Thoracic Temperature Research Articles

Synchronous Crepuscular Flight of Female Asian Gypsy Moths: Relationships of Light Intensity and Ambient and Body Temperatures

Female gypsy moths (Lymantria dispar) of Asian heritage studied in central Siberia and Germany exhibit a highly synchronous flight at dusk, after light intensity falls to about 2 lux. This critical light intensity sets the timing of flight behaviors independent of ambient temperature. Flight follows several minutes of preflight wing fanning during which females in Germany and those from a laboratory colony (derived from Siberian stock) raised their thoracic temperatures to 32–33°C at ambient temperatures of 19–22°C. Thoracic temperature of females in free flight exceeded the air temperature (19–22°C) by approximately 11–13°C. The duration of wing fanning was strongly dependent on ambient temperature. In Germany, where ambient temperatures at dusk ranged between 21 and 25°C, females wing fanned for only 2.1 ± 0.2 (SE) min; in the much colder temperatures prevalent at dusk in Bellyk, central Siberia (11–13°C), females spent 11.2 ± 0.6 min in preflight wing fanning. The majority (≤80%) of mated and even virgin females initiated flight during the evening of the day they eclosed. However, in Bellyk, a small proportion (12%) of females wing fanned for an extended time but then stopped, whereas others (8%) never wing fanned and, therefore, did not take flight. Females also were capable of flight when disturbed during the daylight hours in Germany where the maximal temperature was high (27–30°C), but not in Siberia, where temperatures peaked at only 17–19°C. However, Siberian females were able to propel themselves off the tree on which they were perched by executing several vigorous wing flicks when approached by the predaceous tettigoniid, Tettigonia caudata.

Proline powers pre-flight warm-up in the african fruit beetle pachnoda sinuata

We investigated thoracic temperatures (Tth) during different activities of the endothermic fruit beetle Pachnoda sinuata and analysed which energy substrates are used for the pre-flight warm-up of its flight muscles. Pachnoda sinuata elevates its Tth prior to take-off either by basking in the sun or by warming endothermically to a narrow range around 34 degreesC. During lift-generating tethered flight at low ambient temperatures (Ta=25 degreesC), Tth of P. sinuata decreases steadily until it reaches 28 degreesC, which is not sufficiently high to sustain flight. Tth remains stable during lift-generating tethered flight at high Ta (31 degreesC). Wingbeat frequency (fw) is dependent on Tth: when Tth declines, fw decreases in a linear manner. The proline concentrations in the haemolymph and flight muscles decrease during warm-up. In contrast, the carbohydrate levels in the haemolymph and flight muscles are not affected by the warm-up process, while the glycogen level of the flight muscles declines significantly during the first 10 s of lift-generating tethered flight. This suggests that the energy for endothermic warm-up is produced solely by the oxidation of proline. Measurements of the respiratory quotient (RQ) confirmed that P. sinuata uses a combination of carbohydrates and proline to power its flight. At rest and during lift-generating tethered flight, the RQ is approximately 0.9. During warm-up, the RQ is significantly lower at 0.82, which is close to the theoretical value of 0.8 for the partial oxidation of proline. The rate of oxygen consumption during endothermic warm-up is 45 % of that during lift-generating tethered flight

Thermoregulatory differences between phenotypes in the speckled wood butterfly: hot perchers and cold patrollers?

Males of the speckled wood butterfly Pararge aegeria L. (Satyrinae), actively search for females ("patrolling") or wait for them at particular places ("perching"). Darker males are more likely to patrol than pale ones, which are mainly territorial perchers. We studied whether this morphological variation relates to thermoregulatory differences. The relationship between thoracic temperature and ambient temperature differed between the colour types under natural conditions: darker males had on average lower body temperatures than paler males. Different activities (e.g. resting, flying) and behavioural strategies (perching or patrolling) were associated with differences in thoracic temperature: patrolling males which mainly engaged in long flights and periods of basking afterwards, had lower thoracic temperatures than perching males which engaged in very short flights, fights and basking. When resting for a while thoracic temperatures did not differ between males practising different strategies. Under laboratory conditions, darker males heated up faster than pale males but there was no difference in the thoracic temperature at which they started to fly. These results indicate that thermal requirements (or general conditions) differ between the behavioural strategies, and that behavioural differences between phenotypes (colour types) relate to differences in thermal ecology. This supports the idea that darker males are better adapted to patrolling. There is no evidence that one mate-locating strategy is always superior to the other, which coincides with the observation that both strategies co-exist. More generally, this study shows that relatively small differences in colour can have a considerable effect on thermoregulation and hence on the behavioural strategies a heliothermic insect will adopt.

Endothermy and floral utilization of Cyclocephala caelestis (Coleoptera: Scarabaeoidea; Melolonthidae): a cloud forest endemic beetle.

Un estudio sobre la ecología de la polinización de Magnolia tamaulipana y su polinízador, Cyclocephala caelestís, fue realizado en la Reserva de la Biósfera El Cielo, Tamaulipas, durante la primavera de 1996. Cyclocephala caelestis visitó las flores de M. tamaulipana con mayor frecuencia después de las 21:00 horas, siendo los machos más abundantes que las hembras. Citamos por primera vez dentro del género, la endotermia y reguladón da la temperatura torácica en C. caelestis. El promedio de la temperatura torácica fue de 26.8°C ± SE = 0.3 con un exceso ds 4.7°C ± SE - 0.3 sobre la temperatura ambiental. Los machos y hembras no se diferenciaron en su temperatura torácica media. En el interior de las flores, los escarabajos regularon su temperatura torácica, independientamente de las temperaturas ambiental y floral, y fueron observados apareándose y alimentándose de los pétalos. La endotermia quiza sea importante para realizar estae actividades de apareamiento y alimentación, las cuales las realizan durante la noche cuando disminuye la temperatura. Se piensa que el tejido de los pétalos contiene aceites etéreos en los que se disuelven ésteres quirales que son responsables del aroma floral y la atracción de las especies de Cyclocephala. Los tejidos de pétaloe y sépalos contierren altas cantidades de carbohidratos y proteínas, sin embargo los pétalos presentan cuatro veces menos fibra, lo que probablemente explique el porque Cyclocephala, los prefiere como alimento.

Thermal Biology and Foraging Responses of Insect Pollinators to the Forest Floor Irradiance Mosaic

This paper examines the responses of the insect pollinators of the summer-flowering, understorey shrub, Lavandula latifolia (Labiatae) to the irradiance mosaic of the forest floor in a southeastern Spanish locality, and assesses the relationship between these responses and interspecific variation in thermal biology. Pollinators differed significantly in the mean irradiance at capture points (MICP), and a large percentage of species (59%) preferentially selected plants in either shaded or sunlit conditions. Taxonomic affiliation (at the order level) and body size explained 78% of interspecific variance in MICP. Dipterans tended to be restricted to situations of relatively low irradiance, whereas hymenopterans foraged over the entire irradiance gradient. MICP was inversely related to body size. Pollinators differed significantly in mean thoracic temperature (T th ), thoracic temperature excess (T exc = T th - T a [air temperature]), and slope of the T th /T a regression (which may be taken as a rough index of thermoregulatory ability). Hymenopterans had higher T th and T exe , and smaller T th /T a slopes, than dipterans. After accounting for this taxonomic effect, T th and T exc , but not T th /T a slope, increased with body size. MICP depended significantly on T exc and, to a lesser degree, on T th , and species characterised by high T exc tended to select low-irradiance conditions. The relationship between MICP and body size was thus mediated by the correlations between the latter variable and thermal biology parameters. In the hot Mediterranean summer, as in other thermally stressing environments, thermal constraints of the kind reported in this study may generate within- and between-habitat variation in the composition and size structure of pollinator assemblages, which may be consequential for plant reproduction.

Thermoregulation of honeybees ( Apis mellifera) foraging in spring and summer at different plants

The body temperature of honeybees ( Apis mellifera carnica Pollm.) was determined by infrared measuring instruments without touching the animals. From spring until summer the insects were observed on 13 different species of plants while foraging nectar and pollen within their natural environment. In this way it was possible for the first time to measure the body surface temperatures of all three parts of the body continuously and often simultaneously without disturbing the animals in their activity. It was remarkable that in spring at an ambient temperature from 12–20 °C on average the thorax was warmer by 6.4 °C and the head by 4.1°C than in summer (ambient temperature: 20–26 °C). The temperatures of all three parts of the body always exceeded ambient temperature. The thorax was the warmest part of the body. Concerning caput and abdomen, which were distinctly cooler, a slight dependence on the ambient temperature could be observed. The temperature of the abdomen, the coolest part of the body, never fell below 20.6 °C. It was obvious that heat was exchanged between the thorax and the two other parts of the body. The average thoracic temperature amounted to 35.7 °C in spring and to 29.3 °C in summer. The mean temperature of the head was 30.9 °C in spring and 26.8 °C in summer, that of the abdomen 25.2 °C and 23.1 °C. The higher body temperatures in spring possibly protect the bees against cooling at the lower ambient temperature.

Effects of Temperature and Thermoregulation on Mycosis byBeauveria bassianain Grasshoppers

Abstract The influence of behavioral thermoregulation by grasshoppers (Melanoplus sanguinipes) on mycosis caused byBeauveria bassianawas investigated in controlled environments. The cardinal temperature forB. bassianaconidial germination and hyphal development was approximately 35°C. A low prevalence of mycosis (≤7%) was observed in inoculated nymphs exposed to a continuous temperature of 35 and 40°C, whereas continuous exposure to 30°C did not have a significant effect on disease development. Daily exposures to 35 and 40°C for 1 and 6 h, respectively, decreased mycosis in nymphs. In both environments, a strong correlation (r ≥ 0.95) was observed between hyphal growth on potato dextrose agar and final mycosis. Although high temperatures delayed conidial germination, only conidia exposed to continuous 35 or to 40°C for more than 8 h exhibited reduced germination after 24 h. The effects of temperature on conidial germination were poorly correlated with disease, and when nymphs were exposed to 35°C for 24 h, less mycosis was observed only in grasshoppers exposed between 1 and 2 days postinoculation. The thoracic temperature of nymphs permitted to bask adjacent to a heat source ranged from 38 to 42°C. In nymphs basking for 1 h per day, 46% less mycosis was observed, decreasing to 98% less disease in nymphs allowed to bask for 6 h or greater per day. On a heat gradient, a higher prevalence ofB. bassiana-infected nymphs selected hotter positions than noninfected nymphs, suggesting a “behavioral fever” response to infection. This study indicates that high temperature and thermoregulation can adversely affectB. bassianamycosis of grasshoppers and may explain the poor efficacy of this entomopathogen observed in some field experiments.

Exercise hyperpnea and hyperthermia in humans.

The problem of the relative hyperpnea occurring at high levels of exercise remains unresolved. This study examined whether the hyperpnea observed in humans during exercise at approximately 70% of maximal work capacity was related to cranial (tympanic) and thoracic (esophageal) temperatures. Six trained male subjects pedaled at approximately 60 revolutions/min on an electrically braked cycle ergometer in a climatic chamber at 25 degrees C and approximately 35% relative humidity in two sessions. The subjects pedaled until exhaustion in two sessions. In one session work rate was increased by 40 W every 2 min and in the other session by 20 W every 2 min. In both exercise sessions, core temperature thresholds for ventilation were evident and subsequently tympanic and esophageal temperatures diverged. This suggested that the hyperpnea in humans observed after approximately 70% of an individual's maximal work rate was determined, in part, by core temperatures and revealed supportive evidence for selective brain cooling in humans.

Neural parameters contributing to temperature compensation in the flight CPG of the locust,Locusta migratoria

Elevated thoracic temperature increases the wingbeat frequency of flying locusts. We investigated the extent to which temperature-induced changes in resting membrane potential and postsynaptic potential amplitude contribute to the effects of increased temperature on the frequency of the central flight rhythm. Flight neurons were hyperpolarized by changing the K+ concentration of the superfusing saline from 10 mM to 2 mM. 5 min of low-K+ superfusion hyperpolarized flight motoneurons from −42.8 mV to −50.1 mV with a concomitant decrease of the frequency of the central flight rhythm from 11.6 Hz to 10.5 Hz. The amplitude of postsynaptic potentials was halved after 10 min of zero Ca2+/high Mg2+ superfusion, but the frequency of the central rhythm did not change significantly. GABAergic inhibitory connections were reduced in amplitude using picrotoxin. This treatment increased the frequency of the central rhythm from 11.6 Hz to 12.9 Hz, and increased the thermosensitivity of the rhythm frequency. We conclude that the excitatory effect of increased temperature on rhythm frequency is not mediated by temperature effects on membrane potential and/or synaptic potential amplitude. We propose that the inhibitory effect of temperature-induced hyperpolarization of the membrane potential compensates for the excitatory effect of temperature on rhythm frequency (e.g. via increased conduction velocity). We further suggest that some measure of temperature compensation is afforded by equal effects on the amplitudes of excitatory and inhibitory postsynaptic potentials, such that the net effect on the level of excitation is zero.

Modulation of honey bee thermoregulation by adrenergic compounds.

The effects of adrenergic compounds on the thermoregulation of resting honey bees were investigated using a non-traumatizing approach. Bees fed ad lib were treated orally and kept at an ambient temperature of 22 degrees C; the surface thoracic temperature was monitored by infrared thermography. Bees were treated with the adrenergic agonists epinephrine and ephedrine, and with the beta-blocking agent alprenolol. Low doses of adrenergic agonists had no significant effect on thermogenesis, but high doses caused a hypothermia. Alprenolol triggered a dose-dependent hypothermia that was reversed by low doses of epinephrine and ephedrine. Results are discussed with reference to the metabolic and neural adrenergic pathways that may be involved in bee thermoregulation.

Time and Energy Costs of Copulation for the Sphinx Moth, Manduca sexta

In some insects copulation may represent a significant fraction of reproductive effort, yet its energetics are unexamined. The hawkmoth Manduca sexta, recognized for its endothermy and high metabolic scope (> 100), was largely quiescent during copulation, which averaged about 3 h (n = 31). However, we occasionally observed long bouts of abdominal pumping by both sexes, suggesting elevated respiratory rates. The CO₂ production of 1-d-old copulating pairs was recorded in an open-flow respirometry system and averaged 0.508 cc g⁻¹ h⁻¹ (n = 6). Comparison of these rates with the resting metabolic rates of the same males and females on the days before (0.545 cc g⁻¹ h⁻¹) and after (0.495 cc g⁻¹ h⁻¹) copulation shows that metabolic rates during copulation are not different from resting rates. Thoracic temperatures of mating moths averaged 0.31°C above ambient temperatures (n = 11), also indicating resting metabolism. Body mass measurements before and after copulation suggest that males transfer a maximum of about...

Effects of Insolation and Body Orientation on Internal Thoracic Temperature of Nymphal Melanoplus packardii (Orthoptera: Acrididae)

The effect of insolation un body temperature of nymphal Packard grasshoppers, Melanoplus packardii Scudder, was measured in the field. Live nymphs were each restrained in a series of orientations to the sun, and insolation was adjusted using a shade cloth. Internal thoracic temperature was allowed to stabilize and was compared with that of a reference nymph restrained in a sunshade. Equilibrium body temperatures of insolated nymphs exceeded that of the reference nymph by an amount (∆ T b) which increased with energy intercepted ( ENERGY ) and insect size ( SIZE ) by a relationship of the form ∆ T b = a · ENERGY · SIZEb· When insect size was expressed as mass (grams), the estimates of a and b were 18.76 and -0.312, respectively ( r 2 = 0.6198); when insect size was expressed as length (millimeters), a and b were 826.66 and −1.133, respectively ( r 2 = 0.6463) These results allow estimation of equilibrium body temperature elevation of M. packardii nymphs from solar radiation, the zenith angle of the sun, insect size, and the orientation of the insect to the sun.

Age-related variation in body temperature, thermoregulation and activity in a thermally polymorphic dragonfly

Thoracic temperatures (Tth) of Libellula pulchella dragonflies during activity in the field were compared between age classes and with laboratory measures of optimal thoracic temperature for flight performance (Tth,opt; a trait that varies during adult maturation in this species). Newly emerged adults (tenerals) had mean Tth values during flight (34.5 °C; range 29-40 °C) that did not differ from their mean Tth,opt (34.6 °C; range 28.5-43.8 °C). Mature adults had higher and more precisely regulated thoracic temperatures (mean Tth 41.7 °C; range 37.5-45.2 °C), which were somewhat lower than their mean Tth,opt (43.6 °C; range 38.7-49.9 °C). Among matures, behaviors requiring the highest levels of flight exertion (aerial copulation; mate guarding; escalated territorial contests) caused an elevation of Tth above that of concurrently sampled individuals engaged in routine flight (mean Tth difference 1.3 °C), which raised mean Tth to a level that was not significantly different from Tth,opt (42.5 versus 43.5 °C). Compared with tenerals, matures spent more time flying, made longer-duration flights and showed a more restricted pattern of daily activity. Sympatric Anax junius dragonflies that regulate Tth endothermically had a uniform pattern of activity across the entire day, i.e. occupied a broader ecological niche than that of L. pulchella. These results support the hypotheses that optimal body temperature evolves to match the elevated body temperatures that occur during exercise and that the ecological benefits of an expanded niche are a secondary benefit rather than a primary selective force during the evolution of homeothermy and high body temperatures.

Effect of Foraging Distance on the Thermal Behaviour of Honeybees during Dancing, Walking and Trophallaxis

AbstractBy means of infrared thermography and without disturbing social interactions, the correlation between thoracic temperature in honeybees, Apis mellifera carnica, upon their return to the hive and their foraging distance was investigated. Thoracic temperature while dancing and walking and during trophallactic contact with hive bees decreased with increasing flight distance. In bees foraging 0.5, 1, 1.5 and 2 molar sucrose solutions from a distance of 120 m, dancing temperature amounted to 38.4, 40.1, 40.9 and 40.6 °C, respectively; while in bees foraging from a distance of 2950 m it amounted to 36.6, 38.4, 38.6 and 39.1 °C, respectively. The rate of decrease in dancing temperature per 1000 m increase in flight distance was 0.64, 0.47, 0.81 and 0.54 °C with a 0.5, 1, 1.5 and 2 molar sucrose solution, respectively. Both at short and at long flight distances, the relationship between thoracic temperature and sucrose concentration of the food followed a non‐linear curve, which flattened at concentrations higher than 1 mol/1. The experiments showed that inside the hive the foragers' level of thermoregulation depends not only on the energy (sugar) content of the food; but rather, the level of thermoregulation corresponds to the general quality of the food source, which includes both energy content and distance from the hive. Because the thermal behaviour of foragers correlates with several behavioural parameters indicating the bees' foraging tendency and their eagerness to dance, thoracic temperature seems to be a correlate of the profitability of foraging.

Thermoregulation and Response to Competition in the African Dung Beetle Kheper nigroaeneus (Coleoptera: Scarabaeidae)

Previous studies have shown that some large African dung beetles maintain an elevated thoracic temperature while constructing and rolling dung balls, while others allow body temperature to decline to near ambient temperatures. These studies suggest a causal relationship between elevated thoracic temperature and intense competition for dung The ability for endogenous temperature regulation is well developed in Kheper nigroaeneus, a diurnal dung ball roller found in Kruger National Park, South Africa. We studied K. nigroaeneus on the dung of large herbivores during the rainy season. We here report that, although winners of conspecific contests for possession of already constructed dung balls have significantly higher thoracic temperatures than losers, K. nigroaeneus does not maintain an elevated body temperature while making or rolling dung balls under competition. Rather, K. nigroaeneus responds to inter- and intraspecific competition by reducing both ball construction time and ball volume prior to initiating ball rolling, thereby reducing potential loss of energetic investment. On arrival at fresh dung, beetles assessed both dung quality and intensity of competition and often rejected dung that had begun to dry or on which many conspecifics were already present. Alternative dung-handling strategies by other species (e.g, pellet sequestering and kleptoparasitism) are discussed.

Thermal behavior of round and wagtail dancing honeybees

The thermal behavior of round and wagtail dancing honeybees (Apis mellifera carnica) gathering sucrose solutions of concentrations between 0.5 and 2 mol·l-1 was investigated under field conditions by infrared thermography (30–506 m flight distance). During the stay inside the hive thoracic surface temperature ranged from 31.4 to 43.9 °C. In both round and wagtail dancing honeybees the concentration of sucrose in the food influenced dancing temperature in a non-linear way. Average dancing temperature was 37.9 °C in foragers gathering a 0.5 mol·l-1 sucrose solution, 40.1°C with a 1 mol·l-1, 40.6°C with a 1.5 mol·l-1 and 40.7°C with a 2 mol·l-1 solution. The variability of thoracic temperature was highest with the 0.5 mol·l-1 and lowest with the 1.5 and 2 mol·l-1 concentrations. Thoracic temperatures during trophallactic contact with hive bees were similar to dancing temperature at 1.5 mol·l-1 but lower at the other concentrations. During periods of distribution of food to hive bees (trophallactic contact >2.5s) the dancers' thorax cooled down by more than 0.5°C considerably more frequently with the 0.5 mol·l-1 solution (65% of cases) than with the 1.5 mol·l-1 solution (26%). By contrast, heating the thorax up by more than 0.5°C was infrequent with the 0.5 mol·l-1 solution (2%) but occurred at a maximum rate of 26% with the 1.5 mol·l-1 solution. Bees gathering the 1 or 2 mol·l-1 solutions showed intermediate behavior. Linear model analysis showed that at higher concentrations the dancers compensated better for variations of hive air temperature: per 1 °C increase of hive temperature dancing temperature increased by 0.34, 0.22, 0.12, and 0.13 °C with 0.5, 1, 1.5, and 2 mol·l-1 sucrose solutions, respectively. The results furnish evidence that dancing honeybees follow a strategy of “selective heterothermy” by tuning their thermal behavior to the needs of the behavior performed at the moment. Thoracic temperature is regulated to a high level and more accurately when fast exploitation of profitable food sources is recommended. Thoracic temperature is lowered when the ratio of gain to costs of foraging becomes more unfavorable.

Simultaneous control of head and thoracic temperature by the green darner dragonfly Anax junius (Odonata: Aeshnidae)

Anax junius is a large dragonfly that regulates thoracic temperature (Tth) during flight. This species, like several other intermittently endothermic insects, achieves control of Tth at least in part by increasing circulation of hemolymph to the abdomen at high air temperature (Ta), thus facilitating heat loss from the thorax. In this paper, I demonstrate that heat transfer to the head is also under active control, very probably owing to temperature-sensitive alteration of hemolymph circulation. As a result, head temperature (Th) is strikingly elevated above Ta during endothermic warm-up and flight. Furthermore, during unrestrained flight in the field, Th is regulated actively by increasing hemolymph circulation from the warm thorax at low Ta. Concurrent measurements of abdominal temperature (Tab) confirm that the abdomen is used as a 'thermal window' at Ta>30 °C but apparently not at lower Ta; thus, some additional mechanism(s) must exist for regulation of Tth at low Ta.

Large-scale changes in thermal sensitivity of flight performance during adult maturation in a dragonfly

Newly emerged adult dragonflies are physiologically immature in a number of ways, including the mass, ultrastructure and biochemistry of their flight muscles. In Libellula pulchella dragonflies, adult maturation of flight muscle is accompanied by striking changes in thermal physiology. Vertical force production during fixed flight attempts in newly emerged adults (tenerals) shows a broad plateau of near-peak performance, first attained at cool thoracic temperatures (typically 28­34 °C) and maintained up to thoracic temperatures of 40­45 °C [mean optimal thoracic temperature (OTT)=34.6 °C; mean upper lethal temperature (ULT)=45.3 °C]. In contrast, fully mature adults show narrow thermal sensitivity curves, wherein peak performance is approached only within a few degrees of the thermal optimum, which invariably occurs at hot thoracic temperatures (38­50 °C; mean OTT=43.5 °C; mean ULT=48.6 °C). These changes in the shape and position of thermal performance curves are compared with predictions from hypotheses for the evolution of thermal sensitivity.

Foraging and courtship behaviour in males of the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae): thermal physiology and the roles of body size

Abstract. The effects of climate and body size on male behaviour were examined in the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae), which shows resource‐based polygyny at floral food sources in Britain in spring. Larger males are able to fly at lower temperatures than smaller males, and can therefore court females under conditions in which smaller males cannot fly. This is predicted from patterns of endothermic ability at low temperatures already demonstrated within this species. Video analysis of male competition for opportunities to initiate courtship with tethered females showed that larger males are also competitively superior, and can displace smaller males from favoured flight positions immediately behind females. The mating system shown by male A plumipes is strongly dependent on male density. At low densities, males show exclusive territoriality at floral sources. As male density increases, this strategy is abandoned in favour of patrolling with considerable spatial overlap between males, and opportunistic Polygyny. Despite high endothermic abilities, male behaviour is highly dependent on weather, and particularly ambient temperature. Males bask in the early morning and maintain high thoracic temperatures. Temperature data from freshly killed bees show that thoracic warming from solar sources effectively doubles the thermogenic power generated by the bee alone at low ambient temperatures. Male strategies in A.plumipes are compared to female responses to climate. Having controlled for differences in body size there is no difference in endothermic abilities between the sexes. Males do not, however, fly under conditions in which females of the same size would remain active. These results are discussed in the light of differential dependence of reproductive success on flight activity for the two sexes.

Ecophysiology, Range Contraction and Survival of a Geographically Restricted African Dung Beetle (Coleoptera: Scarabaeidae)

1. Habitat degradation and the overexploitation of many taxa currently represent serious threats to biological diversity. In species-rich foodwebs, trophically specialized species are particularly prone to risk if their prey species are removed. This appears to be true of Circemllium bacchus (Scarabaeinae: Canthonini), a large, flightless dung beetle, which feeds on the dung of large mammals such as elephant, buffalo and rhinoceros. It was once widespread in the southern African savanna but within the last century has become restricted to a small, xeric area in the south-eastern Cape Province of South Africa. In this study we examine the original distribution of this species and reasons for its subsequent range contraction. 2. Because temperature and water availability play such important roles in determining the abundance and distribution of animals, and because the thermal biology of dung beetles is so important in determining their competitive ability, we compare the desiccation resistance and thermal biology of C. bacchus with a large, winged, savanna dung beetle, Pachylomerus femoralis, as well as that reported in the literature for other dung beetles. We also compare respiratory metabolism of the two species because an elevated factorial aerobic scope is indicative of competitive superiority. In addition, we compare the distribution and habitat preference of C. bacchus with that of closely related scarabaeine beetles to gain insight into its original distribution. 3. Circellium bacchus appears to have originated in mesic, east-coast wooded savanna and forests. It is unlike any other large dung beetle because its flightless condition makes it a strict ectotherm. This means that it stands little chance in competing for dung with heterothermic, winged dung beetles which have a competitive advantage at dung pads. This advantage is conferred on winged species because of high post-flight activity levels associated with high thoracic temperatures. 4. The penetration of other, wooded savanna areas by C. bacchus is ascribed to the presence of a constant dung source which would ameliorate the effects of competition from other dung beetles. The only known resource of this type is Black Rhinoceros middens. Range contraction of the Black Rhinoceros seems to have precipitated range contraction of C. bacchus. Collection records of C. bacchus correspond with areas known to have supported Black Rhinoceros populations throughout this century. 5. The survival of C. bacchus in the xeric southern and eastern Cape seems to have been a result both of its large body size, which has endowed it both with a lower conductance and greater desiccation resistance than other savanna-dwelling dung beetles, and the presence of a small population of elephants in the thick Valley Bushveld of the eastern Cape throughout this century