Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m⁻² s⁻¹ PAR at each applied temperature. The photoadaptation parameter (I _k) and the maximum photosynthetic rate (P _max) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low I _k at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m⁻² s⁻¹. At lower irradiance levels (7.5–30 μmol m⁻² s⁻¹), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species.     

Thermal biology and establishment potential in temperate climates of the aphid parasitoid, <Emphasis Type="Italic">Lysiphlebus testaceipes</Emphasis>

Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae) is a parasitic wasp which plays an important role in the biological control of a number of aphid species. Through assessment of its thermal biology and low temperature tolerance, this study ascertains the establishment potential of L. testaceipes in cool temperate climates typical of northern Europe. The developmental threshold of L. testaceipes was 5.8°C. Rearing of parasitoids at shorter day lengths and lower temperatures indicated no ability to enter a diapause state. The supercooling points (SCP) of non-acclimated and acclimated parasitoid life stages were between −24.6°C and −17.7°C, with LTemp₅₀ temperatures approaching these values, indicating a high level of cold tolerance in short exposures. At 5°C the LTime₅₀ of acclimated larvae within parasitized aphids was 42.8 days. Acclimated pupae continued to develop with 54% adult emergence from mummies within 60 days. Acclimated parasitoid larvae and pupae, within living and mummified aphids, continued to develop during 70 days of winter field exposure and emerging adult parasitoids were reproductively viable under field conditions. These data indicate that where suitable host species are available throughout the year, L. testaceipes would be able to establish in northern Europe.     

Establishment potential of the predatory mirid <Emphasis Type="Italic">Dicyphus hesperus</Emphasis> in northern Europe

The predatory mirid Dicyphus hesperus Knight (Hemiptera: Miridae) is native to North America. The species has been used for the control of glasshouse whitefly on aubergine in the Netherlands, and is currently being evaluated for continued and wider release in Europe. Field and laboratory studies were conducted on a population collected from southern California, USA, to assess the cold tolerance and potential for outdoor establishment under prevailing northern European climates. The supercooling points (whole animal freezing temperatures) of nymphal and adult insects were around −20°C. The lethal temperatures (LTemp₅₀) of non-diapausing nymphs and adults and diapausing adults were close to their respective freezing temperatures at −17.6, −17.6 and −19.2°C. At 5°C, the LTime₅₀ was 54, 101.7 and 117.5 days for fed nymphs, non-diapausing and diapausing adults respectively. When first instar nymphs were placed in the field in winter, starved samples died out after 70 days, but 5% of the fed nymphs survived until the end of winter (140 days) and developed to adult on return to the laboratory. After a similar 5-month field exposure, 50% of fed diapausing adults and 15% of fed non-diapausing adults were still alive at the end of winter, whereas starved diapausing adults died after 140 days. On return to the laboratory after 5 months in the field, both diapausing and non-diapausing adults mated and laid eggs, forming viable populations. Overall, the field and laboratory experiments indicate that this population of D. hesperus is able to enter diapause and that winter temperatures are not a barrier to establishment in northern Europe.     

Heat tolerance of developmental and seasonal stages of Chilo suppressalis

Global warming means that the ability to withstand heat stress is of crucial importance to insects' survival and reproduction. Insects have various ways of achieving thermal tolerance, which can be affected by thermal history, physiological state, and seasonal cycles. In this study, we compared the thermal tolerance of life stages and seasons of a wild population of the striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), an economically significant pest of rice crops in Asia. Our results demonstrate that the eggs, larvae, and adults of C. suppressalis collected in rice fields in Yangzhou, China, are able to tolerate extremely high temperatures, in excess of those this species encounters in nature. We found that egg masses had a survival rate of 75% after being kept at 42 °C for 8 h. Egg masses exposed to 39 °C for 8 h had the longest hatching time (3.3 days). LTemp₅₀ and LTemp₉₀ (i.e., the temperatures at which 50 or 90% of individuals died within 2 h) of larvae collected in late summer were 45.4 and 47.3 °C, respectively. LTime₅₀ and LTime₉₀ (i.e., the time required to kill 50 or 90% of individuals) at 44 °C were 6.2 and 9.6 h, respectively. The corresponding values for 46 °C were 1.5 and 2.6 h. We also found that the heat tolerance of adults collected in late summer was lower than that of larvae. For example, LTemp₅₀ of male and female adults was 43.8 and 43.6 °C, respectively. Other measures of the heat tolerance of adults, such as LTime₅₀ at 42 °C, also differed between the sexes, being 5.9 h for males and 7.2 h for females. Although adult survival was robust to heat stress, adult fertility was more sensitive. Our results also indicate that although the second generation of adults (i.e., the summer generation) typically encountered higher temperatures than the overwintering generation, survival of the second generation adults was lower.     

Thermal biology and establishment potential in temperate climates of the predatory mirid <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis>

Nesidiocoris tenuis Reuter (Hemiptera: Miridae) is a polyphagous mirid currently used for the control of leafminers, thrips, whitefly and spider mites in Mediterranean regions to which it is indigenous. This study investigates the establishment potential of N. tenuis in cool temperate climates typical of northern Europe through assessment of its thermal biology and low temperature tolerance in laboratory and field experiments. The developmental threshold of N. tenuis was estimated to be 12.9°C with no indication of ability to diapause. Supercooling points of the acclimated and non-acclimated adults and nymphs of the mirid were between −17.6° and −21.5°C and the LTemp₅₀ was around −12°C, indicating a high level of pre-freeze mortality. The LTime₅₀ at 5°C was nine days and 100% mortality occurred after less than four weeks of winter field exposure. Collectively these data suggest that N. tenuis is unlikely to establish in northern Europe and would therefore have little or no non-target effects on native species in such regions.     

Temperature-dependent development and reproductive traits of <Emphasis Type="Italic">Tetranychus macfarlanei</Emphasis> (Acari: Tetranychidae)

Development and reproductive traits of Tetranychus macfarlanei Baker & Pritchard (Acari: Tetranychidae) were investigated on kidney bean, Phaseolus vulgaris L., at eleven constant temperatures. Tetranychus macfarlanei was able to develop and complete its life cycle at temperatures ranging from 17.5 to 37.5°C. At 15 and 40°C, a few eggs (2–4%) hatched but further development was arrested. Development from egg to adult was slowest at 17.5°C and fastest at 35°C for both females and males. Using Ikemoto and Takai’s linear model, the estimated lower developmental thresholds for egg-to-female adult, egg-to-male adult and egg-to-egg development were 12.9–13.0°C. The thermal constants for the respective stages were 110.85, 115.99 and 125.32 degree-days (DD). The intrinsic optimum temperatures (T _Φ) calculated by non-linear SSI model were determined as 24.4, 24.4 and 24.2°C for egg-to-female adult, egg-to-male adult and egg-to-egg development, respectively. The net reproductive rate (R ₀) was highest at 25°C (167.4 females per female) and lowest at 17.5°C (42.6 females per female). The intrinsic rate of natural increase, r _m, increased linearly with the rising of temperature from 0.102 at 17.5°C to 0.441 day⁻¹ at 35°C. These values suggested that T. macfarlanei could be growing quickly in response to increasing temperatures from 17.5 to 35°C and provide a basis for predicting its potential geographical range.     

Exponential growth of “snow molds” at sub-zero temperatures: an explanation for high beneath-snow respiration rates and Q 10 values

Numerous studies have demonstrated exceptionally high temperature sensitivity of the beneath-snow respiratory flux in cold-winter ecosystems. The most common, but still untested, explanation for this high sensitivity is a physical one based on the observation that water availability in soils increases exponentially as soils warm from −3 to 0°C. Here, we present evidence for a biological hypothesis to explain exponential kinetics and high Q ₁₀ values as beneath-snow soils warm from −3 to 0°C during the early spring in a high-elevation subalpine forest. First, we show that some of the dominant organisms of the beneath-snow microbial community, “snow molds”, exhibit robust exponential growth at temperatures from −3 to −0.3°C. Second, Q ₁₀ values based on growth rates across the temperature range of −2 to −0.3°C for these snow molds vary from 22 to 330. Third, we derive an analytical equation that combines the relative contributions of microbial growth and microbial metabolism to the temperature sensitivity of respiration. Finally, we use this equation to show that with only moderate snow mold growth (several generations), the combined sensitivities of growth and metabolism to small changes in beneath-snow soil temperature, create a double exponential in the Q ₁₀ function that may explain the extremely high (~1 × 10⁶) Q ₁₀ values observed in past studies. Our biological explanation for high Q ₁₀ levels is supported by several independent studies that have demonstrated build up of microbial biomass under the snow as temperatures warm from −2 to 0°C.     

The influence of snowfall,temperature and social relationships on sleeping clusters of Japanese monkeys during winter in Shiga Heights

We studied Japanese monkeys (Macaca fuscata) of the Shiga A₁ troop at their sleeping sites in Shiga Heights, Japan, for 41 nights during 3 winters. Monkeys chose their sleeping sites in Japanese cedars and in deciduous broad-leaved forests on non-snowing nights and in Japanese cedar forests on snowing nights. We counted 399 sleeping clusters in which 2 or more monkeys remained in physical contact through the night and 43 solitary sleeping monkeys, though monkeys did not maintain physical contact with others in the daytime. We found 397 clusters on tree branches and 2 clusters on rocks. The mean size of huddling clusters was 3.06±1.22 SD. The cluster size (3.17±1.26 SD) at lower ambient temperatures between −7 and −4°C was larger than that at higher temperatures between −2 and 4°C (cluster size 2.88±1.13 SD). Most clusters were composed of kin. Females kept close to related females in the daytime and huddled with them at night. The highest-ranking male mainly huddled with his kin and his familiar females. Other males kept farther apart from each other in the daytime, probably to avoid social conflicts. Through cold winter nights, however, such males reduced inter-individual distances and huddled with other males. Japanese monkeys appear to recognize three types of inter-individual distances: an intimate distance less than 1 m, a personal distance of 1–3 m and a social distance of 3–20 m; they change their inter-individual distances according to social and ecological circumstances.     

Thermal biology, torpor use and activity patterns of a small diurnal marsupial from a tropical desert: sexual differences

Many small desert dasyurids employ torpor almost daily during winter, because cold nights and low food availability impose high energetic costs. However, in Western Australia the arid zone extends into tropical, coastal regions, where winter temperature conditions are far less severe. We studied the thermal biology and activity patterns of free-ranging kaluta (~27 g), a dasyurid restricted to these tropical spinifex deserts, during the Austral winter (June–July) and in addition quantified activity patterns in captivity. Unlike most dasyurids, wild and captive kalutas were almost exclusively diurnal and retreated into underground burrows during the night. Despite being active during the warmer part of the day, kalutas entered torpor daily. However, torpor patterns differed remarkably between males and females. While females spent most of the night torpid at body temperatures (T _b) as low as 21°C, close to soil temperature, males entered multiple short and shallow bouts (T _b > 25°C) during the night. Males also maintained higher T _bs during the early morning when active, occupied larger home ranges and covered greater distances while foraging than females. Hence, males appear to expend more energy than the similar-sized females both while foraging and during the rest phase. We propose that physiological as well as behavioural preparations for the September mating season that culminate in a complete male die-off might already impose energetic costs on males during winter.     

Cold tolerance of the maize orange leafhopper,Cicadulina bipunctata

Cicadulina bipunctata was originally distributed in tropical and subtropical regions of the Old World. This leafhopper recently expanded its distribution area to southern parts of temperate Japan. In this study, factors affecting the overwintering ability of C. bipunctata were examined. A series of laboratory experiments revealed that cold acclimation at 15 °C for 7 days enhanced the cold tolerance of C. bipunctata to the same level as an overwintering population, adult females were more tolerant of cold temperature than adult males, and survival of acclimated adult females was highly dependent on temperature from −5 to 5 °C and exposure duration to the temperature. The temperature of crystallization of adult females was approximately −19 °C but temperatures in southern temperate Japan rarely dropped below −10 °C in the winter, indicating that overwintering C. bipunctata adults in temperate Japan are not killed by freezing injury but by indirect chilling injury caused by long-term exposure to moderately low temperatures. An overwintering generation of C. bipunctata had extremely low overwinter survival (<1%) in temperate Japan; however, based on winter temperature ranges, there are additional areas amenable to expansion of C. bipunctata in temperate Japan.     

Accumulation of lactate by supercooled hatchlings of the painted turtle (Chrysemys picta): implications for overwinter survival

Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest where they completed embryogenesis the preceding summer. Neonates at northern localities consequently may be exposed during winter to subzero temperatures and frozen soil. Hatchlings apparently survive exposure to such conditions by supercooling, but the physiological consequences of this adaptive strategy have not been examined. We measured lactate in hatchling painted turtles after exposure to each of three temperatures (0 °C, −4 °C, and −8 °C) for three time periods (5 days, 15 days, and 25 days) to determine the extent to which overwintering hatchlings might rely on anaerobic metabolism to regenerate ATP. Whole-body lactate increased with increasing duration of exposure and decreasing temperature, and the highest levels were associated with the group that experienced the highest mortality. These results indicate that animals may develop a considerable lactic acidosis during a winter in which temperatures fall below 0 °C for weeks or months and that accumulation of lactate may contribute to mortality of overwintering animals. Accepted: 20 October 1999     

Temperature Requirements may Explain why the Introduced Parasitoid Quadrastichus citrella Failed to Control Phyllocnistis citrella in Spain

Quadrastichus citrella Reina and La Salle (Hymenoptera: Eulophidae) is a parasitoid of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), indigenous to South Eastern Asia where it is considered a key natural enemy of this pest. It was introduced in Spain in a classical biological control program and became established, but was not as successful as forecast. To check whether its biology could explain this lack of control, development and reproduction at different temperatures were studied. Quadrastichus citrella can survive at temperatures between 15 and 35 °C. Lower development threshold was 12.3 °C, which resulted in a thermal constant of 138.06 DD. The combination of development and reproduction into demographic parameters resulted in highest net reproduction occurring in the range 20–25 °C (78.2 females per female), and highest intrinsic rate of increase at 30 °C (0.2571 females per female per day). These values make Q. citrella an intrinsically superior natural enemy compared to other leaf miner parasitoids. However, overwintering of Q. citrella in Spain may present a barrier, especially in areas like Valencia, where average winter temperatures are around 11 °C. This could account for the low recovery rates observed in Spain in spite of the key natural enemy status enjoyed by this species in its area of origin.     

Overwinter body temperature patterns in captive jerboas (<Emphasis Type="Italic">Jaculus orientali</Emphasis>s): influence of sex and group

The jerboa (Jaculus orientalis) has been described in the past as a hibernator, but no reliable data exist on the daily and seasonal rhythmicity of body temperature (T _b). In this study, T _b patterns were determined in different groups of jerboas (isolated males and females, castrated males and grouped animals) maintained in captivity during autumn and winter, and submitted to natural variations of light and ambient temperature (T _a). T _b and T _a variations were recorded with surgically implanted iButton temperature loggers at 30-min intervals for two consecutive years. About half (6/13) of isolated female jerboas hibernated with a T _b < 33°C, with hibernation bouts interspersed with short periods of normothermy from November to February. Hibernation bout durations were longer (4–5 days) than those of normothermia phases (1–4 days). During hibernation, the minimum T _b was low (T _bmin ~10.7°C). In contrast, one of the 12 isolated males showed short hibernation bouts of ca. 2 days late in the hibernation season, February–March. The males had T _bmin values of 15.1°C. In contrast to predictions, no castrated males hibernated. When jerboas were grouped, females and males exhibited concomitant torpor bouts. In males, the longest bouts were observed during the late hibernation season. These data suggest complex regulation of hibernation in jerboas.     

Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor

The body temperature (T _b) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal T _b of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily T _b was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (T _g) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean T _b (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase T _b of 38.1 ± 0.1°C and a mean inactive phase T _b of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of T _b rhythm was 3.8 ± 0.2°C. T _b during the active phase closely followed T _g and mean active phase T _b was significantly correlated with mean active phase T _g (r ² = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive phase T _b was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed.     

Mycelial growth of the snow mold fungus, Sclerotinia borealis, improved at low water potentials: an adaption to frozen environment

The snow mold fungus, Sclerotinia borealis, shows optimal growth at 4°C on potato dextrose agar (PDA) and can grow even at subzero temperature. Its mycelial growth was improved on frozen PDA at −1°C and on PDA containing potassium chloride (KCl) (water potential, −4.27 to −0.85 MPa) or d(−) sorbitol (−3.48 to −0.92 MPa). Its optimal growth temperature shifted from 4 to 10°C on PDA amended with KCl or sorbitol, indicating that inherent optimal growth occurs at high temperatures. These results suggest that S. borealis uses concentrated nutrients in the frozen environment and that such physiologic characteristics are critical for the fungus to prevail at subzero temperatures.     

Kinetics of lipase catalyzed isoamyl acetate synthesis at high hydrostatic pressure in hexane

Lipase-catalyzed synthesis of isoamyl acetate in hexane at 10–250 MPa at 80°C and 1–100 MPa at 40°C resulted in activation volumes of −12.9 ± 1.7 and −21.6 ± 2.9 cm³ mol⁻¹, respectively. Increasing pressure from 10 to 200 MPa resulted in approximately 10-fold increase in V _max at both 40 and 80°C. Pressure increased the K _m from 2.4 ± 0.004 to 38 ± 0.78 mM at 40°C. In contrast, at 80°C the pressure did not affect the K _m.     

Biology of Doryctobracon brasiliensis at different temperatures: development of life table and determining thermal requirements

Doryctobracon brasiliensis (Szépligeti) is a parasitoid larval–pupal of fruit flies and has great potential to be used in biological control programmes as it feeds on other Anastrepha species in addition to Anastrepha fraterculus (Wiedemann). This study investigated the biology of D. brasiliensis at different temperatures to design a life fertility table and determine thermal requirements. The parasitoids were multiplied in larvae of A. fraterculus in air‐conditioned chambers at 15, 18, 20, 22, 25, 28 and 30°C, 70 ± 20% RH and photophase of 12 h. We determined the number of offspring, sex ratio, longevity of males and females and duration of egg–adult period. The temperature range 18–22°C ensures higher fecundity and at 20°C, and the average number of offspring per female was 152.77 parasitoids. The sex ratio of offspring produced was reduced with increasing temperatures. Longevity of males and females of D. brasiliensis was reduced by increasing temperatures. At 15, 28 and 30°C, there was no development of immature stages. For the temperature range 18–25°C, the duration of egg–adult period of D. brasiliensis was inversely proportional to temperature. At 20 and 22°C, we observed the highest values of net reproduction rate (Ro) and finite reason of increase (λ), meaning that at the estimated optimum temperature (21°C), the population of D. brasiliensis increased 47 times each generation. The lower temperature threshold for development was 10.01°C and the thermal constant (K) 303.21 degree/days. This information confirms that D. brasiliensis is better suited to temperate environments, which implies a significant potential for the use of D. brasiliensis in the control of A. fraterculus, because most areas occupied by this pest are in temperate regions. In addition, D. brasiliensis is useful in mass rearing systems in laboratory.     

Temperature-dependent development and life table parameters of <Emphasis Type="Italic">Typhlodromus bagdasarjani</Emphasis> (Phytoseiidae) fed on two-spotted spider mite

The predatory mite Typhlodromus bagdasarjani Wainstein and Arutunjan (Acari: Phytoseiidae) is an indigenous and widespread species of the Middle East fauna. In this paper we assess the effect of temperature on developmental rate and reproduction potential of T. bagdasarjani under laboratory conditions. The development of this species was determined at 15, 20, 25, 30, 35 and 37.5 ± 1°C, 60 ± 10% RH and L16:D8 h photoperiod. The total developmental time averaged 28.2, 15.0, 8.9, 7.6, 7.2 and 7.4 days at 15–37.5°C, respectively, when feeding on immature stages of two-spotted spider mite, Tetranychus urticae Koch. The lower developmental threshold (T ₀ ) and thermal constant (K) for the development of this predator were estimated 9.2°C and 162 degree-days by the Ikemoto linear model. The life table parameters were estimated at 15–35°C. The shortest life span of females at 35°C was 45.0 days, followed by 50.7, 50.9, 103.3 and 136.8 days at 30, 25, 20 and 15°C, respectively. Mated females laid on average 19.9, 26.3, 41.1, 39.6 and 31.3 eggs per female at 15–35°C, respectively. The intrinsic rate of increase (r _m ) and finite rate of increase (λ) increased significantly with increasing temperature. The r _m values ranged from 0.021 (15°C) to 0.186 (35°C) days⁻¹. The highest value of net reproductive rate (R ₀) was 13.6 females progeny/female/generation at 25°C. The results demonstrated that T. bagdasarjani is well adapted to high temperatures. However, the efficiency to control spider mites may be affected by behavioral characteristics of the predator and its prey under real conditions.     

Thermal tolerance and acclimation response of larvae of the sub-Antarctic beetle Hydromedion sparsutum (Coleoptera: Perimylopidae)

Hydromedion sparsutum is a locally abundant herbivorous beetle on the sub-Antarctic island of South Georgia, often living in close association with the tussock grass Parodiochloa flabellata. Over a 4-day period in mid-summer when the air temperature varied from 0 to 20°C, the temperature in the leaf litter 5–10 cm deep at the base of tussock plants (the microhabitat of H. sparsutum) was consistently within the range of 5–7.5°C. Experiments were carried out to assess the ability of H. sparsutum larvae collected from this thermally stable environment to acclimate when maintained at lower (0°C) and higher (15°C) temperatures. The mean supercooling points (freezing temperature) of larvae collected in January and acclimated at 0°C for 3 and 6 weeks and 15°C for 3 weeks were all within the range of −2.6 to −4.6°C. Larvae in all treatment groups were freeze tolerant. Acclimation at 0°C significantly increased survival in a 15-min exposure at −8°C (from 27 to 96%) and −10°C (from 0 to 63%) compared with the field-fresh and 15°C-treated larvae. Similarly, survival of 0°C-acclimated larvae in a 72-h exposure at −6°C increased from 20 to 83%. Extending the acclimation period at 0°C to 6 weeks did not produce any further increase in cold tolerance. The concentrations of glucose and trehalose in larval body fluids increased significantly with low temperature acclimation. Larvae maintained at 15°C for 3 weeks (none survived for 6 weeks) were less able to survive 1-h exposures between 30 and 35°C than the 0°C-treated samples. Whilst vegetation and snow cover are an effective buffer against low winter temperatures in many polar insects, the inability of H. sparsutum larvae to acclimate or survive at 15°C suggests that protection against high summer temperatures is equally important for this species. Accepted: 2 August 1999     

Fluctuation in the abundance of the narrow-headed ant (<Emphasis Type="Italic">Formica exsecta</Emphasis>, hYmenoptera,Formicidae) and climatic changes in the northeastern part of its range

In some localities of the upper reaches of the Kolyma River, the narrow-headed ant (Formica exsecta Nylander, 1846) has become the dominant species instead of a rare one during the last decade. To study this phenomenon, soil temperatures at a depth of 20 cm were measured in the winter of 2008–2009, near 11 nests of this species and in 11 more biotopes without nests, in the same localities where similar measurements had been carried out in the 1980s. The growth of minimum air temperatures by 2–2.5°C combined with increased snow cover since the end of the past century by the present time, has resulted in the minimal soil temperatures at a depth of 20 cm rising by 3–7°C. Being one of the least cold-resisting species of the genus (with limit of tolerance −12…−15°C), the narrow-headed ant has responded to winter warming of soils by increasing the variety of inhabited biotopes by 3–4 times, from 5–6 to 20–23 out of more than 43 examined; its abundance has grown sharply, to 130 nests per survey route 1300 m long and 20 m wide. Within the frame of the existing climate such deviations of soil temperature may occur once every 15–20 years. Therefore the changes observed may represent regular fluctuations. The prediction of population dynamics of F. exsecta in other parts of the subarctic belt within the permafrost zone should take into account the climatic specificity of the region which may considerably differ from that in adjoining territories.