Critical thermal limits and their responses to acclimation in two sub-Antarctic spiders: <Emphasis Type="Italic">Myro kerguelenensis</Emphasis> and <Emphasis Type="Italic">Prinerigone vagans</Emphasis>

Despite the relative richness of spider species across the Southern Ocean islands remarkably little information is available on their biology. Here, the critical thermal limits of an indigenous (Myro kerguelenensis, Desidae) and an introduced (Prinerigone vagans, Linyphiidae) spider species from Marion Island were studied after 7–8 days acclimation to 0, 5, 10 and 15°C. Critical thermal minima (CT_Min) were low in these species by comparison with other spiders and insects measured to date, and ranged from −6 to −7°C in M. kerguelenensis and from −7 to −8°C in P. vagans. In contrast, critical thermal maxima (CT_Max) were similar to other insects on Marion Island (M. kerguelenensis: 35.0–35.6°C; P. vagans: 35.1–36.0°C), although significantly lower than those reported for other spider species in the literature. The magnitude of acclimation responses in CT_Max was lower than those in CT_Min for both species and this suggests decoupled responses to acclimation. Whilst not conclusive, the results raise several important considerations: that oxygen limitation of thermal tolerance needs to be more widely investigated in terrestrial species, that indigenous and alien species might differ in the nature and extent of their plasticity, and that upper and lower thermal tolerance limits might be decoupled in spiders as is the case in insects.     

Microhabitat segregation and physiological differences in co-occurring tiger beetle species,Cicindela oregona and Cicindela tranquebarica

Summary The daily movements of two co-occurring tiger beetle species were monitored in conjunction with changes in microclimate along streams in Northeast Arizona. Cicindela oregona and C. tranquebarica temporarily segregated across areas of beach exhibiting different microclimates. C. oregona progressively moved from the dry upper beach to the wet stream edge as beach temperatures increased and humidity decreased. The actively foraged throughout the day in this moist habitat at air temperatures between 25 and 38°C. C. tranquebarica remained on the dry, upper portions of the beach and shuttled between sun and shade at air temperatures above 35°C. Only when stream edge temperatures exceeded 30°C was tranquebarica found in this subhabitat. Both species exhibited physiological tolerances in the laboratory that were consistent with their microhabitat preferences in the field. Although both species had similar high lethal temperatures (47–48°C) in saturated air, oregona died at lower temperatures (39–43°C) than tranquebarica (46–47°C) under dry (0% RH) conditions. C. oregona was considerably more active than tranquebarica at body temperatures below 30°C and exhibited higher levels of active metabolism between 25 and 40°C. In addition, C. tranquebarica exhibited significantly lower water loss rates than oregona at 30, 35 and 40°C.     

Physiology of cold hardiness in cocoons of five earthworm taxa (Lumbricidae: Oligochaeta)

Earthworm cocoons are mostly found in the uppermost soil layers and are therefore often exposed to low temperatures during winter. In the present study, cocoons of five taxa of earthworms were investigated for their tolerance to freezing, melting points of cocoon fluids and dehydration of cocoons when exposed to a frozen environment. Embryos of the taxa investigated were freeze intolerant. The melting points of fully hydrated cocoon fluids were high (above –0.3°C) and thermal hysteresis factors were absent. Exposure to a frozen environment caused the cocoons to dehydrate drastically and dehydrated cocoons showed significantly lower super-cooling points than fully hydrated cocoons, reducing the risk of freezing for dehydrated cocoons. It is proposed therefore that the cold-hardiness strategy of the earthworm cocoons is based on dehydration upon exposure to subzero temperatures in the frozen environment. Cocoons of three surface-dwelling taxa, Dendrobaena octaedra, Dendrodrilus rubidus tenuis and Dendrodrilus rubidus norvegicus had lower supercooling points and survived frost exposure better than cocoons of two deeper-dwelling taxa, Aporrectodea caliginosa and Allolobophora chlorotica. One of the investigated taxa, D. r. norvegicus, was collected from a cold alpine habitat. However, it was not more cold hardy than the closely related D. r. tenuis collected from a lowland temperate habitat. D. octaedra was the most cold hardy taxon, its cocoons being able to withstand –8°C for 3 months and –13.5°C for 2 weeks in frozen soil.Abbreviations dw dry weight - fw fresh weight - SCP supercooling point     

Ventilation rate and behavioural responses of two species of intertidal goby (Pisces: Gobiidae) at extremes of environmental temperature

We investigated the behavioural responses of two gobiid fish species to temperature to determine if differences in behaviour and ventilation rate might explain any apparent vertical zonation. A survey of the shore at Manly, Moreton Bay revealed Favonigobius exquisitus to dominate the lower shore and Pseudogobius sp.4 the upper shore. These species were exposed to a range of temperatures (15–40°C) in aquaria for up to 6 h. At 20 °C F. exquisitus exhibited a mean gill ventilation rate of 26 ± 1.4 bpm (beats per minute) differing significantly from Pseudogobius, which ventilated at a fivefold greater rate of 143 ± 6 bpm. The ventilation rate in F. exquisitus underwent a fivefold increase from normal local water temperature (20 °C) to high temperature (35 °C) conditions, whereas that of Pseudogobius did not even double, suggesting that Pseudogobius sp. is a better thermal regulator than F. exquisitus.While both species emerged from the water at high temperatures (>30 °C) the behaviours they exhibited while immersed at high temperature were quite different. F. exquisitus undertook vertical displacement movements we interpret as an avoidance response, whereas Pseudogobius sp. appeared to use a coping strategy involving movements that might renew the water mass adjacent to its body. The thermal tolerances and behaviours of F. exquisitus and Pseudogobius sp. are in broad agreement with their vertical distribution on the shore.     

Physiological tolerances of juvenile robust redhorse, Moxostoma robustum: conservation implications for an imperiled species

The robust redhorse, Moxostoma robustum (Teleostei: Catostomidae), is an imperiled sucker native to large rivers of the Atlantic slope of the southeastern United States. Juvenile M. robustum were tested for tolerances to temperature, salinity, pH, and hypoxia in order to evaluate basic early life-history requirements. Static (acute) tests resulted in estimates of mean lower temperature tolerances (5.3–19.4 °C) that varied with prior thermal acclimation and indicated no apparent difference in tolerance among fish 30, 60, and 90 days old. Fish acclimated to 20 °C and 30 °C had significantly different mean critical thermal maxima (34.9 °C and 37.2 °C, respectively) and exhibited pronounced increased opercular ventilation rates with elevated temperatures. Fish exposed to acute and chronic increases in salinity showed unusual patterns of mortality above the isosmotic point (9 ppt) that reflected possible differences in body mass and prior acclimation conditions (i.e., water ionic composition); small fish and those held in soft water were the least tolerant of increased salinity. Abrupt exposure to extreme pH values resulted in greater than 50% mortality at pH values below 4.3 and above 9.5 within a 96-hour period. Fish exposed to progressive hypoxia utilized aquatic surface respiration at a mean oxygen concentration of 0.72–0.80 mg O₂ l^-1 (20 °C and 30 °C acclimated fish, respectively), and lost equilibrium at 0.54–0.57 mg O₂ l^-1. Juvenile M. robustum are moderately tolerant of a wide range of ambient physicochemical parameters, but further research is needed to determine how both abiotic and biotic factors have contributed to population decline and extirpation of this species.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

A quantitative scuba-diving survey of the sublittoral macrobenthos at subantarctic Marion Island

Summary A SCUBA-diving survey of the macrobenthos of hard substrata in the sublittoral zone at subantarctic Marion Island was conducted during March and April 1988. Dense beds (12 kg m^–2) of the kelp Macrocystis laevis occur in depths > 5 m. Durvillaea antarctica is found along the infralittoral fringe and Desmarestia rossi and Durvillaea sp. occur in a narrow zone from 3 m–6 m. Under-storey algae (chiefly rhodophytes) tend to decrease in biomass with depth, with mean values of 1.57 kg m^–2 at 5m, 0.75 kg m^–2 at 10m and 0.49 kg m^–2 at 15 m. Encrusting coralline algae are particularly abundant in shallow areas (¯x = 0.92 kg m^–2) but are insignificant in deeper areas. Total biomass of macrozoobenthos increased with depth with mean values of 0.12 kg m^–2 at 5 m, 0.34 kg m^–2 at 10 m and 0.46 kg m^–2 at 15 m. Polychaetes, crustaceans, echinoderms, molluscs, sponges and bryozoans dominated the macrozoobenthos in terms of biomass. Approximately 200 species of macrobenthic animals were recorded and numerically, polychaetes, crustaceans, molluscs, nematodes and echinoderms dominated. The sublittoral benthos at Marion Island is compared with that occurring at other subantarctic and Antarctic islands, in particular, the Kerguelen Island group. Zoogeographic trends and the possible effects of nutrient input from seabird guano are briefly discussed.     

Aspects of the thermal ecology of the rusty crayfish Orconectes rusticus (Girard)

Summary Orconectes rusticus currently is undergoing an explosive range expansion in the midwestern U.S.A., but information on the potentially important effects of water temperature on the species' biology is lacking. The thermal ecology of O. rusticus in southwestern Ohio, U.S.A., was examined by determining 1) the effects of four water temperatures (16, 20, 25, and 29°C) on survival and growth of juveniles, 2) the responses of juveniles and adults to a thermal gradient (7–27° C), and 3) the thermal tolerances (critical thermal maximum, CTMax, and critical thermal minimum, CTMin) of free-living, field-acclimatized juveniles and adults on a biweekly basis throughout the summer. Month-long growth experiments predicted maximum growth rates of juveniles at water temperatures between 26 and 28°C, but greatest survival between 20 and 22° C. Laboratory-acclimated (22° C) adults and field-acclimatized (2.5° C) juveniles both had an acute preferred temperature of 22° C. CTMaxs and CTMins of juveniles were 0.5–2.6° C higher than those of adults throughout the summer, suggesting that juveniles were exposed to water temperatures 1.5–6.8° C warmer than those of adults. Juvenile and adult O. rusticus prefer habitats where water temperatures favor maximum survival, but they usually are not found together in the same habitat; adults apparently displace the juveniles into warmer habitats. Warmer temperatures can decrease survival of juveniles but improve their growth rates, leading to enhanced fecundity and competitive ability. The past and future success of O. rusticus in expanding its range may depend, in part, on the species ability to adjust to new thermal environments occupied by other species of crayfish.     

Climate change and the short-term impact of feral house mice at the sub-Antarctic Prince Edward Islands

At the Prince Edward Islands, temperatures have increased by approximately 1°C over the past 40 years, accompanied by a decline in precipitation. This has led to a reduction in the peat moisture content of mires and higher growing season warmth. The temperature-and moisture-sensitive sedge, Uncinia compacta R. Br. (Cyperaceae), has consequently increased its aerial cover on Prince Edward Island, but harvesting of seeds by feral house mice (up to 100% removed) has prevented this from happening on Marion Island. Such extensive use of resources suggests that prey switching may be taking place at Marion Island. Scat analyses revealed that mice are·not only eating ectemnorhinine weevils to a greater extent than found in previous studies of populations at Marion Island, but that they also prefer larger weevils (±6 mm). A decrease in body size of preferred weevil prey species [Bothrometopus randi Jeannel and Ectemnorhinus similis C.O. Waterhouse (Coleoptera: Curculionidae)] has taken place on Marion Island (1986–1992), but not on Prince Edward Island. This appears to be a result of increased predation on weevils. In addition, adults of the prey species, E. similis are relatively more abundant on Prince Edward Island than adults of the smaller congener E. marioni Jeannel, and could not be found on Marion Island in the late austral summer of 1991. These results not only provide support for previous hypotheses of the effect of global warming on mouse-plant-invertebrate interactions on the Prince Edward Islands, but also provide limited evidence for the first recorded case of predator-mediated speciation. They also show that the interaction of human-induced changes operating at different scales may have profound consequences for local systems.     

Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae)

The cold-hardiness of Dermacentor marginatus using laboratory-reared offspring of ticks collected in Germany was characterized. Investigations of unfed stages revealed that adult ticks suffered 50% mortality at –10°C after 4–5 months, but larvae and nymphs suffered mortality within few days, whereas –15°C was lethal for all stages within a very short period. Larval hatch and moulting of engorged larvae and nymphs did not occur at 10°C. Embryonic development of eggs with larval hatch was considerably reduced by exposure of eggs to 10°C. Engorged females did not lay eggs at 10°C, the oviposition capability, however, persisted over 6 months at 10°C, 5 months at 5°C, 3 months at 0°C and 2 months at –10°C without substantial decrease of the oviposition capacity or reduction of viable eggs. These results present evidence that unfed adult ticks are the ecoepidemiologically most effective stages, which are capable to tolerate long and extremely cold winters without substantial impairment of the population density. It is also considered that engorged females interrupt their oviposition at low and subzero temperatures delaying it for months and so contribute in bypassing winter conditions. None of the stages survived supercooling indicating that D. marginatus is freeze intolerant. Mean supercooling point (SCP) ranged between –26°C in eggs and –12, 6°C in engorged females. Compared with eggs, the SCP of the other stages was significantly higher. In conclusion, the SCP is considered to have no predictive value in the context with cold-hardiness.     

Cold tolerance of Littorinidae from southern Africa: intertidal snails are not constrained to freeze tolerance

All intertidal gastropods for which cold tolerance strategies have been assessed have been shown to be freeze tolerant. Thus, freeze tolerance is considered an adaptation to the intertidal environment. We investigated the cold tolerance strategies of three species of subtropical and temperate snails (Gastropoda: Littorinidae) to determine whether this group is phylogenetically constrained to freeze tolerance. We exposed dry acclimated and wet rehydrated snails to low temperatures to determine temperature of crystallisation (Tc), lower lethal temperature and LT₅₀ and to examine the relationship between ice formation and mortality. Tc was lowest in dry Afrolittorina knysnaensis (–13.6±0.4 °C), followed by dry Echinolittorina natalensis (–10.9±0.2 °C) and wet A. knysnaensis (–10.2±0.2 °C). The Tc of both A. knysnaensis and E. natalensis increased with rehydration, whereas Tc of dry and wet Afrolittorina africana did not differ (–9.6±0.2 and –9.0±0.2 °C respectively). Wet snails of all species exhibited no or low survival of inoculative freezing, whereas dry individuals of A. knysnaensis could survive subzero temperatures above –8 °C when freezing was inoculated with ice. In the absence of external ice, Afrolittorina knysnaensis employs a freeze-avoidance strategy of cold tolerance, the first time this has been reported for an intertidal snail, indicating that there is no family-level phylogenetic constraint to freeze tolerance. Echinolittorina natalensis and A. africana both showed pre-freeze mortality and survival of some internal ice formation, but were not cold hardy in any strict sense.     

Tolypocladium cylindrosporum (Deuteromycotina: Moniliales), a fungal pathogen of the mosquito Aedes australis

The New Zealand strain of Tolypocladium cylindrosporum was cultured on Sabouraud dextrose agar medium under varying regimes of growth conditions. The isolate exhibited good tolerances to temperature (4–35 °C), pH (3–10) and salinity (0–7% NaCl). Optimal vegetative growth and sporulation were recorded between a temperature range of 20–30° C, pH of 5–6 and a salinity level of 0–2% NaCl. The North American isolate of the fungus showed similar tolerances, while the European isolate was less tolerant.     

Effect of incubation temperature on green sturgeon embryos, <Emphasis Type="Italic">Acipenser medirostris</Emphasis>

Regulation of river flow and the amount of winter rainfall are the major factors affecting the water temperature of the spawning grounds, for green sturgeon in the Klamath River. During the primary spawning period of green sturgeon, mid-April to June, the water temperature may vary from 8 to 21°C. To estimate the potential implications of this modified thermal regime, we examined the survival and development in three progeny groups of green sturgeon embryos from zygote to hatch, at constant incubation temperatures (11–26°C). Temperatures 23–26°C affected cleavage and gastrulation and all died before hatch. Temperatures 17.5–22°C were suboptimal as an increasing number of embryos developed abnormally and hatching success decreased at 20.5–22°C, although the tolerance to these temperatures varied between progenies. The lower temperature limit was not evident from this study, although hatching rate decreased at 11°C and hatched embryos were shorter, compared to 14°C. The mean total length of hatched embryos decreased with increasing temperature, although their wet and dry weight remained relatively constant. We concluded that temperatures 17–18°C may be the upper limit of the thermal optima for green sturgeon embryos, and that the river thermal regime during dry years may affect green sturgeon reproduction.     

Freeze tolerance in larvae of the winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae): a contrast to adult strategy for survival at low temperatures

The winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae) is freeze intolerant in the adult stage with a low mean supercooling point (SCP) of ~−20 °C. However, cold-hardiness strategies for immatures of this species are unknown. In this study, we measured SCP values for D. mendotae larvae, pupae and adults using surface-contact thermometry. In addition, the lower lethal temperature (LLT) was determined for the larval stage. The mean SCPs for larvae (−7.4 °C) and pupae (−9.1 °C) were relatively high compared to adults (−19.7 °C). Our results indicate that the larvae of D. mendotae are freeze tolerant with a LLT₉₉ (−25.4 °C), ~−10 °C lower than their minimum SCP (−15.6 °C). Freeze tolerance in these larvae may be a strategy to provide protection from short-term exposures to ice crystals or to permit diapause within frozen substrates. The change in cold-hardiness strategy from freeze tolerant to freeze intolerant between the larval and adult stages of this species is likely a result of the different habitats occupied by these two life stages.     

Cold hardiness and winter survival of the grape berry moth, Endopiza viteana, in New York State

Laboratory and field investigations were undertaken to evaluate the effect of winter mortality on subsequent infestation levels of the grape berry moth (GBM), Endopiza viteana (Clemens) (Lepidoptera: Tortricidae). Supercooling points (SCP) were used as a measure of the minimum survivable temperature for GBM pupae. The SCP of winter forms (diapausing) from a laboratory colony averaged –25.2 °C in December, –24.3 °C in March, and –24.0 °C in April. When diapausing pupae from a laboratory colony were placed in the field from December to March, the SCP averaged –23.3 °C. The SCP of summer forms from a laboratory colony averaged –21.6 °C in March. Significant levels of mortality (ca. 80%) of diapausing GBM pupae were observed after 24 h at –21 °C. Comparable mortality occurred after 1-week at –15 °C. Eighty-four percent of diapausing pupae survived for 8-months at 3 °C; non diapausing pupae suffered high levels of mortality (ca. 60%) after only 7-days at 3 °C. Field survival of diapausing pupae were significantly greater at soil level than 1-meter above the soil. Pupal survival was greater at 75% r.h. than at 0% or ambient r.h.. In 1986–1987 and 1987–1988, pupae covered with snow or leaf-litter had higher of survival than exposed pupae although these differences were only statistically significant in 1986–1987. The above findings are discussed within the context of potential implications to management strategies for GBM.

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Zusammenfassung Labor und Freilandversuche wurden unternommen um den potenziellen Einfluss von Wintersterben auf subsequenten Wurmbefall des nordamerikanischen Traubenwicklers Endopiza viteana (Clemens) (Lepidoptera: Tortricidae) auszuwerten. Die niedrigste Temperatur wobei Puppen ueberleben konnten ist durch Ueberkuehlungstemperaturen der Puppen gemessen worden. Fuer das ueberwinternde Stadium (in Diapause) einer Laborkolonie lag diese Temperatur durchschnittlich bei minus 25.2 °C in Dezember, minus 24.3 °C in Maerz, und minus 24.0 °C in April. Der Ueberkuehlungspunkt lag um minus 23.3 °C im Durchschnitt fuer Laborkolonie Puppen die waehrend der Diapause von Dezember bis Maerz im Freiland ausgesetzt wurden. Der Ueberkuehlungspunkt von Sommerstadien von der gleichen Kolonie lag im Vergleich um minus 21.6 °C im Maerz. Signifikante Sterblichkeit (um 80%) der Traubenwicklerpuppen wurde bemerkt nach 24 Stunden bei minus 21 °C. Vergleichbar war die Sterblichkeit nach einer Woche bei minus 15 °C. Nach 8 Monaten bei 3 °C ueberlebten 84% der Puppen in Diapause; 60% der Puppen nicht in Diapause starben nach 7 Tage bei 3 °C. Das Ueberlebensprozent diapausierender Puppen im Freien war signifikant hoeher auf der Erdoberflaeche als fuer die 1 m ueber der Oberflaeche. Mehr Puppen ueberlebten bei 75% relativer Luftfeuchtigkeit als bei 0% oder umgebender Luftfeuchtigkeit. In 1986–1987 und 1987–1988 Puppen die mit Schnee oder Laub bedeckt waren, ueberlebten prozentual mehr als die ohne jedes Bedeckungsmaterial. Die Ergebnisse werden im Kontext ihrer potenzieller Verwendung fuer Kontrolle des Traubenwicklers diskutiert.

     

Thermotolerant single cell protein production byKluyveromyces marxianus var.marxianus

Summary Amino acid analyses were undertaken on single cell protein (SCP) produced by thermotolerant strains ofKluyveromyces marxianus var.marxianus grown on sugar cane molasses at 40°C. The maximum conversion of available sugars to biomass at 45°C was only 10.8% (g dry wt.·g^–1 total sugars). The amino acid composition of the SCP did not differ markedly from that reported for other yeast species.     

Critical thermal limits, temperature tolerance and water balance of a sub-Antarctic kelp fly, Paractora dreuxi (Diptera: Helcomyzidae)

Paractora dreuxi displays distinct ontogenetic differences in thermal tolerance and water balance. Larvae are moderately freeze tolerant. Mean larval onset of chill coma was -5.1 degrees C, and onset of heat stupor was 35.5 degrees C. Larval supercooling point (SCP) was -3.3 degrees C with 100% recovery, although mortality was high below -4 degrees C. Starvation caused SCP depression in the larvae. Adults were significantly less tolerant, with critical thermal limits of -2.7 and 30.2 degrees C, no survival below the SCP (-9.6 degrees C), and no change in SCP with starvation. Moderate freeze tolerance in the larvae supports the contention that this strategy is common in insects from southern, oceanic islands. Fly larvae survived desiccation in dry air for 30 h, and are thus less desiccation tolerant than most other sub-Antarctic insect larvae. Water loss rates of the adults were significantly lower than those of the larvae. Lipid metabolism did not contribute significantly to water replacement in larvae, which replaced lost body water by drinking fresh water, but not sea water. Kelp fly larvae had excellent haemolymph osmoregulatory abilities. Current climate change has led to increased temperatures and decreased rainfall on Marion Island. These changes are likely to have significant effects on P. dreuxi, and pronounced physiological regulation in larvae suggests that they will be most susceptible to such change.     

Thermal tolerance limits in six weevil species (Coleoptera, Curculionidae) from sub-Antarctic Marion Island

Supercooling points, lower lethal temperatures, and the effect of short-term exposures to low temperatures were examined during both winter and summer in the adults of six weevil species from three different habitats on Marion Island. Upper lethal limits and the effects of short-term exposure to high temperatures were also examined in summer-acclimatized adult individuals of these species. Bothrometopus elongatus, B. parvulus, B. randi, Ectemnorhinus marioni, and E. similis were freeze tolerant, but had high lower lethal temperatures (−7 to −10°C). Seasonal variation in these parameters was not pronounced. Physical conditions of the habitat appeared to have little effect on cold hardiness parameters because the Ectemnorhinus species occur in very wet habitats, whereas the Bothrometopus species inhabit drier areas. The adults of these weevil species are similar to other high southern latitude insects in that they are freeze tolerant, but with high lower lethal temperatures. In contrast, Palirhoeus eatoni, a supra-littoral species, avoided freezing and had a mean supercooling point of −15.5 ± 0.94°C (SE) in winter and −11.8 ± 0.98°C in summer. Survival of a constant low temperature of −8°C also increased in this species from 6 h in summer to 27 h in winter. It is suggested that this strategy may be a consequence of the osmoregulatory requirements imposed on this species by its supra-littoral habitat. Upper lethal temperatures (31–34°C) corresponded closely with maximum microclimate temperatures in all of the species. This indicates that the pronounced warming, accompanied by the increased insolation that has been recorded at Marion Island, may reduce survival of these species. These effects may be compounded as a consequence of predation by feral house mice on the weevils. Received: 4 February 1997 / Accepted: 3 May 1997     

Mean geocarposphere temperatures that induce preharvest aflatoxin contamination of peanuts under drought stress

Apparently undamaged peanuts grown under environmental stress in the form of drought and heat become contaminated with Aspergillus flavus and aflatoxin in the soil prior to harvest. The upper mean temperature limit for aflatoxin contamination in undamaged peanut kernels grown under drought stress the latter 4–6 weeks of the growing season was between 29.6–31.3°C. The lower limit was between 25.7–26.3°C. That is, peanuts grown under drought stress with a mean geocarposphere temperature of 29.6°C were highly contaminated while those at 31.3°C were not contaminated. Likewise, those grown under drought stress with a mean geocarposphere temperature of 25.7°C were not contaminated while those subjected to a mean geocarposphere temperature of 26.0°C resulted in some categories becoming contaminated. Increasing the mean temperature up to 29.6°C caused increasing amounts of contamination.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

A Comparative Analysis of the Ice Nucleation Activity of Pseudomonad Cells and Lipopolysaccharides

The paper deals with the study of the ice nucleation activity of the cells, extracellular lipopolysaccharides (ELPSs), lipopolysaccharides (LPSs), and LPS structural components (lipid A, core oligosaccharide, and O-specific polysaccharide) of Pseudomonas fluorescens, P. syringae, P. fragi, and P. pseudoalcaligenes. Aqueous suspensions of intact cells of P. syringae IMV 1951 and IMV 185 began to freeze at –1 and –4°C, respectively. This suggests that these cells possess ice nucleation activity. Aqueous cell suspensions of two other strains, P. fluorescens IMV 1433 and IMV 2125, began to freeze at lower temperatures than did distilled water (–9°C), which suggests that the cells of these strains possess antifreeze activity. The ice nucleation activity of the bacterial strains studied did not show any correlation with their taxonomic status. The ice nucleation activity of ELPSs depended little on their concentration (within a concentration range of 0.2–0.4%). In most cases, the ice nucleation activity of ELPSs, LPSs, and LPS structural components differed from that of the intact cells from which these biopolymers were obtained. This may indicate that the biopolymers under study play a role in ice nucleation but this role is not crucial. The relationship between the structure of LPSs and their effect on ice nucleation is discussed.