Aspects of the biology of Glaciopsyllus antarcticus (Siphonaptera: Ceratophyllidae) during the breeding season of a host (Fulmarus glacialoides)

Summary The breeding period of the Antarctic flea, Glaciopsyllus antarcticus (Smit and Dunnet), was synchronised with the breeding period of the host, Southern Fulmar (Fulmarus glacialoides Smith). Although eggs were laid in the host nest, larvae developed amongst the down (particularly on the belly) of host chicks. Larvae were blood feeders and pupated amongst the down of host chicks. The development of pupae was arrested by ambient temperatures (mean temperature of +2.5°C in January), but recommenced when pupae were warmed. Female fleas comprised 55.8% of a collection of 1988 adults. Low numbers of adult fleas were found in nests prior to host breeding and subsequent to host fledging in comparison to numbers on the host; adults are therefore presumed to overwinter on the host, remote from the nest.     

Thermoregulation dynamics in commercially reared colonies of the bumblebee Bombus terrestris

Thermoregulation, that is, the active control of temperature, is key to ensure proper brood development in both wild and captive bumblebee nests. In this study, thermoregulation dynamics were assessed relative to colony age and ambient temperature using commercially reared Bombus terrestris L. (Hymenoptera, Apidae, Bombus) colonies. We observed a positive relationship between brood and nest temperatures in response to ambient temperature. Thermoregulation investment (by either brooding or fanning) was lowest at brood surface temperatures between 33 and 34 °C and ambient temperatures between 28 and 32 °C. Brood temperature was less stable and thermoregulation investment higher in younger colonies, especially at lower ambient temperatures. Furthermore, queens initiated colonies sooner and colonies developed faster when kept at an ambient temperature of 29 °C as compared to 24 °C. Our results suggest that ambient temperatures are ideally kept between 29 and 31 °C.     

Effect of hypoxia and its repercussions in packing pupae of the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) for shipment

Hypoxia periods of 6, 12, 24, 48, and 72?h combined with temperatures of 15°C, 20°C and 25°C were applied to Diachasmimorpha longicaudata pupae in packaging conditions. Alternating temperatures of 26–20–26°C were applied to pupae in three sequential 4-h periods less than 12?h of hypoxia, and the effect of hypoxia on the pupae was evaluated under ambient conditions in commercial shipping. The emergence, longevity, fecundity and flight ability of adult parasitoids were recorded. The duration of hypoxia (>24?h) and the higher temperature (25°C) significantly reduced the emergence and longevity of adults. The different temperatures, including the variation in temperature combined with hypoxia, showed no significant effect on fecundity or flight ability. The temperature and humidity recorded during commercial shipping under hypoxia did not show any effect on the emergence of parasitoids. As a consequence, hypoxia was only notably significant after 24?h, which occasionally occurs in practical packaging processes. The use of hypoxia for shipping D. longicaudata pupae can be widely recommended, but long shipping periods and high temperatures should still be avoided.     

Survival of Heleomyza borealis (Diptera, Heleomyzidae) larvae down to − 60°C

Heleomyza borealis Boh. (Diptera, Heleomyzidae) overwinters as larvae in Arctic habitats, where they may experience winter temperatures below ? 15°C. The larvae freeze at c.? 7°C but in acclimation experiments 80% survived when exposed to ? 60°C. Of the larvae exposed to between ? 4 and ? 15°C, only 3% pupated. However, when cooled to ? 20°C this increased to 44%, with 4% emerging as adults. Larvae maintained at 5°C contained low levels of glycerol, sorbitol and trehalose, which did not increase with acclimation to low temperatures. However, levels of fructose increased from 6.1 μg mg^?1 fw in control animals to 17 μg mg^?1 fw when exposed to ? 2°C for 1 week. Larval body water (2.2 ± 0.1 g/g dw, mean ± SD, n = 100) and lipid content (0.22 ± 0.002 g/g fw, mean ± SE) showed no significant change during acclimation to low temperatures. Larvae maintained at a constant 5°C survived for over 18 months with little loss of body mass (from 7.5 ± 1.2 to 7.0 ± 1.2 mg fw, mean ± SD, n = 20), but none pupated. Heleomyza borealis larvae appear to feed and grow until they reach a body mass of about 7.5 mg and then become dormant. They remain in this state until they experience a low temperature stimulus (< ? 15°C) followed by a warm period (≈ 5°C). This ensures that the larvae pupate and adults emerge in early summer, allowing the maximum growing period before the following winter. Heleomyza borealis are adapted to survive long winters in a dormant larval state. They have a low metabolic rate, can conserve body water even at subzero temperatures but do not synthesize large quantities of cryoprotectants.     

The effects of temperature on development of the large narcissus fly (Merodon equestris)

Eggs, larvae, pupae and adults of the large narcissus fly (Merodon equestris) were reared at a series of constant temperatures between 9–24°C. Egg development required from 37 days at 9°C to 7 days at 21.5°C. The low-temperature threshold for development was 6.7°C. Larvae reared at 1424°C were fully-grown after 18 weeks, but it took much longer for such insects to pupate, and adult flies emerged only after about 45 weeks of development. Large narcissus flies enter diapause during the larval stage and overwinter as fully-fed larvae, forming pupae in the following spring. Post-winter pupation and pupal development took from 169 days at 10°C to 36 days at 21.5°C. Of this, pupal development required from 91 days at 10°C to 19 days at 21.5°C. The low-temperature threshold for post-winter pupation and pupal development was 7.1°C, and for pupal development alone, 7.2°C. Females maintained at or below 19°C laid few eggs, whereas some females kept at or above 21.5°C laid more than 100 eggs (mean 69 ± 36). Approximately 50% of females maintained at or above 21.5°C laid less than 10 eggs during their lifetime. The mean egg-laying time was 6 to 9 days. Although temperatures at or below 19°C inhibited mating, once a female had mated, such temperatures did not prevent oviposition.     

Cold tolerance characteristics of Korean population of potato tuber moth,Phthorimaea operculella (Zeller), (Lepidoptera: Gelechiidae)

Potato tuber moth (PTM), Phthorimaea operculella (Zeller), (Lepidoptera: Gelechiidae) is an invasive insect pest damaging solanaceous crops. We measured the supercooling point (SCP) and survival at low temperature of different development stages to determine which would be capable of overwintering in the Korean climate and adapting to low temperatures. The SCP ranges from ?23.8°C of the egg to ?16.8 of fourth instar larvae (L4). After short periods of low temperature acclimation in L3 (third instar larva), L4 and prepupae, only the prepupal stage showed a significant lowered SCP from ?20.78 to ?22.37°C. When exposed to different subzero temperature for two hours the egg turned out to be the most cold tolerant stage showing LT₅₀ of ?21.7°C followed by the pupal stage with ?15.89°C. One hundred percent mortality was observed when the larvae or adults were exposed to temperatures below ?15.1°C even for a period as short as 2 h. The results suggest that PTM pupae and egg would be the main overwintering stage in Korea where winter temperature does not drop below ?15°C.     

Comparison of the cold hardiness of two larval Lepidoptera (Noctuidae)

Abstract Diapause larvae of the European corn borer (Ostrinia nubilalis (Hubn.)) and the related Mediterranean noctuid Sesamia cretica Led. possess sufficient supercooling ability to avoid freezing over their normal environmental temperature ranges. In progressive chilling experiments (10 days acclimation at each 5° step in the temperature range from 15 to ?5°C), mean supercooling points (measured at a cooling rate of 0.1°C min^?1) were lowered from ?20.4°C at 15°C to ?24.0°C at 5°C (lower lethal temperatures: c.?28°C) in O.nubilalis, compared with ?15.0 to ?17.2°C (lower lethal temperatures: ?15 to ?17°C respectively) in S.cretica. Concentrations of glycerol and trehalose determined by gas chromatography of whole body extracts were consistently higher in the former than in the latter species at both 15 and 5°C, and may be responsible for the deeper supercooling in O.nubilalis larvae. Acclimation to 5°C increased glycerol levels in O. nubilalis extracts compared with 15°C, and this was enhanced in larvae exposed for a further 10 days at each of 0 and ?5°C (glycerol being 438μmol ml^?1 body water). Haemolymph glycerol concentrations showed a similar pattern to whole body extracts in this species. Fat body glycogen was reduced during low temperature acclimation in both species. Body water contents did not change with acclimation in O.nubilalis, whilst S.cretica, containing significantly more water, lost c.7% during acclimation from 15 to 5°C. Haemolymph osmolalities increased during acclimation, especially in Ostrinia larvae, probably as a result of the accumulation of cryoprotectants. The majority of O.nubilalis larvae survived freezing under the conditions of the cooling experiments, whilst larvae of S.cretica did not, thereby confirming an element of freezing tolerance in the former.     

Comparative assessment of the thermal tolerance of spotted stemborer,Chilo partellus (Lepidoptera: Crambidae) and its larval parasitoid,Cotesia sesamiae (Hymenoptera: Braconidae)

Under stressful thermal environments, insects adjust their behavior and physiology to maintain key life‐history activities and improve survival. For interacting species, mutual or antagonistic, thermal stress may affect the participants in differing ways, which may then affect the outcome of the ecological relationship. In agroecosystems, this may be the fate of relationships between insect pests and their antagonistic parasitoids under acute and chronic thermal variability. Against this background, we investigated the thermal tolerance of different developmental stages of Chilo partellus Swinhoe (Lepidoptera: Crambidae) and its larval parasitoid, Cotesia sesamiae Cameron (Hymenoptera: Braconidae) using both dynamic and static protocols. When exposed for 2 h to a static temperature, lower lethal temperatures ranged from ?9 to 6 °C, ?14 to ?2 °C, and ?1 to 4 °C while upper lethal temperatures ranged from 37 to 48 °C, 41 to 49 °C, and 36 to 39 °C for C. partellus eggs, larvae, and C. sesamiae adults, respectively. Faster heating rates improved critical thermal maxima (CT_max) in C. partellus larvae and adult C. partellus and C. sesamiae. Lower cooling rates improved critical thermal minima (CT_min) in C. partellus and C. sesamiae adults while compromising CT_min in C. partellus larvae. The mean supercooling points (SCPs) for C. partellus larvae, pupae, and adults were ?11.82 ± 1.78, ?10.43 ± 1.73 and ?15.75 ± 2.47, respectively. Heat knock‐down time (HKDT) and chill‐coma recovery time (CCRT) varied significantly between C. partellus larvae and adults. Larvae had higher HKDT than adults, while the latter recovered significantly faster following chill‐coma. Current results suggest developmental stage differences in C. partellus thermal tolerance (with respect to lethal temperatures and critical thermal limits) and a compromised temperature tolerance of parasitoid C. sesamiae relative to its host, suggesting potential asynchrony between host–parasitoid population phenology and consequently biocontrol efficacy under global change. These results have broad implications to biological pest management insect–natural enemy interactions under rapidly changing thermal environments.     

The effect of temperature on larval pre-settlement duration and metamorphosis for the sponge, <Emphasis Type="Italic">Rhopaloeides odorabile</Emphasis>

Rising sea temperatures may potentially affect the dispersive larval phase of sessile marine invertebrates with consequences for the viability of adult populations. This study demonstrated that the planktonic larvae of Rhopaloeides odorabile, a common Great Barrier Reef sponge, survived and metamorphosed when exposed to temperatures up to 9°C above the annual maximum (~29°C). Planktonic larval duration of 54 h, at ambient temperatures (~28°C), were reduced to 18 h for larvae exposed to elevated temperatures (32–36°C). Moreover, at ambient temperatures larvae began metamorphosing after 12 h, but at 32–36°C this reduced to only 2 h. Larvae survived and could still metamorphose at temperatures as high as 38°C, but were no longer functional at 40°C. These results imply that predicted increases in sea surface temperature may reduce planktonic larval duration and dispersal capabilities, thereby contributing to population subdivision of the species.     

Physiological flexibility: the key to success and survival for Antarctic fairy shrimps in highly fluctuating extreme environments

1. The anostracan fairy shrimp Branchinecta gaini inhabits one of the most hostile environments on earth, living in pools and lakes in Antarctica. Between January 2002 and January 2003 temperatures in two pools where B. gaini are extremely abundant on Adelaide Island ranged from ?18.6 to ?15.7 °C in winter, to 19.4 to 17.1 °C in summer, whilst air temperatures ranged from ?34 to 6.3 °C. 2. Branchinecta gaini survives winter as cysts, but endures large summer temperature fluctuations as adults. Cysts froze between ?24.4 and ?25.7 °C. In experiments adults survived 0–10 °C with no mortality for 1 week, 25 °C for nearly 48 h with 50% mortality, and at 32 °C complete mortality occurred in <1 h. 3. Oxygen consumption (M?O₂) in B. gaini approximately doubled for every 10 °C temperature rise (Q₁₀ = 2.04) up to 20 °C where it reached a peak. Females had, on average 19% higher M?O₂ than males. Females also had greater metabolic scopes, (maximum–minimum M?O₂ across temperatures was ×3.6 for females, ×3.1 for males). 4. Ventilation frequency increased linearly with temperature, and did not decline at 25 °C, indicating animals were ‘trying’ progressively harder to supply oxygen to tissues, and oxygen deficiency was the probable cause of death. Females had a higher ventilation frequency than males (8.6–17.1% higher) and they also exhibited greater scope to raise ventilation frequency (×2.4 for females versus ×1.5 for males). 5. Great metabolic flexibility allows B. gaini to exploit extreme, highly fluctuating environments, and larger ventilatory and respiratory scopes allow females to survive higher temperatures than males. Because of this flexibility their prospects for coping with physical environmental change are high.     

To eat or get heat: Behavioral trade‐offs between thermoregulation and feeding in gregarious necrophagous larvae

The thermoregulation behavior of Lucilia sericata larvae (Diptera: Calliphoridae), a necrophagous species that feeds on vertebrate cadavers, was investigated. These larvae require high heat incomes to develop, and can elevate temperatures by forming large aggregates. We hypothesized that L. sericata larvae should continue to feed at temperatures up to 38 °C, which can be reached inside larval masses. Thermal regulation behavior such as movement between a hot food spot and colder areas was also postulated. The hypotheses were tested by tracking for 1 h the activity of single, starved third instar larvae in a Petri dish containing 1 food spot (FS) that was heated to a constant temperature of 25 °C, 34 °C or 38 °C with an ambient temperature of 25 °C. The influence of previous conspecific activity in the food on larval behavior was also tested. The crops of larvae were dissected to monitor food content in the digestive systems. Based on relative crop measurements, larvae fed at all food temperatures, but temperature strongly affected larval behavior and kinematics. The total time spent by larvae in FS and the duration of each stay decreased at high FS temperature. Previous activity of conspecifics in the food slightly increased the time spent by larvae in FS and also decreased the average distance to FS. Therefore, necrophagous L. sericata larvae likely thermoregulate during normal feeding activities by adjusting to local fluctuations in temperature, particularly inside maggot masses. By maintaining a steady internal body temperature, larvae likely reduce their development time.     

Activity patterns ofChironomus yoshimatsui (Diptera: Chironomidae)

The activity patterns ofChironomus yoshimatsui were investigated experimentally to clarify whether temperature conditions experienced by the larvae and adults had an effect on the timing of adult activities. It was observed that when both larvae and adults were reared at a low temperature of 13°C, the peak of adult evening activities appeared just before simulated nightfall whereas when larvae and/or adults were reared at a high temperature of 23°C, the peak of activities occurred just after simulated night-fall. These results agreed well with field observations of seasonal changes in the timing of evening swarming and mating of this insect. The mechanism of regulating the timing of activities in accordance with temperature conditions is also discussed.     

Cold stored ectoparasitoid of Cydia fruit moths released under different temperature regimes

Cold storage of parasitoids to be used in biological control programs is desirable but risky for the performance of the stored parental generation as well as for its offspring. We studied the performance of cold stored and unstored parasitoids after release at different temperature regimes in the laboratory at the level of two subsequent generations in Hyssopus pallidus (Askew) (Hymenoptera: Eulophidae). This gregarious ectoparasitoid is a candidate biocontrol agent of Cydia pomonella L. (Lepidoptera: Tortricidae) and Cydia molesta (Busck) (Lepidoptera: Tortricidae) larvae, two fruit pests of high economic significance in apple cultivation. Cold storage for 14 days at 4°C imposed to the pupal stage of the parasitoid did not reduce the parasitism capacity of the parental generation, nor did it alter the female biased sex ratio of the progeny. Remarkably, this short-term storage of the parental generation exhibited a significant and consistently positive effect on offspring weight throughout all ambient temperature regimes, resulting in an increased offspring weight. Furthermore, offspring number was only reduced after release at low ambient temperatures, but not at 25°C and 30°C. Irrespective of whether the parasitoids originated from the stored or unstored group, highest parasitism rate was achieved at temperatures above 20°C. In conclusion, this candidate biocontrol agent can be cold stored for short periods without any measurable quality loss after release at most except at low ambient temperatures. Our findings suggest that H. pallidus is a thermophilous parasitoid that will perform best when applied at warm ambient temperatures in fruit orchards.     

Thermoregulation of termite mounds: what role does ambient temperature and metabolism of the colony play?

Summary: Termites are well known for their ability to regulate the environment of their nest such as temperature and humidity. The influence of fluctuating ambient temperature and mound characteristics on mean nest temperature and daily fluctuation of nest temperature was analysed quantitatively in the fungus-cultivating, mound-building termite Macrotermes bellicosus (Macrotermitinae) in the savanna of the Comoé National Park (Côte d'Ivoire). Additionally, the nest temperatures of inhabited and uninhabited mounds were compared to analyse the contribution of ambient temperature to nest temperature in relation to metabolic heat production of the termites and their fungi. Mound structure alone resulted in a relatively constant nest temperature. Abiotic heat production via solar radiation alone yielded nest temperatures that corresponded to mean ambient temperatures. However, only the production of metabolic heat by the termites and the fungi increased these temperatures to the actual nest temperature. Therefore, and due to the high heat capacities of the mounds, large colonies (mound height above 2.0 m) had higher nest temperatures than smaller ones. Only large colonies attain constant nest temperatures of 30 °C that are largely independent from ambient temperatures and optimal for the growth and development of the termites and their fungi.     

Sand and nest temperatures and an estimate of hatchling sex ratio from the Heron Island green turtle (Chelonia mydas) rookery, Southern Great Barrier Reef

Sand and nest temperatures were monitored during the 2002–2003 nesting season of the green turtle, Chelonia mydas, at Heron Island, Great Barrier Reef, Australia. Sand temperatures increased from ∼ 24°C early in the season to 27–29°C in the middle, before decreasing again. Beach orientation affected sand temperature at nest depth throughout the season; the north facing beach remained 0.7°C warmer than the east, which was 0.9°C warmer than the south, but monitored nest temperatures were similar across all beaches. Sand temperature at 100 cm depth was cooler than at 40 cm early in the season, but this reversed at the end. Nest temperatures increased 2–4°C above sand temperatures during the later half of incubation due to metabolic heating. Hatchling sex ratio inferred from nest temperature profiles indicated a strong female bias.     

Strategies of freeze avoidance in larvae of the goldenrod gall moth,Epiblema scudderiana: Laboratory investigations of temperature cues in the regulation of cold hardiness

Laboratory manipulations of ambient temperature were used to investigate the role of temperature in triggering or modulating cold-hardiness adaptations, supercooling-point depression and cryoprotectant accumulation, in larvae of the goldenrod gall moth, Epiblema scudderiana (Clemens), a freeze-intolerant species. Low temperature strongly facilitated cryoprotectant synthesis; larvae subjected to a 1°C per day decrease in temperature showed a major increase in the rate of glycerol synthesis when temperature fell below 5°C with highest rates of synthesis, greater than 90 μmol g⁻¹ d⁻¹, at temperatures between 0 and −10°C. Conversely, abrupt rewarming of larvae from −18 to 23°C in mid-November stimulated a rapid loss of glycerol (from a starting level of 1763 ± 278 μmol/g wet weight) with a half time of only 1.5 days. Supercooling-point depression was not keyed to ambient temperature but appeared to be an endogenous event occurring over the same time interval in laboratory animals held at warm or cold temperatures, as well as in outdoor animals. Rewarming of cold-adapted larvae in November resulted in only a small rise in supercooling point (and did not break diapause) but rewarming in February resulted in a 19°C increase in supercooling point in 4 days, followed rapidly by pupation.     

Assessing the effects of low temperature on the establishment potential in Britain of the non-native biological control agent Eretmocerus eremicus

Abstract. Eretmocerus eremicus is a parasitoid wasp that is not native to Britain. It is a biological control agent of glasshouse whitefly and has recently been released under licence in Britain for the first time. This study assessed the effect of low temperature on the outdoor establishment potential of E. eremicus in Britain. The developmental threshold calculated by three linear methods was between 6.1° and 11.6 °C, with a degree‐day requirement per generation between 256.3 and 366.8° day^?1. The supercooling points of non‐acclimated and acclimated larvae were similar (approximately ?25 °C). Non‐acclimated and acclimated larvae were subject to considerable pre‐freeze mortality, with lethal temperature (LTemp₅₀₎ values of ?16.3 and ?21.3 °C, respectively. Lethal time experiments indicated a similar lack of cold tolerance with 50% mortality of both non‐acclimated and acclimated larvae after 7 days at ?5 °C, 10 days at 0 °C and 13 days at 5 °C. Field trials showed that neither non‐acclimated nor acclimated larvae survived longer than 1 month when exposed to naturally fluctuating winter temperatures. These results suggest that releasing E. eremicus into British greenhouses would pose minimal risk because typical British winter temperatures would be an effective barrier against establishment in the wild.     

THE SOCIABLE WEAVER,PART 2: NEST ARCHITECTURE AND SOCIAL ORGANIZATION

Maclean, G. L. 1973. The Sociable Weaver, Part 2: Nest architecture and social organization. Ostrich 44:191-218.

Sociable Weavers build nest masses in a number of indigenous tree species (especially on Acacia giraffae branches) and on artificial nest sites like telephone poles. They never build in exotic trees. Nest masses are built of grass straws and roofed over with a superstructure of coarser material such as thorn twigs. The grass substructure contains the nest chambers which do not interconnect. The substructure may be divisible into two or more levels, each forming a social unit comprising the birds inhabiting it.

Each social level of birds is confined to its own structural level at all times, but a bird may roost in any chamber within its own level. The superstructure is not divisible into social units and any bird may build or perch on any part of the superstructure. Movements of birds from one colony to another are rare. The colony at one nest mass leaves the nest at about sunrise in summer, a little later in winter, and flies to the feeding grounds; the birds return to the nest mass for a siesta lasting from about 10:00 hours to 14:00 hours in hot weather, less than this in cool weather. They depart again for their feeding grounds until about sunset.

The internal temperature and RH of the nest chambers were not found to be significantly different from ambient temperature and RH when ambient temperatures were > 21,7°C. At ambient temperatures < 26,7°C the RH of the nest chambers was significantly lower than ambient Rh, but temperatures were not significantly different during the day.     

Factors governing the induction of diapause in Ephestia elutella and Plodia interpunctella (Lepidoptera)

Diapause in fully grown larvae of Ephestia elutella and Plodia inferpunctella was induced by low temperature and short photoperiods. Light intensities below 1 lx affected the induction of diapause in both species. At 20 and 25d?C, the critical photo-period for E.elutella was c. 14 h, and for P.interpunctella c. 13 h. The sensitive phase in both species occurred at about the time of the fourth larval moult. In E.elutella about seven short photoperiods were required for larvae to enter diapause. In P.interpunctella high population density during larval development increased the proportion of larvae entering diapause. The conditions inducing diapause in laboratory stocks, and in stocks collected from the field, were different. Laboratory stocks of both species did not enter diapause at 25d?C and required short photoperiods for diapause at 20d?C. Some larvae of the field stock of E.elutella entered diapause in constant darkness at 30d?C, the number being increased at low R.H., and almost all did in short photoperiods at 25°C. At 20T, most larvae of this stock entered diapause regardless of photoperiod, and at 15°C all did. In P.interpunctella up to one-third of larvae of the field stock entered diapause in short photoperiods at 25d?C, and all did if transferred to short photoperiods at 20d?C. In unheated premises, falling temperatures normally induce diapause in E.elutella each autumn, photoperiod only being important if temperatures are high. In P.interpunctella, photoperiod is a more important factor because it can override the effect of falling temperature to a greater extent than in E.elutella. In both species, however, different field populations may respond in different ways.     

Torpor patterns in the pouched mouse (Saccostomus campestris ; Rodentia): a model animal for unpredictable environments

Patterns of spontaneous and induced daily torpor were measured in the Afrotropical pouched mouse (77–115?g), Saccostomus campestris, in response to photoperiod, temperature, and food deprivation, using temperature telemetry. Photoperiod had no influence on the incidence, depth, or duration of daily torpor in either males and females. Although the testis size index decreased in response to food deprivation and photoperiod by a maximum of 24%, full testis regression did not occur. Torpor bout duration was, on average, 5.3?h, independent of photoperiod and ambient temperature. Males did not enter torpor in response to food deprivation but did in response to low ambient temperature, though significantly less frequently than females. At normothermia, the body temperatures (daily minimum, mean, maximum) of males were significantly lower than those of females. Minimum body temperatures of both males and females during torpor did not fall below 20?°C at an ambient temperature of 15?°C. The patterns of torpor measured here differ from those observed in species from strongly seasonal environments. They suggest adaptation to an environment rendered unpredictable by the El Niño Southern Oscillations. As an aseasonal, opportunistic breeder capable of year-round adaptive hypothermia, the pouched mouse represents an excellent model animal for research on physiological and behavioral adaptations to unpredictable environments.