Biology and ecology of theDusmoecetes Jeannel (Col. Curculionidae) species complex on Marion Island

Summary TheDusmoecetes species complex on sub-Antarctic Marion Island comprises two species. The larger species,D. similis (C.O. Waterhouse), feeds on angiosperms as adults and detritus as larvae, whereas the smaller species,D. marioni Jeannel feeds on bryophytes in all stages.D. similis has seven larval instars and a generation time of one year or longer.D. marioni has between five and seven larval instars, depending on the plant community it inhabits, and a generation time of one year or less. Immatures ofD. similis have a theoretical null point of development of -0.62°C and aQ ₁₀ of 3.57. In both species there are overlapping generations in the field, although in the case ofD. similis there is a distinct seasonal emergence of adults starting in September. Mean standing crop of larvae on the coastal plain is approximately 5.5 kg (dry mass)·ha^-1, but can be as high as 11.85 kg (dry mass)·ha^-1 inAzorella selago dominated communities. This study indicates that both species are important herbivores and/or detritivores on Marion Island.     

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     

Respiratory Metabolism of sub-Antarctic insects from different habitats on Marion Island

Oxygen uptake of the foliage-dwelling larvae ofEmbryonopsis halticella Eaton (Lepidoptera: Yponomeutidae) and adults ofEctemnorhinus marioni Jeannel (Coleoptera: Curculionidae), the litter-dwelling larvae ofPringleophaga marioni (Lepidoptera: Tineidae) and the wrack-dwellingParactora dreuxi Séguy (Diptera: Helcomyzidae) was examined over the range of temperatures experienced by these insects in their microhabitats. With the exception of the kelp fly,P. dreuxi, Q₁₀s and activation energies were generally lower than those found in temperate and Arctic insects, but were similar to values found in beetles from sub-Antarctic South Georgia Island. Q₁₀ and activation energy of each species reflected the temperature regime found in its microhabitat. Activation energies of the Marion Island species were intermediate between those found in temperate and polar arthropods, but towards the polar end of the range. The hypothesis that insects are capable of showing respiratory adaptation to temperature is supported.     

Similar metabolic rate-temperature relationships after acclimation at constant and fluctuating temperatures in caterpillars of a sub-Antarctic moth

Temperature compensation in whole-animal metabolic rate is one of the responses thought, controversially, to characterize insects from low temperature environments. Temperature compensation may either involve a change in absolute values of metabolic rates or a change in the slope of the metabolic rate – temperature relationship. Moreover, assessments of compensation may be complicated by animal responses to fluctuating temperatures. Here we examined whole animal metabolic rates, at 0 °C, 5 °C, 10 °C and 15 °C, in caterpillars of the sub-Antarctic moth, Pringleophaga marioni Viette (Tineidae), following one week acclimations to 5 °C, 10 °C and 15 °C, and fluctuating temperatures of 0–10 °C, 5–15 °C, and 10–20 °C. Over the short term, temperature compensation was found following acclimation to 5 °C, but the effect size was small (3–14%). By comparison with caterpillars of 13 other lepidopteran species, no effect of temperature compensation was present, with the relationship between metabolic rate and temperature having a Q₁₀ of 2 among species, and no effect of latitude on temperature-corrected metabolic rate. Fluctuating temperature acclimations for the most part had little effect compared with constant temperatures of the same mean value. Nonetheless, fluctuating temperatures of 5–15 °C resulted in lower metabolic rates at all test temperatures compared with constant 10 °C acclimation, in keeping with expectations from the literature. Absence of significant responses, or those of large effect, in metabolic rates in response to acclimation, may be a consequence of the unpredictable temperature variation over the short-term on sub-Antarctic Marion Island, to which P. marioni is endemic.     

Temperature variation across Marion Island associated with a keystone plant species (Azorella selago Hook. (Apiaceae))

Microclimate is the most appropriate measure of climate affecting species. Understanding microclimate variation is essential for predicting effects of climate change on species. This study examined (1) variation in microclimate temperatures associated with Azorella selago Hook. (Apiaceae) across Marion Island, (2) differences between microclimate temperature and meteorological station temperatures, and (3) effect of A. selago on microclimate temperatures. Microclimate temperatures were shown to vary significantly with altitude and island side. The microclimate associated with A. selago was also more extreme than meteorological station temperature ranges suggest. A. selago was shown to ameliorate temperature conditions compared to those on the ground. Given the biotic differences that have been documented between the sides of Marion Island, this finding argues strongly for improved understanding of spatial variability in Marion Island’s climate. Such understanding is particularly critical given the rapid rate of climate change currently being experienced by the island.     

The impact of a small, alien invertebrate on a sub-Antarctic terrestrial ecosystem: Limnophyes minimus (Diptera, Chironomidae) at Marion Island

Density and biomass of the larvae of a small, alien chironomid midge, Limnophyes minimus, whose parthenogenetic adult females do not feed, were quantified for ten major lowland plant communities at sub-Antarctic Marion Island (46°52′S 37°51′E) and compared with the density and biomass of indigenous macro-invertebrates in the same communities. An estimate of litter consumption by larvae of this midge was also made. L. minimus reached high densities in most of the plant communities sampled, with the highest density being recorded in the Cotula plumosa biotically influenced community (annual mean of 4,365 individuals m⁻²) and the lowest in the Crassula moschata salt spray community (annual mean of 41 individuals m⁻²). Estimates of litter ingestion indicated that L. minimus larvae are capable of consuming between 0.07 and 8.54 g_{(dry mass)} m⁻² per year, depending on the community. In some communities this litter consumption amounted to an order of magnitude more than that consumed by Pringleophaga marioni (Lepidoptera, Tineidae). Although the larvae of this moth species are thought to represent the bottleneck to nutrient recycling on the island, this study showed that midge larvae may also contribute substantially to this process. As a consequence, the considerable changes that have been predicted to occur in Marion Island's terrestrial ecosystem as a consequence of enhanced predation by mice on P. marioni larvae may be retarded or obscured by the contribution of the midge larvae to nutrient cycling. Hence, it is suggested that greater attention be given to the small and inconspicuous elements of the alien sub-Antarctic faunas because such species may have profound consequences for ecosystem functioning on these islands. Received: 17 November 1997 / Accepted: 23 February 1998     

Abundance and seasonality of mid-altitude fellfield arthropods from Marion Island

Fellfield is an important habitat in both the Antarctic and sub-Antarctic. However, few studies have examined the abundance and seasonality of arthropods in sub-Antarctic fellfield habitats. Here, soil arthropod communities were sampled for over a full year in two distinct habitat components (rocky areas and Azorella selago cushions) in a mid-altitude fellfield on Marion Island. Species richness was relatively high (42 spp.) and consisted almost exclusively of indigenous species. Maximum mean annual density in the A. selago cushions was 16,000 individuals m⁻² for Eupodes minutus. In contrast, the highest density of any species in the rocky, inter-cushion areas was 700 individuals m⁻² for Halozetes fulvus. Quantitative analyses highlighted prominent differences in arthropod community structure between the two habitat components, despite the fact that most species were common to both of them. In general, arthropod abundances were lower in the fellfield compared with less extreme vegetation types in the sub-Antarctic, but were not dissimilar to those found in fellfield in the maritime Antarctic. In the Marion Island fellfield, arthropods either showed no pronounced seasonal peak in abundance, or a summer peak, although these patterns differed between habitat components within species, and between species. These data provide a firm quantitative foundation for further investigations of community patterns and seasonality in sub-Antarctic fellfield arthropods. Accepted: 10 June 2000     

Chemosensory and thermal cue responses in the sub-Antarctic moth Pringleophaga marioni: Do caterpillars choose Wandering Albatross nest proxies?

On the South Indian Ocean Province Islands of the sub-Antarctic, most nutrients are processed through a detritus-based food web. On Marion Island, larvae of the moth Pringleophaga marioni are one of the key decomposers. Abundance of these caterpillars is higher in newly abandoned Wandering Albatross (Diomedea exulans) nests than other habitats, and this observation has been explained by hypotheses regarding the thermal and nutrient advantages of nests. These hypotheses require a mechanism for increasing the abundance of caterpillars, since nests are an ephemeral resource, and here, we determine whether caterpillars respond to chemosensory and thermal cues using a laboratory choice chamber approach. Caterpillars show no significant preference for newly abandoned nest material over no other choice, old nest material, and the common mire moss Sanionia uncinata. Caterpillars that are acclimated to warm (15 °C) conditions do prefer lower (5 °C) to higher (15 °C) temperatures, perhaps reflecting negative effects of prolonged exposure to warm temperatures on growth. Caterpillars also show significant avoidance of conspecifics, possibly because of incidental cannibalism previously reported in this species. Thus, we find no empirical support for nest-finding ability in caterpillars based on chemosensory or thermal cues. It is possible that adult females or very early instar caterpillars show such ability, or high caterpillar density and biomass in nests are an incidental consequence of better conditions in the nests or deposition by the birds during nest construction.     

Effects of temperature on the development and fecundity of Microplitis similis (Hymenoptera: Braconidae), a parasitoid of Spodoptera litura (Lepidoptera: Noctuidae)

Microplitis similis (Hymenoptera: Braconidae) is a solitary endoparasitoid of Spodoptera litura larvae (Lepidoptera: Noctuidae). Here, the effects of constant temperature (18, 21, 24, 27, 30, 33 and 36 °C) on the development and fecundity of M. similis developing in S. litura were studied in the laboratory to clarify the range of its potential distribution and better understand its potential as a biological control agent. The developmental duration of M. similis varied from 10.6 (33 °C) to 27.9 days (18 °C). The developmental threshold temperature and effective accumulative temperature of M. similis were 9.96 °C and 231.14 Degree-days, respectively. The average adult longevity of M. similis ranged from 5.1 (33 °C) to 26.8 days (18 °C). The maximum fecundity of the parasitoid was observed at 27 and 30 °C, which were 43.07 and 39.73 eggs, respectively. The minimum fecundity of the parasitoid was observed at 18 °C, which was 8.27 eggs. The intrinsic rate of increase (r_m) and finite rate of increase (λ) of M. similis were the highest at 30 °C. The net reproduction rate (R₀) was the highest at 27 °C and 30 °C, which were 44.34 and 40.39, respectively. We concluded that temperatures in the range 27–30 °C are the most suitable for development and reproduction of M. similis. Our study provides detailed basic information for development and reproduction of M. similis under different temperature conditions.     

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.     

Thermal sensitivity of cellular energy budgets in some Antarctic fish hepatocytes

Oxygen demand elicited by the main cellular energy consumers was examined in isolated hepatocytes of sub-Antarctic (Lepidonotothen larseni) and high-Antarctic notothenioids (Trematomus eulepidotus, Trematomus pennellii, Trematomus lepidorhinus, Trematomus bernacchii, Artedidraco orianae) and in a zoarcid (Pachycara brachycephalum) fish with respect to the role of cellular metabolism in co-defining thermal tolerance. The relative proportions of energy allocated to protein and RNA/DNA synthesis, ion regulation and ATP synthesis were quantified between 0°C and 15°C by analysis of inhibitor sensitive cellular respiration. In all the investigated species, protein synthesis constituted 25–37%, RNA synthesis 24–35%, Na⁺/K⁺-ATPase 40–45% and mitochondrial ATP synthesis 57–65% of total respiration. The sub-Antarctic nototheniid L. larseni displayed lower cellular protein synthesis rates but somewhat higher active ion regulation activities than its high-Antarctic confamilials, as is typical for more eurythermal species. Assumed thermal optima were mirrored in minimized overall cellular energy demand. In the sub-Antarctic L. larseni and P. brachycephalum, minima of oxygen consumption were located between 3°C and 6°C, indicating elevated energy turnover below and above these temperatures. In contrast, the high-Antarctic species displayed progressively rising respiration rates during warming with a cellular energetic minimum at 0°C. The sub-Antarctic nototheniid and the zoarcid showed signs of cold-eurythermy and appear to live close to their lower limit of thermal tolerance, while high-Antarctic notothenioids show high degrees of energetic efficiency at 0°C. All cellular preparations maintained energy budgets over a wide thermal range, supporting the recent concept that thermal limits are set by oxygen and associated energy limitations at the whole organism level.     

Low temperature mortality of the peach-potato aphid Myzus persicae

ABSTRACT.

• 1 The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min^?1 were ?26.6 and ?25.0°C respectively.
• 2 The LT₅₀ (temperature) of the same age groups drawn from the same population and cooled at the same rate were ?8.1 and ?6.9°C, indicating extensive pre-freeze mortality in M.persicae under laboratory conditions.
• 3 Acclimation at 10 and 5°C did not affect supercooling but depressed the LT₅₀ of both first instars and adult aphids.
• 4 Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature.
• 5 The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above.
• 6 The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important.
• 7 Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.

     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

Molecular and morphometric assessment of the taxonomic status of Ectemnorhinus weevil species (Coleoptera: Curculionidae, Entiminae) from the sub-Antarctic Prince Edward Islands

There are long‐standing controversies on the taxonomic status of Ectemnorhinus weevil species occurring on the sub‐Antarctic Prince Edward Islands. Since the two islands that constitute the Prince Edward Islands archipelago (PEIA), Marion Island (MI) and Prince Edward Island (PEI), differ in terms of alien invasive species such as the introduced house mouse Mus musculus and conservation management strategies, it is important to consider inter‐island dynamics when investigating inter‐specific relationships. Using a combined molecular phylogenetic and morphometric approach, we attempted to resolve the taxonomic status of the PEIA Ectemnorhinus weevil species. A COI gene phylogeny was inferred following the genetic characterization of 52 Ectemnorhinus weevils from both islands, and morphometric assessment using a set of 15 linear, external measurements was used to differentiate between the two currently recognized species, Ectemnorhinus similis and Ectemnorhinus marioni. Analyses revealed the presence of two genetically and morphometrically distinct species on PEI, whilst evidence for a single species, comprising diverse genetically discrete populations was found on MI. Based on these results, the species unique to PEI has been designated Ectemnorhinus kuscheli n. sp. whilst we confirm the synonymy between E. similis and E. marioni, the two species originally described from MI. E. kuscheli appears to be restricted to PEI, whereas E. similis occurs on both MI and PEI.     

Effects of extended and repeated exposures to low temperature on mortality of the peach-potato aphid Myzus persicae

Abstract.

• 1 The survival of adult and first-instar Myzus persicae reared at 20°C and 10°C was investigated after brief (1 min) exposure in the absence of plant material to temperatures between −5°C and −25°C, and extended exposures on plants of 1–10 days at a constant 5°C, 3°C and −5°C and a 24 h cycling regime between 5°C (18 h) and −5°C (6 h).
• 2 Life stage, rearing temperature, period of exposure and temperature regime all had a significant effect on the ability of aphids to survive cold. The effects of life stage and rearing temperature were most noticeable following exposure to cycling temperatures and extended exposures at −5°C, and least apparent after 1 min exposures at lower sub-zero temperatures.
• 3 Mortality following exposure to temperatures cycling between −5°C and 5°C was greater than that at 3°C (the mean of the cycling temperatures) and less than at a constant −5°C, suggesting that when temperatures fluctuate by a few degrees around 0°C the minimum temperature may affect survival to a greater extent than the mean.
• 4 These results suggest that an overwintering population of acclimated M.persicae would persist without significant mortality after a period of 7–10 days with −5°C frosts each night.

     

Temperature‐dependent development of the double‐spined spruce bark beetle Ips duplicatus (Sahlberg, 1836) (Coleoptera; Curculionidae)

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Effect of latitude and acclimation on the lethal temperatures of the peach‐potato aphid Myzus persicae

• 1 Aphids, similar to all insects, are ectothermic and, consequently, are greatly affected by environmental conditions. The peach potato aphid Myzus persicae (Sulzer) has a global distribution, although it is not known whether populations display regional adaptations to distinct climatic zones along its distribution and vary in their ability to withstand and acclimate to temperature extremes. In the present study, lethal temperatures were measured in nine anholocyclic clones of M. persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. The effects of collection origin and intra‐ and intergenerational acclimation on cold and heat tolerance, as determined by upper and lower lethal temperatures (ULT₅₀ and LLT₅₀, respectively), were investigated.
• 2 Lethal temperatures of M. persicae were shown to be plastic and could be altered after acclimation over just one generation. Lower lethal temperatures were significantly depressed in eight of nine clones after acclimation for one generation at 10°C (range: ?13.3 to ?16.2°C) and raised after acclimation at 25°C (range: ?10.7 to ?11.6°C) compared with constant 20°C (range: ?11.9 to ?12.9°C). Upper lethal temperatures were less plastic, although significantly increased after one generation at 25°C (range: 41.8–42.4°C) and in five of nine clones after acclimation at 10°C. There was no evidence of intergenerational acclimation over three generations.
• 3 Thermal tolerance ranges were expanded after acclimation at 10 and 25°C compared with constant 20°C, resulting in aphids reared at 10°C surviving over a temperature range that was approximately 2–6°C greater than those reared at 25°C.
• 4 There was no clear relationship between lethal temperatures and latitude. Large scale mixing of clones may occur across Europe, thus limiting local adaption in thermal tolerance. Clonal type, as identified by microsatellite analysis, did show a relationship with thermal tolerance, notably with Type O clones being the most thermal tolerant. Clonal types may respond independently to climate change, affecting the relative proportions of clones within populations, with consequent implications for biodiversity and agriculture.

     

Daily energy intake and growth of piscivorous brown trout,Salmo trutta

• 1 The chief objectives were to determine the daily energy intake and growth of piscivorous brown trout (Salmo trutta), and to compare the observed values with those expected from models developed previously for brown trout feeding on freshwater invertebrates. Energy budgets for individual fish were obtained from experiments with 40 trout (initial live weight 250–318 g) bred from wild parents, and kept at five constant temperatures (5, 10, 13, 15, 18 °C) and 100% oxygen saturation. Each trout was fed to satiation on freshly killed sticklebacks (Gasterosteus aculeatus) over a period of 42 days.
• 2 Energy intake (C_IN cal day^‐1) and growth (C_G cal day^‐1) were measured directly and energy losses (C_Q cal day^‐1) were estimated by difference (C_Q = C_IN ‐ C_G). All three variables increased with temperature. A model previously used to predict the daily energy intake (C_IN(INV)) of trout feeding to satiation on invertebrates was adapted, by changing only one parameter, to provide an excellent model (R² = 0.998) for predicting the mean daily energy intake (C_IN(ST)) for the piscivorous trout. Values of C_IN(ST) were 58% (range 48–67%) higher than those for C_IN(INV). A simple model was also developed to estimate mean daily energy losses for piscivorous trout (R² = 0.999). Both models were combined to provide excellent estimates of the daily energy gain (growth) of the piscivorous trout, and this was about three times that for trout feeding on invertebrates. The optimum temperature for maximum growth in energy terms increased from 13.9 °C for trout feeding on invertebrates to 17.0 °C (range 16.6–17.4 °C) for piscivorous trout.
• 3 The models are basically an extension of those developed for trout feeding on invertebrates. They show clearly how energy intake, growth, and the optimum temperature for growth increase markedly when trout change their diet from invertebrates to fish. The implications of this are discussed and it is shown that, in theory, these increases should continue if a more energy‐rich diet was utilised by the trout.

     

Estimated Impact of feral house mice on sub-Antarctic invertebrates at Marion Island

Summary The energy metabolism of feral house mice Mus musculus was established on sub-Antarctic Marion Island, using the doubly-labelled water turnover technique. Mean water influx was 565 ml kg^-1 day^-1 and mean CO₂ production was 5.41 ml g^-1 h^-1, i.e. 3375 kJ kg^-1 day^-1. From the energy content of the main items (Lepidoptera larvae, Curculionidae) in the diet of the mice it was estimated that the dry mass of food consumed was 3.5 g mouse^-1 day^-1. The overall impact of mice on invertebrates, based on mean mouse density and the mean percentage invertebrates in the diet, was estimated at 108 g ha^-1 day^-1 or 39.4 kg ha^-1 y^-1 (dry mass). Greatest predation pressure was on larvae of the flightless moth Pringleophaga marioni: 65 g ha^-1 day^-1 or 23.7 kg ha^-1 y^-1. Insect biomass is lower on Marion Island than on nearby Prince Edward Island, which is mouse-free. It is suggested that populations of certain insects on Marion Island are depressed by the alien mice.     

Temperature‐dependent development of the great European spruce bark beetle Dendroctonus micans (Kug.) (Coleoptera: Curculionidae: Scolytinae) and its predator Rhizophagus grandis Gyll. (Coleoptera: Monotomidae: Rhizophaginae)

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