Metabolic rate and thermoregulation in two species of tuco-tuco, Ctenomys talarum and Ctenomys australis (Caviomorpha, Octodontidae)

1. Resting metabolic rate and body temperature in function of ambient temperature were determined for two species of Ctenomys. 2. Oxygen consumption was lowest between 25 and 30 degrees C and was 0.946 +/- 0.030 and 0.968 +/- 0.022 in Ctenomys talarum (from Mar de Cobo and Necochea, respectively). Resting metabolic rate was 0.343 +/- 0.053 at 30 C in C. australis. 3. Mean rectal temperature at thermoneutrality was 36.1 +/- 0.13 and 37.3 +/- 0.17 in C. talarum and C. australis, respectively. 4. Limited thermoregulation occurred in C. talarum down to 20 degrees C but C. australis maintained body temperature down to 10 degrees C. 5. Both species of tuco-tucos became hyperthermic at ambient temperatures above thermoneutrality.     

Control of local heat gain by vasomotor response of the hand

Finger blood flow (BF) was measured by venous occlusion plethysmography using mercury-in-Silastic strain gauges during immersion of one hand in hot water (raised by steps of 2 degrees C every 10 min from 35 to 43 degrees C), the other being a control (kept immersed in water at 35 degrees C). The measurements were made in three different thermal states on separate days: 1) cool-25 degrees C, 40% rh, esophageal temperature (Tes) = 36.64 +/- 0.10 degrees C; 2) warm-35 degrees C, 40% rh, Tes = 36.71 +/- 0.11 degrees C; and 3) hot-35 degrees C, 80% rh with the legs immersed in water at 42 degrees C, Tes = 37.26 +/- 0.11 degrees C. When water temperature was raised at 42 degrees C, Tes = 37.26 +/- 0.11 When water temperature was raised to 39-41 degrees C in the warm state, finger BF in the hand heated locally (BFw) decreased. When water temperature was raised to 43 degrees C, however, BFw returned to the control value. In the hot state, Tes rose steadily, reaching 37.90 +/- 0.12 degrees C at the end of the 50-min sessions. BF in the control finger also increased gradually during the session. BFw showed a tendency to decrease when water temperature was raised to 39 degrees C, but the change was not greater than that observed in the warm state. In the cool state, no such reduction in BFw was observed when water temperature was raised to 39-41 degrees C. On the contrary, BFw increased at water temperatures of 41-43 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Social versus individual behaviour: a comparative approach to thermal behaviour of the honeybee (Apis mellifera L.) and the American cockroach (Periplaneta americana L.)

To study the relationship between the individual and social thermoregulatory behaviour, we used honeybee workers and American cockroaches. Single insects or groups of 10-20 individuals were placed in a temperature gradient chamber, and their thermal preference was recorded for 48 h under natural summer photoperiod. Single bees showed diurnal changes in selected ambient temperature, which culminated at 14:00 reaching 34+/-2 degrees C, and then slowly decreased, reaching a nocturnal minimum of 28+/-2 degrees C at 04:00. In contrast, the zenith of temperature selected by groups of bees (31+/-1 degrees C) was reached at 04:00 and the nadir (29+/-2 degrees C) was recorded at 14:00. Groups of bees clustered together during the night time, and dispersed during intense day time activity. Such changes were absent in groups of cockroaches. Cockroaches selected an ambient temperature of 30+/-1 degrees C both during day and night. In conclusion, there is a striking analogy in the diurnal thermal behaviour between a colony of bees and mammals. During their nychthemeral rest phase, both of them select higher temperatures than during the activity phase and, simultaneously, they reduce their overall surface area of heat loss to conserve metabolic heat. Therefore, the colony behaves as a homeothermic superorganism. In contrast, a single bee, isolated from the colony, utilizes a heterothermic strategy to save energy for a morning warm up.     

Effects of environmental cooling on force production in the quadriceps and hamstrings

The purpose of this study was to determine the effects of environmental cooling on force production in the quadriceps and hamstring muscles. Ten men (mean +/- SD: age = 21.4 +/- 2.2 years, height = 168.5 +/- 35.9 cm, body mass = 78.0 +/- 6.4 kg) participated in this study. Each subject completed 2 sets of 10 maximal effort repetitions on a Cybex II isokinetic dynamometer at 3.14 rad x s(-1). Between sets, subjects sat in environmental temperatures of 20, 15, 10, or 5 degrees C for 40 minutes. A significant decrease (p 相似文献   

Heat exchange of the rat in thermoneutral zone temperature and comparison with heat exchange in ambient temperature over and under it

With the help of thermonetry and general calorimetry body temperature and heat production in ambient temperatures 20 degrees C, 28 degrees C, 33 degrees C were recorded. The experiments showed, that at the temperature 20 degrees C the rectal temperature was changing very little. But in ambient temperature 33 degrees C the rectal temperature was 40.5 +/- 0.1 degrees C.     

Body temperature and oxygen uptake in the kinkajou (Potos flavus, Schreber), a nocturnal tropical carnivore.

Two kinkajous (Potos flavus, Procyonidae) showed marked nycthemeral variations in their rectal temperature. The mean Tr at night was 38.1 +/- 0.4 degrees C SD and 36.0 +/- 0.6 degrees C SD while resting during the day. Body temperature and O2-consumption were measured at ambient temperatures from 5-35 degrees C. With one exception at 35 degrees C, hypo- or hyperthermia was never observed. At air temperatures above 30 degrees C the bears reacted with behavioural responses. O2-consumption was minimal at Ta's from 23-30 degrees C. The mean basal metabolic rate was 0.316 ml O2 g-1 h-1 which is only 65% of the expected value according to the Kleiber formula. Below 23 degrees C heat production followed the equation : y (ml O2 g-1 h-1) = 0.727--0.018 Ta. The minimal thermal conductance was 90% of the predicted value according to the formula : C (ml O2 g-1 h-1 degrees C-1) = 1.02 W-0.505 (HERREID & KESSEL, 1967). Kinkajous are another distinct exception to the mouse to elephant curve.     

茄子光系统Ⅱ的热胁迫特性

以耐热性较弱的黑贝一号圆茄和耐热性较强的黑贝二号圆茄为试材,热胁迫处理后采用植物效率仪PEA进行快速叶绿素荧光诱导曲线及其参数测定.结果表明：当温度高于40 ℃,PSⅡ结构受热胁迫影响较为敏感,表现为初始荧光F_o缓慢上升;PSⅡ原初光化学效率F_v/F_m和ΔF/F_m′大幅度下降,且黑贝二号F_v/F_m的半衰时间T₅₀和ΔF/F_m′的半衰温度t₅₀分别大于黑贝一号.较高的热胁迫剂量（48℃处理5 min或44℃处理20～30min）下,快速荧光诱导动力学曲线呈现OKJIP型,在700μs处出现与放氧复合体失活有关的K相.黑贝一号在44 ℃下处理20 min才有K相出现,黑贝二号则晚10 min出现.与35℃相比,在48℃,特别是在52℃的较高剂量热胁迫下,Strasser能量流动模型参数中的DI_o/RC有大幅度地增加,体现了热耗散对PSⅡ的较强保护能力.随着热胁迫温度的升高和热胁迫时间的延长,两品种的无活性中心F_vi/Fv显著增加.     

Metabolic physiology of the numbat (Myrmecobius fasciatus)

The numbat (Myrmecobius fasciatus) is unique amongst marsupials as it is exclusively diurnal, feeds only on termites and is semi-fossorial. This study examines the thermal and metabolic physiology of the numbat to determine if its physiology reflects its phylogeny, diet and semi-fossorial habit. Numbats (mean adult body mass 552 g) were able to regulate body temperature at ambient temperatures of 15-30 degrees C, with a body temperature at thermoneutrality (30 degrees C) of 34.1 degrees C. The thermoneutral body temperature was not significantly different from that predicted for an equivalent-sized marsupial. Basal metabolic rate, measured at 30 degrees C, was 0.389 +/- 0.025 ml O(2) g(-1) h(-1), and was slightly but not significantly lower at 82.5% of that predicted for a typical marsupial of equivalent body mass. Metabolic rate increased with decreasing ambient temperatures below 30 degrees C. Patterns of metabolic cycling observed for completely inactive numbats at ambient temperatures below 30 degrees C are likely to be related to sleep phase. Wet thermal conductance of 1.94 J g(-1) h(-1) degrees C(-1) (at 30 degrees C) was 131% of that predicted for a marsupial. Evaporative water loss of the numbat remained constant below the thermoneutral zone (<30 degrees C) at approximately 0.6 ml g(-1) h(-1), only 47.4% of that predicted for a marsupial. It increased to 1.01 +/- 0.16 ml g(-1) h(-1) at an ambient temperature of 32.5 degrees C. The thermal and metabolic physiology of the numbat is generally similar to that expected for other marsupials, and is also comparable to that of termitivorous placental mammals. Thus the reduction in body temperature and basal metabolic rate of placental termitivores is a "marsupial-like" low energy turnover physiology, and the numbat being a marsupial already has an appropriate physiology to survive exclusively on a low energy diet of termites.     

Hypothermia versus torpor in response to cold stress in the native Australian mouse Pseudomys hermannsburgensis and the introduced house mouse Mus musculus

This study compared torpor as a response to food deprivation and low ambient temperature for the introduced house mouse (Mus musculus) and the Australian endemic sandy inland mouse (Pseudomys hermannsburgensis). The house mouse (mass 13.0+/-0.48 g) had a normothermic body temperature of 34.0+/-0.20 degrees C at ambient temperatures from 5 degrees C to 30 degrees C and a basal metabolic rate at 30 degrees C of 2.29+/-0.07 mL O2 g(-1) h(-1). It used torpor with spontaneous arousal at low ambient temperatures; body temperature during torpor was 20.5+/-3.30 degrees C at 15 degrees C. The sandy inland mouse (mass 11.7+/-0.16 g) had a normothermic T(b) of 33.0+/-0.38 degrees C between T(a) of 5 degrees C to 30 degrees C, and a BMR of 1.45+/-0.26 mL O2 g(-1) h(-1) at 30 degrees C. They became hypothermic at low T(a) (T(b) about 17.3 degrees C at T(a)=15 degrees C), but did not spontaneously arouse. They did, however, survive and become normothermic if returned to room temperature (23 degrees C). We conclude that this is hypothermia, not torpor. Consequently, house mice (Subfamily Murinae) appear to use torpor as an energy conservation strategy whereas sandy inland mice (Subfamily Conilurinae) do not, but can survive hypothermia. This may reflect a general phylogenetic pattern of metabolic reduction in rodents. On the other hand, this may be related to differences in the social structure of house mice (solitary) and sandy inland mice (communal).     

Future CO2 concentrations, though not warmer temperatures, enhance wheat photosynthesis temperature responses

The temperature dependence of C3 photosynthesis is known to vary according to the growth environment. Atmospheric CO2 concentration and temperature are predicted to increase with climate change. To test whether long-term growth in elevated CO2 and temperature modifies photosynthesis temperature response, wheat (Triticum aestivum L.) was grown in ambient CO2 (370 micromol mol(-1)) and elevated CO2 (700 micromol mol(-1)) combined with ambient temperatures and 4 degrees C warmer ones, using temperature gradient chambers in the field. Flag leaf photosynthesis was measured at temperatures ranging from 20 to 35 degrees C and varying CO2 concentrations between ear emergence and anthesis. The maximum rate of carboxylation was determined in vitro in the first year of the experiment and from the photosynthesis-intercellular CO2 response in the second year. With measurement CO2 concentrations of 330 micromol mol(-1) or lower, growth temperature had no effect on flag leaf photosynthesis in plants grown in ambient CO2, while it increased photosynthesis in elevated growth CO2. However, warmer growth temperatures did not modify the response of photosynthesis to measurement temperatures from 20 to 35 degrees C. A central finding of this study was that the increase with temperature in photosynthesis and the photosynthesis temperature optimum were significantly higher in plants grown in elevated rather than ambient CO2. In association with this, growth in elevated CO2 increased the temperature response (activation energy) of the maximum rate of carboxylation. The results provide field evidence that growth under CO2 enrichment enhances the response of Rubisco activity to temperature in wheat.     

Body temperature changes induced by huddling in breeding male emperor penguins

Huddling is the key energy-saving mechanism for emperor penguins to endure their 4-mo incubation fast during the Antarctic winter, but the underlying physiological mechanisms of this energy saving have remained elusive. The question is whether their deep body (core) temperature may drop in association with energy sparing, taking into account that successful egg incubation requires a temperature of about 36 degrees C and that ambient temperatures of up to 37.5 degrees C may be reached within tight huddles. Using data loggers implanted into five unrestrained breeding males, we present here the first data on body temperature changes throughout the breeding cycle of emperor penguins, with particular emphasis on huddling bouts. During the pairing period, core temperature decreased progressively from 37.5 +/- 0.4 degrees C to 36.5 +/- 0.3 degrees C, associated with a significant temperature drop of 0.5 +/- 0.3 degrees C during huddling. In case of egg loss, body temperature continued to decrease to 35.5 +/- 0.4 degrees C, with a further 0.9 degrees C decrease during huddling. By contrast, a constant core temperature of 36.9 +/- 0.2 degrees C was maintained during successful incubation, even during huddling, suggesting a trade-off between the demands for successful egg incubation and energy saving. However, such a limited drop in body temperature cannot explain the observed energy savings of breeding emperor penguins. Furthermore, we never observed any signs of hyperthermia in huddling birds that were exposed to ambient temperatures as high as above 35 degrees C. We suggest that the energy savings of huddling birds is due to a metabolic depression, the extent of which depends on a reduction of body surface areas exposed to cold.     

Studies on plasma free-fatty-acid metabolism and triglyceride synthesis of brown adipose tissue in vivo during cold-induced thermogenesis of the newborn rabbit.

Parameters of plasma free fatty acid metabolism (pool size, half time, disappearance rate, turnover time and absolute turnover rate), the influx of plasma free fatty acids into the glycerides of brown adipose tissue and the pathway of triglyceride synthesis in brown adipose tissue (glycerol-1-phosphate versus monoglyceride pathway) were examined after intravenous injection of [1-14C]palmitate in newborn rabbits. In the thermoneutral environment of 35 degrees C the turnover rate of plasma free fatty acids was 10.20 mumol/min per 100 g body weight and its flux into the glycerides of brown adipose tissue 0.367 mumol/min per 100 g body weight. Cold exposure at an ambient temperature of 20 degrees C caused a decrease to 5.84 mumol/min and 0.207 mumol/min per 100 g body weight, respectively. Both under basal conditions at an ambient temperature of 35 degrees C and under cold-induced thermogenesis at an ambient temperature of 20 degrees C triglyceride synthesis in brown adipose tissue ran through the glycerol 1-phosphate pathway.     

Growth and formation of toxin by Clostridium botulinum in peeled, inoculated, vacuum-packed potatoes after a double pasteurization and storage at 25 degrees C

A process that claims to use a double pasteurization to produce vacuum-packed potatoes for storage at ambient temperature has been evaluated. After the first pasteurization, potatoes are vacuum-packed and stored at 25 degrees-35 degrees C for up to 24 h, which is intended to allow germination of bacterial spores, and are then pasteurized again. When potatoes were inoculated with spores of Clostridium botulinum and subjected to this double-pasteurization process a high proportion of spores remained viable and resulted in growth and formation of toxin within 5-9 d at 25 degrees C. To provide an appropriate reduction in the risk o survival and growth of Cl. botulinum, peeled, vacuum-packed potatoes for storage at ambient temperature should be given a heat treatment equivalent to an F(0)3 process. If they are not given such a heat treatment they should be stored at a temperature below 4 degrees C.     

Effect of ovary holding temperature and time on equine granulosa cell apoptosis, oocyte chromatin configuration and cumulus morphology

The effects of ovary holding time and temperature on granulosa cell apoptosis, oocyte chromatin configuration and cumulus morphology were investigated through a series of experiments. Three experiments were performed to determine the effect of ovary holding time and temperature on granulosa cell apoptosis. Ovaries were held (1) at 20, 30 or 35-37 degrees C for up to 2h, (2) at 30 degrees C for 0-1, 1-2, 2-3, 3-4, 4-6 or 6-10h, and (3) granulosa cells were held for 0, 1, 2, 3, 5, 12 or 24h in M199 with Hank's salts at room temperature (suboptimal incubation). Granulosa cell DNA was analysed by ethidium bromide staining or 3'-end labelling. Two experiments were performed to determine the effect of ovary holding time and temperature on oocyte chromatin configuration. Ovaries were held (1) at 20, 30 or 35-37 degrees C for up to 3h and (2) at 20-37 degrees C for 0-1, 1-2, 2-3, 3-4, 4-6, 6-8 or 8-12h. The oocytes were stained with Hoechst stain 33258 and the chromatin configuration was evaluated. Two experiments were performed to determine the effect of ovary holding time and temperature on cumulus oophorus morphology. Ovaries were held at (1) 20-30 or 35-37 degrees C for up to 2h and (2) for 0-2, 2-4, 4-6, and 6-10h at 35-37 degrees C. The cumulus oocyte complex (COC) were retrieved and the cumulus morphology was evaluated. There was no difference in proportion of follicles with non-apoptotic granulosa cells in the two groups below body temperature (20 and 30 degrees C), but more follicles had apoptotic granulosa cells when the ovaries were held at 35-37 degrees C (P < 0.001). Holding ovaries at 30 degrees C for more than 3h increased the proportion of follicles with apoptotic granulosa cells (P < 0.01). When follicles with non-apoptotic granulosa cells were incubated at room temperature, there was no granulosa cell apoptosis in any of the follicles within the first 3h, but at 5h apoptosis was present in the granulosa cells of 22% of the follicles, and 78% of the follicles contained apoptotic granulosa cells at 24h (P < 0.001). The temperature at which the ovaries were held did not influence oocyte chromatin, although there was a tendency towards more condensed chromatin configurations in the groups below body temperature. More denuded and expanded COCs were present in the lower temperature group (P < 0.001). Oocyte chromatin configuration changed after 6h of holding (P < 0.001), and numbers of compact COCs decreased after 2h (P < 0.05). The present studies suggest that equine follicles should be held for no more than 3h at 20-30 degrees C if granulosa cell apoptosis is to be avoided. To avoid changes in cumulus oophorus morphology, ovaries should be held at 35-37 degrees C and for less than 2h before processing, and to avoid oocyte chromatin configuration changes, ovaries should be stored for less than 6h. When ovaries are to be used in oocyte maturation studies, and assuming that (1) CC is the chromatin configuration of choice for oocyte maturation, (2) that presence of granulosa cell apoptosis promotes maturation of the oocyte and (3) that expanded cumulus oocytes are preferable, the present data suggests that ovaries should be stored for 4-6h before oocyte retrieval.     

Heat loss from the human head during exercise

Evaporative and convective heat loss from head skin and expired air were measured in four male subjects at rest and during incremental exercise at 5, 15, and 25 degrees C ambient temperature (Ta) to verify whether the head can function as a heat sink for selective brain cooling. The heat losses were measured with an open-circuit method. At rest the heat loss from head skin and expired air decreased with increasing Ta from 69 +/- 5 and 37 +/- 18 (SE) W (5 degrees C) to 44 +/- 25 and 26 +/- 7 W (25 degrees C). At a work load of 150 W the heat loss tended to increase with increasing Ta: 119 +/- 21 (head skin) and 82 +/- 5 W (respiratory tract) at 5 degrees C Ta to 132 +/- 27 and 103 +/- 12 W at 25 degrees C Ta. Heat loss was always higher from the head surface than from the respiratory tract. The heat losses, separately and together (total), were highly correlated to the increasing esophageal temperature at 15 and 25 degrees C Ta. At 5 degrees C Ta on correlation occurred. The results showed that the heat loss from the head was larger than the heat brought to the brain by the arterial blood during hyperthermia, estimated to be 45 W per 1 degree C increase above normal temperature, plus the heat produced by the brain, estimated to be up to 20 W. The total heat to be lost is therefore approximately 65 W during a mild hyperthermia (+1 degrees C) if brain temperature is to remain constant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Venous return from distal regions affects heat loss from the arms and legs during exercise-induced thermal loads

To study the role of venous return from distal parts of the extremities in influencing heat loss from the more proximal parts, changes in mean skin temperature (Tsk) of the non-exercising extremities were measured by color thermography during leg and arm exercise in eight healthy subjects. Thirty minutes of either leg or arm exercise at an ambient temperature (Ta) of 20 degrees C or 30 degrees C produced a greatly increased blood flow in the hand or foot and a great increase in venous return through the superficial skin veins of the extremities. During the first 10 min of recovery from the exercise, blood flow to and venous return from the hand or foot on the tested side was occluded with a wrist or ankle cuff at a pressure of 33.3 kPa (250 mm Hg), while blood flow to the control hand or foot remained undisturbed. During the 10-min wrist occlusion, Tsk increased significantly from 28.3 degrees +/- 0.41 degrees C to 30.1 degrees +/- 0.29 degrees C in the control forearm, but remained at nearly the same level (28.0 degrees +/- 0.34 degrees C to 28.2 degrees +/- 0.25 degrees C) in the occluded forearm. In the legs, although Tsk on both sides was virtually identical (32.0 degrees +/- 0.31 degrees C, control vs 32.0 degrees +/- 0.36 degrees C, tested) before occlusion, Tsk on the control side (32.6 degrees +/- 0.27 degrees C) was significantly higher than that on the tested side (32.2 degrees +/- 0.21 degrees C) after ankle occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of short-time period of an adaptation to decreased ambient temperature on interleukin-6 and corticosterone levels in female Wistar strain rats in the proestrous phase of the reproductive cycle

To date, there has been little research examining whether short-time changes of external environmental conditions exert any effects on immune responses. The activation of metabolic changes, release of hormones responsive for immunomodulation and the action of interleukins play an important role in interaction with hormones of an anterior pituitary gland in the proestrous phase of the reproductive cycle. The aim of our study was to determine the effects of a short-time change of ambient temperature (30 minutes) on interleukin-6 (IL-6) and corticosterone plasma concentration of female rats in the proestrous phase of the reproductive cycle. The climatic chamber with automatically adjustable and monitored internal environmental parameters (temperature, oxygenation, humidity) was used during the experiment. The estimation of the vaginal lavage using a microscope was done to determine the estrous cycle. On the day of the experiment, animals were divided into 2 groups: the control group (ambient temperature 21 degrees C +/- 1 degrees C; normoxia 21% O2) and the test group (ambient temperature 10 degrees C +/- 1 degrees C; normoxia 21% O2) stayed in the climatic chamber for 30 minutes. The blood samples were collected before the experiment and after 30, 60, 90, 150 and 210 minutes from the beginning of the experiment. The concentrations of IL-6 and corticosterone were measured in blood plasma samples using ELISA method. There was a significant elevation of IL-6 levels after staying in 10 degrees C during the first 150 minutes from the beginning of the experiment, with the highest value occurring after 60 minutes (426.6 pg/ml; SE - 146.1) with comparison to the value at first sampling (108.5 pg/ml; SE - 29.5; p<0.05) and with comparison to the control group at the same time from the beginning of the experiment (87.6 pg/ml; SE - 2.3; p<0.05). The changed level of corticosterone in the test group in comparison to control group was observed but the differences were insignificant. Our observations confirm the proposition, that even short-time changes of ambient conditions can activate adaptation mechanisms in the organism, which in part, is the activation of the immune system.     

The effects of ligation of the oesophagus on body and brain temperature in pigeons

1. We measured brain and colonic temperatures in adult pigeons (Columba livia) with or without oesophageal ligation, and with or without simultaneous eye covering at ambient temperatures between 24 degrees C and 45 degrees C. 2. Colonic and brain temperatures rose at the higher ambient temperatures; the temperature elevations were no different in pigeons with oesophageal ligation, compared to sham-operated controls. The presence of simultaneous eye covering also had no effect on colonic or brain temperatures. 3. Oesophageal inflation decreased from a rate of 2.8 +/- 1.4 per minute (mean +/- SEM) to zero, in anaesthetized pigeons when warmed from a colonic temperature of 40.5 degrees C to 43.8 degrees C. 4. In pigeons oesophageal inflation plays no significant part in body temperature regulation or in the maintenance of a lower brain than body temperature even in hot ambient conditions.     

Effect of high temperature and water stress on in vitro germination and growth in isolates of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin

In non-irrigated agricultural fields in tropical zones, high temperature and water stress prevail during the main cropping season. Natural epizootics of Beauveria bassiana on lepidopteran pests occur during winter. Application of B. bassiana during hot months when pest populations are at their climax may prove an effective management strategy. Therefore, 29 isolates of B. bassiana were tested for their ability to germinate and grow in temperature and water availability conditions prevailing during the pest season in these fields. The effect of temperature cycles with 8 h duration of high temperature fluctuating with 16 h duration of lower temperature (similar to field conditions); low water availability; and a combination of these two stress conditions was studied. Germination and growth assays were done at fluctuating temperature cycles of 32, 35, 38, and 42+/-1 degrees C (8 h)/25+/-1 degrees C (16 h) and in media with water stress created by 10, 20, 30, and 40% polyethylene glycol (PEG 6000). Assays set at a continuous temperature of 25+/-1 degrees C with no PEG in the medium served as controls. Stress was assessed as percentage germination or as growth relative to control. Isolates showing 90% growth relative to the control at temperature cycles including high temperatures of 35 and 38+/-1 degrees C were identified. One isolate (ARSEF 2860) had a thermal threshold above 43 degrees C. At 25 degrees C, all but one isolate of B. bassiana showed >90% growth relative to the control in 10% PEG (-0.45 MPa). Some isolates were found with >90% growth relative to control in medium having 30% PEG with water availability (1.33 MPa), nearly equivalent to that in soils which induce permanent wilting point of plants. When isolates that showed >90% growth relative to the control at both stress conditions, were stressed simultaneously, a decrease in growth was observed. Growth was reduced by approximately 20% at 35+/-1 degrees C (8 h)/25+/-1 degrees C (16 h) and 10% PEG and was affected to a greater degree in combinations of harsher stress conditions. The isolate ARSEF 2860 with a thermal threshold of >43 degrees C showed approximately 80% relative growth at a combined stress of 38+/-1 degrees C (8 h)/25+/-1 degrees C (16 h) and 10% PEG. These findings will aid the selection of isolates for use in field trials in hot or dry agricultural climates.