Overwintering ecology of alpine Collembola and oribatid mites from the Austrian Alps

Abstract. 1. Collembola and oribatid mites from windswept mountain ridges at about 2700 m a.s.l. in the Austrian Alps were all killed by freezing, and depend on supercooling to survive low winter temperatures. The Collembola Tetracanthella afurcata Handschin, Xenylla acauda Gisin and Isotoma spp. collected in January had average supercooling points between -25 and -29°C, and the oribatid mites Fuscozetes fuscipes (Koch) and Lepidozetes singularis Berlese of about -28 and -31°C respectively. The ability to supercool was not increased during storage at -5°C, and was generally lower in species collected in March.
2. The oribatid mites Fuscozetes intermedius Caroli and Maffia, F. fuscipes, Damaeus diversipilis (Willmann) and L.singularis contained from 9 to 16 μg glycerol per mg fresh weight after storage at -5°C, while no glycerol could be detected in the Collembola Isotoma spp., T.afurcata and Onychiurus vontoernei Gisin.
3. Activity below 0°C was observed in T.afurcata and O.vontoernei , which had chill-coma temperatures of -7.7 and -4.9°C respectively.
4. Some specimens of F.intermedius survived more than 90 days of anoxia at 0°C, T.afurcata up to 60 days and O.vontoernei up to 24 days.
5. The overwintering biology of Collembola and oribatid mites from the Austrian Alps appears similar to that of Norwegian species, except that those from Austria have slightly lower supercooling points and higher contents of glycerol.     

The role of direct chilling injury and inoculative freezing in cold tolerance of Amblyomma americanum, Dermacentor variabilis and Ixodes scapularis

Abstract. Supercooling points and chill tolerance were compared among nymphs and adults of the ixodid ticks Dermacentor variabilis, Amblyomma americanum and Ixodes scapularis (Acari: Ixodidae).Supercooling points in the range of <-22 to -18°C were observed for nymphs, and -22 to -8°C for adults.The lower lethal temperatures observed under dry conditions, -14 to -10°C, were warmer than the supercooling points, but still much colder than -4.8°C, the lowest temperature recorded from a likely tick habitat in southwestern Ohio.Based on our experiments, spontaneous freezing and direct chilling injury are not significant mortality factors in these species in the field.Mortality was observed between -5 and -3°C for A.americanum and D.variabilis nymphs chilled for 2 h while in direct contact with ice.This mortality is probably due to inoculative freezing.Given the requirement for a rather humid microhabitat for off-host survival, these findings suggest that inoculative freezing is an important cause of overwintering mortality in these medically important species.     

The effect of feeding on specific soil algae on the cold-hardiness of two Antarctic micro-arthropods (Alaskozetes antarcticus and Cryptopygus antarcticus)

The effect of consuming terrestrial algae on the cold tolerance of two Antarctic micro-arthropods was examined. From the results of preferential feeding experiments, seven species of Antarctic terrestrial micro-algae were chosen and fed to two common, freeze-avoiding Antarctic micro-arthropods: the springtail Cryptopygus antarcticus (Collembola: Isotomidae), and the mite Alaskozetes antarcticus (Acari: Oribatida). Mites were very selective in their choice of food whereas the springtails were less discriminating. The ice nucleating activity of each species of alga was measured using an ice nucleator spectrometer and a differential scanning calorimeter. Pure cultures of individual species of algae had characteristic supercooling points ranging from ca. −5 to −18 °C. The effect of eating a particular alga on the supercooling point of individual micro-arthropods cultured at two different temperatures (0 and 10 °C) was examined. Neither species showed a preference for algae with low ice-nucleating activity and there was no clear correlation between the supercooling point of food material and that of the whole animal. However, feeding on certain algae such as Prasiola crispa, which contained the most active ice nucleators, decreased the cold tolerance of both species of arthropods. Accepted: 6 May 2000     

Low temperature effects on micro-arthropods

The main features of the cold hardiness strategies adopted by Antarctic terrestrial arthropods (principally Acari and Collembola) are reviewed. These include lethal low temperatures, chill-coma temperature, supercooling ability, cryoprotectants and survival in anoxic conditions.     

Adaptations to low temperature in high altitude insects from Mount Kenya

Abstract. 1. The strategies for low temperature survival in insects on Mount Kenya were investigated. The insects were collected from their natural habitats and their supercooling points and low temperature tolerances determined.
2. Most insects showed no special adaptations to low temperature survival and seem to depend on spending the cold nights in protected habitats, such as beneath stones and fallen trunks of plants, as well as within the wet frills of dead leaves of alpine plants, where they are protected by the heat released from freezing water.
3. Some insects, e.g. Collembola, aphids and a curculionid beetle, which live in relatively unprotected habitats, had low supercooling points, allowing them to remain unfrozen when exposed to low night temperatures. A nucleator free diet is apparently essential for the survival of such species.
4. Two species of curculionid beetles were found to withstand freezing down to -7C. These beetles had nucleating agents in their haemolymph and higher supercooling points than most of the other species studied.
5. A moderate freezing tolerance was found in larvae of a midge that lives in the watery liquid between the leaves of Senecio brassica .     

COLD TOLERANCE OF MICROARTHROPODS

1. Microarthropods (Acari and Collembola) are dominant components of the terrestrial fauna in the Antarctic. Their cold tolerance, which forms the mainspring of their adaptational strategy, is reviewed against a background of their structure and function, and by comparison with other arthropods. 2. Two species, the isotomid collembolan Cryptopygus antarcticus Willem and the oribatid mite Alaskozetes antarcticus (Michael), are examined in detail, and afford a comparative approach to the mechanisms underlying cold tolerance in insect and arachnid types. 3. All microarthropods appear to be freezing-susceptible (unable to tolerate tissue ice), and they utilize varying levels of supercooling to avoid freezing. Gut contents are considered to be the prime nucleation site in most arthropods when supercooled, particularly for Antarctic species. Moulting also increases individual supercooling ability especially in Collembola, and the activity of ice-nucleating bacteria in cold-hardy arthropods may be important. 4. Sources of ice nucleators are many and varied, originating externally (motes) or internally (ice-nucleating agents). They act either extracellularly (mainly in the haemolymph) to promote freezing in ice-tolerant life stages, or intracellularly in freezing-susceptible forms. Thermal hysteresis proteins, acting colligatively, occur in many arthropods including Collembola; they depress both the freezing point of body fluids and the whole-body supercooling point of freezing- susceptible and freezing-tolerant species. 5. Bimodal supercooling point distributions are a feature of microarthropods and water droplets. Samples of field populations of Antarctic mites and springtails show significant seasonal changes in these distributions, which in some respects are analogous to purely physical systems of water droplets. Supercooling points are confirmed as accurate measures of cold-hardiness and survival for Antarctic species, but not necessarily for other arthropods. The effects of constant sub-zero temperatures approaching the limit of the supercooling ability of arthropods require study. 6. Desiccation and dehydration influence microarthropod physiology in several ways; in Alaskozetes it triggers glycerol synthesis. Glycerol may aid binding of water in severely dehydrated insects, but the relationship of such ‘bound’ water to cold-hardiness is unclear. 7. Sugar alcohols (polyols) and sugars are accumulated as potential cryoprotectants in many arthropods at low temperatures, and antifreeze systems may be single or multi-component in structure. Cryoprotectant synthesis and regulation have been studied principally in insects, and fresh weight concentrations of 0–3-5 M of polyols have been found. Trehalose accumulation may also influence cold-hardiness. 8. Microarthropods fall within the spectrum of cold tolerance observed for arthropods and other invertebrates. No special adaptations are found in Antarctic species, and similar strategies and mechanisms are present in both insects and arachnids. The colonization and maintenance of microarthropod populations of polar land habitats seem not to have required the evolution of any novel features with respect to cold tolerance.     

Cold tolerance of micro-arthropods from Alaskan taiga

Abstract. Mean supercooling points for a variety of soil and litter arthropods including mites, springtails, a heteropteran and immature spiders from a central Alaskan taiga site ranged from -6.3 to -28.5°C during autumn. Variation in supercooling ability of five species of cryptostigmatid mites occurred throughout the year with increased cold tolerance in autumn and early winter concomitant with the temperature pattern of the habitat. No correlation between the level of supercooling and water content of the mites was evident. Changes in the frequency distribution of individual supercooling points occurred in autumn, winter, spring and summer samples which were species specific. All arthropods tested were susceptible to freezing, and the mites utilize supercooling to avoid freezing.     

Cold tolerance of alpine,Arctic, and Antarctic Collembola and mites

Because of their dominant role in the fauna of alpine, Arctic and Antarctic locations Collembola and mites are of particular interest regarding adaptations to low temperatures. No freezing-tolerant species have been found in these groups of terrestrial arthropods, and it appears that all species depend entirely on supercooling to survive the lower temperatures of their habitats. While summer animals have high supercooling points, an increase in supercooling ability occurs during autumn and early winter, and can be explained as a two-step process. Initially gut content has to be eliminated to avoid heterogeneous nucleation at high subzero temperatures due to foreign nucleating agents. Second, supercooling is further enhanced through accumulation of glycerol or other lowmolecular cryoprotective substances. Further studies are needed on the ability of such animals to avoid inoculative freezing in their microhabitats.     

Geographical variation in egg cold hardiness: a study on the adaptation strategies of the migratory locust Locusta migratoria L.

Abstract. 1. For many species of insect, cold hardiness is an important trait that enables a population to develop in the next season and to extend its range. To elucidate the role of cold hardiness of the migratory locust Locusta migratoria L. in its outbreak and distribution areas, egg cold hardiness was examined in locusts derived from four locations from latitude 18°23'N to latitude 41°10'N in eastern China.
2. The supercooling points of eggs from different geographic populations did not differ significantly for the first development stage, with an average ± SE of −24.5 ± 0.51 °C, or for the second stage, −22.06 ± 0.68 °C, however there was a significant difference for the embryonic development phase among the four geographical populations. The egg supercooling point increased gradually from neonatal egg to old egg; eggs prior to hatching always had a much higher supercooling point.
3. Comparisons of the cold hardiness of four populations were carried out by validating the close correlation between latitude and the effects of cold on hatching, low lethal temperature (Ltemp₅₀), and low lethal time (Ltime₅₀). There were significant differences among the four populations; the northern population was more cold hardy than the southern population, and the two mid-latitude populations were intermediately cold hardy.
4. The cold hardiness of all populations was enhanced to various degrees by short-term cold acclimation at 0 °C and 5 °C. For most populations, a 2-day acclimation period seemed to be optimal.     

Seasonal changes in soil arthropod abundance in the dry evergreen forest of north-east Thailand,with special reference to collembolan communities

A soil arthropod community was studied in a dry evergreen forest over a 3-year period from May 1998 to April 2001. Population abundance, species composition, and community structure were investigated over the 3-year study period. The soil arthropods consisted of Acari (75.38%), Collembola (16.11%), and others (8.51%), and their abundances showed a clear difference between the rainy and dry seasons. Population abundance of Collembola and Acari were low during drought conditions. The humidity was the most important factor determining distribution, abundance, and survival of soil Collembola in this tropical forest. High predation and low accumulation of organic matter caused low population abundance of Collembola in the tropical habitat. The collembolan community was dominated by a few dominant species over the study period. The pattern of seasonal changes in numbers of Collembola was similar over the 3-year study period. The species composition of the collembolan community was constant and persistent throughout a 3-year study period. Thus, the collembolan community showed constancy in its species composition with seasonal variability over the 3-year study period.     

Cold-hardiness and development of eggs of Rhopalosiphum insertum

Abstract. 1. The eggs of Rhopalosiphum insertum (Walker) showed a seasonal increase in cold-hardiness under field conditions. Their supercooling point fell from -35°C in November to below -40°C in January, then rose to-35°C or above by March.
2. Laboratory experiments demonstrated that both temperature and date affected cold-hardiness of the eggs. The supercooling points of eggs kept at 16 h photoperiod or in darkness did not, however, differ significantly.
3. Eggs brought from the field into warm, long-day conditions would not hatch until after mid-January. After this date, per cent hatch was significantly greater in 16 h photoperiod than in darkness; it did not differ between eggs kept at 5 or 0°C, but was reduced at -5°C.
4. It is concluded that eggs of Rinserturn are in diapause until mid-January, and that hatching rate and cold-hardiness are determined by separate environmental factors.     

Deep supercooling xylem parenchyma cells of katsura tree (Cercidiphyllum japonicum) contain flavonol glycosides exhibiting high anti-ice nucleation activity

Xylem parenchyma cells (XPCs) of boreal hardwood species adapt to sub-freezing temperatures by deep supercooling to maintain a liquid state of intracellular water near −40 °C. Our previous study found that crude xylem extracts from such tree species exhibited anti-ice nucleation activity to promote supercooling of water. In the present study, thus, we attempted to identify the causative substances of supercooling. Crude xylem extracts from katsura tree ( Cercidiphyllum japonicum ), of which XPCs exhibited deep supercooling to −40 °C, were prepared by methanol extraction. The crude extracts were purified by liquid–liquid extraction and then by silica gel column chromatography. Although all the fractions obtained after each purification step exhibited some levels of anti-ice nucleation activity, only the most active fraction was retained to proceed to the subsequent level of purification. High-performance liquid chromatography (HPLC) analysis of a fraction with the highest level of activity revealed four peaks with high levels of anti-ice nucleation activity in the range of 2.8–9.0 °C. Ultraviolet (UV), mass and nuclear magnetic resonance (NMR) spectra revealed that these four peaks corresponded to quercetin-3- O - β -glucoside (Q3G), kaempferol-7- O - β -glucoside (K7G), 8-methoxykaempferol-3- O - β -glucoside (8MK3G) and kaempferol-3- O - β -glucoside (K3G). Microscopic observations confirmed the presence of flavonoids in cytoplasms of XPCs. These results suggest that diverse kinds of anti-ice nucleation substances, including flavonol glycosides, may have important roles in deep supercooling of XPCs.     

长期施肥对黄淮海平原农田中小型土壤节肢动物的影响

在2008年9月和2009年2月,采用改良干漏斗方法(Modified Tullgren)对黄淮海地区长期定位施肥试验下中小型土壤节肢动物进行调查。试验包括氮磷钾(NPK)、氮磷(NP)、氮钾(NK)、磷钾(PK)、有机肥(OM)、1∶1化学氮肥与有机氮肥(OMNPK)和不施肥(CK)7个处理。结果表明:OM和OMNPK处理有利于提高土壤动物丰富度和多样性;NK处理不利于土壤动物的生存和发展,缺磷影响了土壤动物数量的增长;从优势类群弹尾目和蜱螨目来看,OM和OMNPK处理对弹尾目等节跳科、棘跳科和球角跳科的生长有利,而圆跳科在NPK处理下具有更高的数量;OMNPK处理对蜱螨目中气门亚目有显著的正效应,对前气门亚目和甲螨亚目也有一定的正向作用;氮肥对弹尾目没有表现出正相关关系,但在一定程度上增加了蜱螨目的数量。     

Habitat temperature and the temporal scaling of cold hardening in the high Arctic collembolan, Hypogastrura tullbergi (Schäffer)

Abstract.  1. Cold tolerance is a fundamental adaptation of insects to high latitudes. Flexibility in the cold hardening process, in turn, provides a useful indicator of the extent to which polar insects can respond to spatial and temporal variability in habitat temperature.
2. A scaling approach was adopted to investigate flexibility in the cold tolerance of the high Arctic collembolan, Hypogastrura tullbergi , over different time-scales. The cold hardiness of animals was compared from diurnal warming and cooling phases in the field, and controlled acclimation and cooling treatments in the laboratory. Plasticity in acclimation responses was examined using three parameters: low temperature survival, cold shock survival, and supercooling points (SCPs).
3. Over time-scales of 24–48 h, both field animals from warm diurnal phases and laboratory cultures from a 'warm' acclimation regime (18 °C) consistently showed greater or equivalent cold hardiness to animals from cool diurnal phases and acclimation regimes (3 °C).
4. No significant evidence was found of low temperature acclimation after either hours or days of low temperature exposure. The cold hardiness of H. tullbergi remained 'seasonal' in character and mortality throughout was indicative of the summer state of acclimatization.
5. These data suggest that H. tullbergi employs an 'all or nothing' cryoprotective strategy, cold hardening at seasonal but not diel-temporal scales.
6. It is hypothesised that rapid cold hardening offers little advantage to these high Arctic arthropods because sub-zero habitat temperatures during the summer on West Spitsbergen are rare and behavioural migration into soil profiles offers sufficient buffering against low summer temperatures.     

Seasonal variation in freezing tolerance of the New Zealand alpine cockroach Celatoblatta quinquemaculata

1. The cold hardiness of the alpine cockroach Celatoblatta quinquemaculata was investigated. This species is found at 1360 m a.s.l. beneath schist slabs on the Rock and Pillar Range (Central Otago, New Zealand). Cockroaches were collected monthly from January to December 1996, and their LT₅₀ and supercooling points determined.
2. Celatoblatta quinquemaculata was freezing tolerant throughout the year, with a lower lethal temperature in winter of – 8.9 °C. Celatoblatta quinquemaculata was also found frozen under rocks in the field when the under-rock temperature was below – 3 °C, and could survive being frozen at – 5 °C for 4 days in the laboratory.
3. There was a marked decrease in LT₅₀ temperature from – 5.5 °C in April to – 7.5 °C in May. This coincides with decreasing temperatures from summer through autumn to winter, during which temperatures beneath snow-covered rocks may reach – 7.3 °C.
4. Supercooling points fluctuated during the year, with an increase from – 4.2 °C in autumn to – 3.4 °C in winter. Supercooling point was highest in spring, and changes in supercooling point do not appear to be related to changes in LT₅₀.
5. Recordings of environmental temperatures from the Rock and Pillar Range suggest that cockroaches may undergo up to twenty-three freeze–thaw cycles in the coldest month of the year, and that they may remain frozen for periods of up to 21 h. Maximum cooling rates recorded in the field (0.01 °C min^–1) were 100-fold slower than laboratory cooling rates, so survival estimates from laboratory experiments may be underestimates.     

ADAPTATIONS OF TERRESTRIAL ARTHROPODS TO THE ALPINE ENVIRONMENT

1. The climate changes drastically above the timberline. Diverse adaptations have been evolved by insects and other terrestrial arthropods to survive the alpine environment. The fitness of each species depends on a combination of different factors in accordance with their special habitats. 2. Morphological adaptations such as reduced body-size, are known from a number of alpine insects, increasing their possibility to find sheltered microhabitats. Selection for reduced body size in Andean Phulia spp. butterflies is probably a result of their rigorous environment. Wing atrophy, which is also known in insects from other extreme environments, is widespread in alpine species. In several terrestrial arthropods the absorption of solar radiation is increased by melanism. Increased pubescence, protecting against the loss of heat, is known in alpine butterflies and bumblebees. 3. Several behavioural adaptations are described. Thermoregulatory behaviour is important in many species to raise their body temperatures. Alpine butterflies orient the dark basis of their wings perpendicular to the rays of the sun. Body temperatures of 30 °C may be required for flight. To increase their activities many alpine terrestrial arthropods seek warmer microhabitats in the vegetation and under rocks. The adaptive advantage of nocturnal activity as observed in several species, may be to maintain the water balance or to avoid predation. 4. Tropical alpine terrestrial arthropods are faced with special problems. The large diel temperature fluctuations require cold-hardiness during the night and tolerance to heat during the day. Many species seek sheltered microhabitats under rocks and in vegetation. 5. Due to low precipitation and high evaporation rates many mountain areas are extremely dry. High resistance to desiccation may be very important to alpine species, and in particular to tropical species. Rates of water loss at low relative humidities are comparable to those of desert arthropods. 6. As an adaptation to the cold alpine summers several species of terrestrial arthropods require more than one year to complete their life-cycles. Special to these species is their adaptation to low temperatures in two or more overwintering stages. In spite of their cold surroundings several species have univoltine life cycles, frequently combined with highly specialized adaptations. Increased metabolic rates as a compensation to low temperatures may be widespread in alpine species, but few data are available. 7. Cold tolerance is of particular importance in temperature alpine species. Winter survival in Collembola and Acari depends on supercooling. Great seasonal variations have been observed in a number of species. Freezing tolerance is also known from alpine insects, e.g. in some species of beetles. At high latitudes alpine species must endure periods of up to eight or nine month at low temperatures during hibernation. Anaerobiosis is known from species that are enclosed in ice, with lactate as the main end product of metabolism.     

Desiccation stress at sub-zero temperatures in polar terrestrial arthropods

Cold tolerant polar terrestrial arthropods have evolved a range of survival strategies which enable them to survive the most extreme environmental conditions (cold and drought) they are likely to encounter. Some species are classified as being freeze tolerant but the majority of those found in the Antarctic survive sub-zero temperatures by avoiding freezing by supercooling. For many arthropods, not just polar species, survival of desiccating conditions is equally important to survival of low temperatures. At sub-zero temperatures freeze avoiding arthropods are susceptible to desiccation and may lose water due to a vapour diffusion gradient between their supercooled body fluids and ice in their surroundings. This process ceases once the body fluids are frozen and so is not a problem for freeze tolerant species. This paper compares five polar arthropods, which have evolved different low temperature survival strategies, and the effects of exposure to sub-zero temperatures on their supercooling points (SCP) and water contents. The Antarctic oribatid mite (Alaskozetes antarcticus) reduced its supercooling point temperature from -6 to -30 degrees C, when exposed to decreasing sub-zero temperatures (cooled from 5 to -10 degrees C over 42 days) with little loss of body water during that period. However, Cryptopygus antarcticus, a springtail which occupies similar habitats in the Antarctic, showed a decrease in both water content and supercooling ability when exposed to the same experimental protocol. Both these Antarctic arthropods have evolved a freeze avoiding survival strategy. The Arctic springtail (Onychiurus arcticus), which is also freeze avoiding, dehydrated (from 2.4 to 0.7 g water g(-1) dry weight) at sub-zero temperatures and its SCP was lowered from c. -3 to below -15 degrees C in direct response to temperature (5 to -5.5 degrees C). In contrast, the freeze tolerant larvae of an Arctic fly (Heleomyza borealis) froze at c. -7 degrees C with little change in water content or SCP during further cold exposure and survived frozen to -60 degrees C. The partially freeze tolerant sub-Antarctic beetle Hydromedion sparsutum froze at c. -2 degrees C and is known to survive frozen to -8 degrees C. During the sub-zero temperature treatment, its water content reduced until it froze and then remained constant. The survival strategies of such freeze tolerant and freeze avoiding arthropods are discussed in relation to desiccation at sub-zero temperatures and the evolution of strategies of cold tolerance.     

Ecology of Cryptopygus sverdrupi (Insecta: Collembola) from Dronning Maud Land,Antarctica

Summary Observations on the ecology of Cryptopygus sverdrupi Lawrence (Collembola, Isotomidae) were made with specimens from the Mühlig-Hofmannfjella, Dronning Maud Land, Antarctica. At an elevation of 1600 m a.s.l. the species was numerous in association with the green alga Prasiola on gravel fields and in crevices of large boulders. The distribution of size-classes in field samples suggested that the population comprised several overlapping generations. Growth and development is probably very slow due to long winters and daily periods of subzero temperatures in their microhabitat during the summer. Specimens collected in mid-January had a mean supercooling point of-24.6°C with small individual variations. The lack of high supercooling points in the summer suggests that the springtails feed on a nuleatorfree diet. The ability to supercool was increased during prolonged starvation and acclimation at 0,-4 and-8°C. Glycerol and other potential low molecular weight cryoprotective substances were demonstrated in specimens acclimated at-4 and-8°C. The species possessed a relatively high tolerance to desiccation.Publication No. 81 of the Norwegian Antarctic Research Expeditions (1984/85)     

The effects of foliar pubescence and nutrient enrichment on arthropod communities of Metrosideros polymorpha (Myrtaceae)

Abstract.  1. Nutrient resource availability and host-plant foliar pubescence both influence arthropod food webs, but multifactor studies are needed to understand their interdependence and relative importance. Arthropods were sampled by clipping foliage from Metrosideros polymorpha (Myrtaceae) trees of pubescent, glabrous, and intermediate leaf forms on fertilised and unfertilised plots.
2. Fertilisation decreased leaf mass per area (LMA) but did not change the relative mass of pubescence within leaf morphological classes.
3. Fertilisation increased densities of individuals in four taxonomic orders, densities of individuals and species of all trophic levels, and the biomass of Collembola and Homoptera. Herbivore relative diversity (Shannon H ') also increased with fertilisation, but detritivore diversity declined due to increasing dominance of Salina celebensis (Schaeffer) (Collembola).
4. Detritivore density, driven again by S. celebensis , increased with decreasing leaf pubescence, but Heteroptera and Acari were most abundant on the intermediate pubescence class, and Psocoptera density and biomass increased with increasing pubescence. Trophic-level species density did not change with leaf morphological class, but relative diversity of all arthropods and of detritivores increased with increasing pubescence.
5. Both resource availability and leaf pubescence affected Metrosideros arthropod communities. However, the pervasive positive influence of fertilisation did not translate to compositional shifts, and there were no interactions with leaf morphological class. In contrast, the effects of leaf pubescence on arthropod density, biomass, and diversity were more restricted taxonomically, and non-parametric manova and redundancy analyses demonstrated significant differentiation in community composition on the pubescent morphology.     

Overwintering survivorship of pupae of the mimosa web worm, Homadaula anisocentra (Lepidoptera: Plutellidae), in an urban landscape

ABSTRACT. 1. Overwintering survivorship of pupae of the mimosa webworm, Homadaula anisocentra Meyrick (Lepidoptera: Plutellidae), was examined in several urban habitats in central Iowa during the winters of 1981–82, 1982–83 and 1983–84.
2. Survivorship and supercooling point temperatures were determined throughout the winters. Corroborative laboratory studies were conducted during the winter of 1982–83.
3. Minimum ambient temperatures that equalled or were below the supercooling point of the insect, at any time, were lethal.
4. Prolonged cold exposure below 0°C and above the supercooling point resulted in high mortality levels. To quantify this relationship, a concept of minimum-temperature exposure was developed by tabulating the number of degrees that the daily minimum temperature was below 0°C for a given sampling period.
5. Some mimosa webworm pupae were found to overwinter in highly protected sites (2.5–5.0°C warmer than the ambient air temperatures) in the urban environment, resulting in less minimum-temperature exposure and reducing the probability of reaching the lethal supercooling point temperature.