; and as synanthropic species, they have been established in human settlement areas. They build a single small comb at protected places with a favorable microclimate. We measured the temperature of the wasps, the nests and their environment at typical nesting sides in Austria (Europe) in the temperate climate, in order to reveal relationships between nest and body temperature and the habitats' microclimate. The temperatures of the comb and of the wasps' body were in a wide range (~20-37 °C) above the ambient air temperature at the nest. This is an advantage as higher temperatures accelerate the development speed of the brood. However, the mean comb temperature did not exceed approximately 38.6 °C. This was managed by cooling efforts of the adult wasps. The ambient air temperature near the nest (~1-2 cm) was always clearly elevated above the ambient air temperature at a local standard weather station in the habitat. A comparison with climate-model-generated macroclimate data revealed the necessity of measuring microclimate data for a reliable description of the insects' thermal environment.

The Impact of Climate on the Energetics of Overwintering Paper Wasp Gynes (Polistes dominula and Polistes gallicus)

Gynes of paper wasps (Polistes sp.) spend the cold season in sheltered hibernacles. These hibernacles protect against predators and adverse weather conditions but offer only limited protection against low temperatures. During overwintering diapause, wasps live on the energy they store. We investigated the hibernacles' microclimate conditions of species from the Mediterranean (Italy, P. dominula, P. gallicus) and temperate (Austria, P. dominula) climates in order to describe the environmental conditions and calculate the energetic demand of overwintering according to standard metabolic rate functions. The temperatures at the hibernacles differed significantly between the Mediterranean and temperate habitats (average in Austria: 3.2 ± 5.71 °C, in Italy: 8.5 ± 5.29 °C). In both habitats, the hibernacle temperatures showed variance, but the mean hibernacle temperature corresponded closely to the meteorological climate data. Cumulative mass-specific energetic costs over the studied period were the lowest for the temperate P. dominula population compared with both Mediterranean species. The lower costs of the temperate species were a result of the lower hibernacle temperature and acclimation to lower environmental temperatures. Model calculations with an increased mean temperature of up to 3 °C due to climate change indicate a dramatic increase of up to 40% in additional costs.

Nesting Biology of the Potter Wasp Ancistrocerus flavomarginatus (Hymenoptera, Vespidae, Eumeninae) Revealed by Trap-Nest Experiments in Southern Brazil

This paper provides the first description of the nesting biology of Ancistrocerus flavomarginatus (Brèthes) (Hymenoptera, Vespidae, Eumeninae), the only species of the genus found in Brazil. Our trap-nest experiments were conducted in two Mixed Ombrophilous Forest fragments and two adjacent matrices in Guarapuava (Paraná state, Brazil) from August 2017 to July 2018. In each area, we set 192 trap nests divided into six groups of 32 units, totalling 768 trap nests. We obtained a total of 47 nests of A. flavomarginatus, the vast majority of them (43, 91.5%) founded in the forest fragments. Most nests were built in wooden traps with a bore diameter of either 5 or 7 mm (19 nests in each type, 80.8%). Nests comprised 1-12 subcylindrical brood cells arranged linearly and separated from one another by transverse partitions of soil mastic. Larvae consumed 6-10 lepidopteran caterpillars before spinning the cocoon. Ancistrocerus flavomarginatus produced up to 6 annual generations (multivoltinism) and its immature forms were parasitized by chrysidid and ichneumonid wasps. The calculated sex ratio (1.78:1) was statistically biased towards males, but since they (21.3 ± 2.0 mg) were significantly lighter than females (50.9 ± 4.0 mg), the resulting investment ratio (1.34:1) was female biased. Males emerged from more external cells and developed significantly faster (27.2 ± 0.46 days) than females (30.1 ± 0.66 days), hence a case of protandry. We demonstrated that A. flavomarginatus is largely dependent on the Atlantic Rainforest and thus that deforestation poses a critical threat to this important species.

Energetics of Paper Wasps (Polistes sp.) from Differing Climates during the Breeding Season

Paper wasps are widely distributed in Europe. They live in the warm Mediterranean, and in the harsh Alpine climate. Some species are very careful in their choice of nesting sites to ensure a proper development of the brood. We investigated microclimate conditions at the nests of three species (P. dominula, P. gallicus, P. biglumis) from differing climates, in order to characterize environmental conditions and conduct energetic calculations for an entire breeding season. The mean ambient nest temperature differed significantly in the Mediterranean, temperate, and Alpine habitats, but in all habitats it was about 2 to 3 °C above the standard meteorological data. The energetic calculations of adult wasps' standard and active metabolic rate, based on respiratory measurements, differed significantly, depending on the measured ambient temperatures or the wasps' body temperatures. P. gallicus from the warm Mediterranean climate exhibited the highest energetic costs, whereas P. biglumis from the harsh Alpine climate had the lowest costs. Energetic costs of P. dominula from the temperate climate were somewhat lower than those in the Mediterranean species, but clearly higher than those in the Alpine species. Temperature increase due to climate change may have a severe impact on the wasps' survival as energetic costs increase.

Relation between activity, endothermic performance and respiratory metabolism in two paper wasps: Polistes dominula and Polistes gallicus

Climate change is expected to produce shifts in species distributions as well as behavioural and physiological adaptations to find suitable conditions or to cope with the altered environment. The paper wasps Polistes dominula and Polistes gallicus are closely related species, native in the European Mediterranean region and North Africa. P. dominula has expanded its range to the relatively cooler climates of Northern and Eastern Europe, but P. gallicus remained in its original distribution area. In order to reveal their metabolic adaptation to the current climate conditions, and the impact on energy demand at future climate conditions, we investigated the respiratory metabolic rate (CO₂ production) of P. dominula from Austria and P. gallicus from Italy. In contrast to the metabolic cold adaptation hypothesis their standard metabolic rate was nearly the same and increased in a typical exponential course with increasing ambient temperature. The metabolic rate of active wasps was higher than the standard metabolic rate and increased with the wasps' activity. There was no obvious difference in the active metabolism between the two species, with the exception that some P. gallicus individuals showed some extraordinary high values. A simultaneous measurement of metabolic rate and body temperature revealed that increased CO₂ production was accompanied by endothermic activity. The two investigated populations of paper wasps are quite similar in their metabolic response to temperature, although they live in different climate regions. The spread of P. dominula into cooler regions did not have significant influence on their active and standard metabolic rate.

The Respiratory Metabolism of Polistes biglumis, a Paper Wasp from Mountainous Regions

European Polistine wasps inhabit mainly temperate and warm climate regions. However, the paper wasp Polistes biglumis represents an exception; it resides in mountainous areas, e.g., in the Alps and in the Apennines. In these habitats, the wasps are exposed to a broad temperature range during their lifetime. We investigated whether they developed adaptations in their metabolism to their special climate conditions by measuring their CO₂ production. The standard or resting metabolic rate and the metabolism of active wasps was measured in the temperature range which they are exposed to in their habitat in summer. The standard metabolic rate increased in a typical exponential progression with ambient temperature, like in other wasps. The active metabolism also increased with temperature, but not in a simple exponential course. Some exceptionally high values were presumed to originate from endothermy. The simultaneous measurement of body temperature and metabolic rate revealed a strong correlation between these two parameters. The comparison of the standard metabolic rate of Polistes biglumis with that of Polistes dominula revealed a significantly lower metabolism of the alpine wasps. This energy saving metabolic strategy could be an adaptation to the harsh climate conditions, which restricts foraging flights and energy recruitment.

Thermoregulatory syndromes of two sympatric dung beetles with low energy costs

In heterotherm insects, endothermy implies a high energy cost due to the generation and regulation of body temperature during different activities such as flight, food location, fighting and even walking. We studied the thermoregulation process and the cost of the thermoregulation strategies in two sympatric dung beetles, Sulcophanaeus batesi and S. imperator under heat and cold stress conditions. We used a set of physiological variables to exemplify the capacity of thermolimit respirometry combined with infrared thermography to derive relevant variables capable of describing different thermoregulation syndromes. Habitat use and thermal niche differed notably between S. batesi and S. imperator, reflecting their contrasted thermal requirements. In S. imperator, thermal specialization for high temperatures was observed, being active mainly during the warmer period of the day. On the other hand, thermal adaptation in S. batesi allows its preference for cold exhibiting a morning activity periods, avoiding higher temperatures. The thermophilic strategy used by Sulcophanaeus imperator minimized the energy expenditure produced during the cooling of the body by respiration without thereby endangering higher thermal limits. In this case, S. batesi, the species with a preference for the coldest environments, presented the lowest thermal limits, although the energy cost needed to stay active during cooling was significantly lower than that in S. imperator. Sulcophanaeus imperator and S. batesi showed evident 'economizing' strategies associated with hot and cold environmental conditions, respectively. In contrast, if both species experience a deviation from their thermal optimum, a decrement in their performance could be produced.

Metabolic rate scaling, ventilation patterns and respiratory water loss in red wood ants: activity drives ventilation changes, metabolic rate drives water loss

Metabolic rate and its relationship with body size is a fundamental determinant of many life history traits and potentially of organismal fitness. Alongside various environmental and physiological factors, the metabolic rate of insects is linked to distinct ventilation patterns. Despite significant attention, however, the precise role of these ventilation patterns remains uncertain. Here we determine the allometric scaling of metabolic rate and respiratory water loss in the red wood ant, as well as assessing the effect of movement upon metabolic rate and ventilation pattern. Metabolic rate and respiratory water loss are both negatively allometric. We observed both continuous and cyclic ventilation associated with relatively higher and lower metabolic rates, respectively. In wood ants, however, movement not metabolic rate is the primary determinant of which ventilation pattern is performed. Conversely, metabolic rate not ventilation pattern is the primary determinant of respiratory water loss. Our statistical models produced a range of relatively shallow intraspecific scaling exponents between 0.40 and 0.59, emphasising the dependency upon model structure. Previous investigations have revealed substantial variation in morphological allometry among wood ant workers from different nests within a population. Metabolic rate scaling does not exhibit the same variability, suggesting that these two forms of scaling respond to environmental factors in different ways.

Comparison of thermal traits of Polistes dominula and Polistes gallicus, two European paper wasps with strongly differing distribution ranges

The two paper wasps, Polistes dominula and Polistes gallicus, are related species with strongly differing distribution ranges. We investigated thermal tolerance traits (critical thermal limits and metabolic response to temperature) to gain knowledge about physiological adaptations to their local climate conditions and to get evidence for the reasons of P. dominula’s successful dispersion. Body and ambient temperature measurements at the nests revealed behavioural adaptations to microclimate. The species differed clearly in critical thermal minimum (P. dominula −1.4 °C, P. gallicus −0.4 °C), but not significantly in critical thermal maximum of activity (P. dominula 47.1 °C, P. gallicus 47.6 °C). The metabolic response did not reveal clear adaptations to climate conditions. At low and high temperatures, the metabolic rate of P. dominula was higher, and at intermediate temperatures, we determined higher values in P. gallicus. However, the species exhibited remarkably differing thermoregulatory behaviour at the nest. On average, P. gallicus tolerated a thoracic temperature up to ~41 °C, whereas P. dominula already tried at ~37 °C to keep the thorax below ambient temperature. We suggest this to be an adaptation to the higher mean ambient temperature we measured at the nest during a breeding season. Although we determined for P. dominula a 0.5 °C larger thermal tolerance range, we do not presume this parameter to be solely responsible for the successful distribution of P. dominula. Additional factors, such as the thermal tolerance of the queens could limit the overwintering success of P. gallicus in a harsher climate.