I. D. Hodkinson

Life cycle variation and adaptation in jumping plant lice (Insecta: Hemiptera: Psylloidea): a global synthesis

This paper integrates the scattered information on the life histories of the jumping plant lice or psyllids, examining those aspects of their biology that contribute to successful life cycle completion. Variation in life history parameters is reviewed across the worlds psyllids and the relative importance of phylogeny and environment, including host‐plant growth strategy, in determining life history strategies is assessed. Elements of life cycles considered include: development rate and voltinism, response to high temperature and drought, cold‐hardiness and overwintering strategy, seasonal polymorphism, diapause, metabolism, host‐plant selection and range, phenological and other adaptations to host plants, disease transmission and host amelioration, dispersal, reproduction and mate finding. Life history parameters are analyzed for 342 species. While a phylogenetic signal can be identified within the data, the main drivers for life history adaptation are environmental temperatures and water availability, acting directly on the psyllids or mediated through their host plants.

Effects of experimental temperature elevation on high-arctic soil microarthropod populations

An experiment was conducted to measure the effects of summer warming on the total population densities of soil-dwelling microarthropods in the high Arctic and to compare these results with those from natural between-year and between-site variations. Small polythene tents were used to elevate summer temperatures over 3 years on polar semi-desert and tundra heath in West Spitsbergen, Svalbard, Norway. Soil cores were taken at regular intervals from tented and untented (control) plots and heat extracted for mites (Acarina: Oribatida) and springtails (Collembola). Species present were similar at both sites, but at the start of the experiment total springtail populations were greater at the polar semi-desert whilst oribatid mite densities were equal at both sites. No significant effect of temperature elevation on oribatid mite populations emerged, even after 3 years. By contrast, springtail numbers were significantly lower on tented versus control plots at the polar semi-desert at the end of year 3, but not so at the tundra heath. Collembola numbers declined at both sites during the warm dry midsummers of 1992/1993 and this was most marked at the better drained polar semi-desert site. Over the equivalent period total oribatid mite populations, while relatively more stable, increased significantly at the polar semi-desert as a result of an increase in the number of juveniles. Results are interpreted in the context of the ecophysiological adaptations of oribatid mites and springtails to soil temperature and moisture. The resulting survival characteristics are considered in relation to the temperature and moisture characteristics of the two sites. The experiment demonstrated that year to year variation in climate, interacting with physical differences between sites, produced an equal or greater effect on microarthropod numbers at any one site than the 8–10% increase in “heat availability” (day degrees above zero) resulting from the summer tent treatment. The limitations of the use of tents to elevate soil temperatures are discussed. Comparisons are made with microarthropod population data from other polar and alpine sites.

Simulated climate change: The interaction between vegetation type and microhabitat temperatures at Ny Alesund, Svalbard

Small polythene tents were used to simulate the effects of climate warming on two contrasting vegetation types (polar semi-desert and tundra heath) at Ny Ålesund, Spitzbergen, Svalbard. Temperature microclimates are compared within and without tents and between sites with contrasting vegetation types. Summer temperatures were increased by about 5°C in the vegetation mat and by about 2°C in the soil at 3 cm depth. Cumulative day degrees above zero were enhanced by around 35% in the vegetation and by around 9% in the soil. Soil temperatures were greatly influenced by the nature of the overlying vegetation, which at one of the sites appeared to act as an efficient thermal insulator, preventing heat conductance into the soil from above and enhancing thermal contact between the upper soil layer and the cooling permafrost below. The significance of the observed temperature differences for the ecology of the plants and invertebrates is discussed.

Can high Arctic soil microarthropods survive eleveated summer temperatures

1. Tolerance of high summer temperatures was investigated in seven common species of oribatid mite (Acarina) and springtail (Collembola) found in soils associated with dominant vegetation types in West Spitsbergen, Svalbard. 2. Laboratory survival experiments are linked with field data from a 3-year temperature manipulation experiment to characterize the response of these animals to elevated field temperatures. 3. A 1-h exposure to 30⚬C under moist conditions showed that none of the species studied suffered significant mortality. The temperature required to kill all individuals was between 35-40 and 40-45⚬C for springtails and mites respectively. Under dry conditions at equivalent temperatures, differences in survival between mites and Collembola were strongly accentuated. Oribatid mites were little affected by the additional drought stress but the lethal temperature for springtails was shifted downwards by several degrees. 4. In parallel 3-h exposure experiments under moist conditions, the thermal death point was shifted downwards by c. 2.5⚬C in all the species, compared with 1-h exposures. Under dry conditions most Collembola died but mite survival differed little from that in the corresponding wet treatment over 3 h. 5. In longer-term experiments some mature Onychiurus arcticus survived more than 196 and 68 days at 5 and 25⚬C respectively. Above 30⚬C individuals survived for <24 h. 6. Regression relationships were established between maximum microhabitat temperatures and screen temperatures over 3 years. These were used to predict past maximum vegetation/litter mat and soil temperatures from historical screen data and to estimate the screen temperatures necessary to raise microhabitat temperatures to the thermal death point of the soil-dwelling arthropods. 7. The results are used to interpret the findings of a 3-year field experiment which examined the response of mite and springtail populations to temperature enhancement on two tundra sites, using small polythene tents. 8. High Arctic soil microarthropods appear able to cope with the higher summer temperatures they may experience as a result of climate change. It is the associated changes in soil moisture status that will probably produce the more significant changes in the microarthropod community. Species differ in their susceptibilities, but a decrease in soil moisture appears to favour oribatid mites at the expense of Collembola.

Effects of temperature elevation on a field population of Acyrthosiphon svalbardicum (Hemiptera: Aphididae) on Spitsbergen

A manipulation experiment was carried out on a field population of the aphid Acyrthosiphon svalbardicum near Ny Ålesund, on the high arctic island of Spitsbergen, using cloches to raise temperature. An average rise in temperature of 2.8 deg. C over the summer season markedly advanced the phenology of both the host plant Dryas octopetala and the aphid. Advanced aphid phenology, with concomitant increases in reproductive output and survival, and successful completion of the life-cycle led to an eleven-fold increase in the number of overwintering eggs. Thermal budget requirements in day degrees above 0°C were calculated for key life-cycle stages of the aphid. Temperature data from Ny Ålesund over the past 23 years were used to calculate thermal budgets for the field site over the same period and these were compared with the requirements of the aphid. Each estimated thermal budget was then adjusted to simulate the effect of a +2, +4, and −2deg. C change in average temperature on aphid performance. This retrospective analysis (i) confirms that the life-cycle of A. svalbardicum is well suited to exploit higher summer temperatures, (ii) indicates that the annual success of local populations are sensitive to small changes in temperature and (iii) suggests that the aphid is living at the limits of its thermal range at Ny Ålesund based on its summer thermal budget requirements.

Progressive restriction of host plant exploitation along a climatic gradient: the willow psyllid Cacopsylla groenlandica in Greenland

1. Host plant selection by the endemic willow psyllid Cacopsylla groenlandica was studied at eight sites in three locations along a N–S climatic gradient in west Greenland.

Thermal adaptation in the Arctic collembolan Onychiurus arcticus (Tullberg)

Ecophysiological characteristics, including survival at high and low temperatures, locomotory activity at sub-zero temperatures, supercooling ability and oxygen consumption rates, were investigated for the Arctic springtail Onychiurus arcticus (Tullberg) (Collembola, Onychiuridae). Individuals had a mean (± SE) fresh weight of 428.2±107.6 μg which contained 74.0±10.2% body water. Survival at high temperatures was humidity dependent. After 3h exposure at 100% relative humidity and 30°C, >80% of the animals survived, but at >32.5°C no individual survived. 70% of the animals survived a 1 h exposure at 32.5°C but at 35.0°C all animals died. At 0% relative humidity there were no survivors after 3 h at >25.0°C. At sub-zero temperatures, 60% of the springtails survived for 84 days at −3.0°C, but at −5.0°C survival was reduced to 35%. Individual collembolans showed locomotor activity down to −4°C. O. arcticus was freezing-intolerant and individuals supercooled to −6.1±0.1°C before freezing. This relatively high mean (±SE) supercooling point was stable throughout summer and was unaffected by acclimation temperature. A non-linear relationship existed between oxygen consumption and temperature. Between 0 and 10°C the Q10 was high at 7.0. It declined to 1.6 over the temperature range 10 to 30°C, increasing to 5.8 at higher temperatures. O. arcticus possesses ecophysiological characteristics suited to life in the upper layer of soil and surface vegetation, and beneath snow cover. However, it appears to be poorly adapted to survive severe winter temperatures being intolerant of freezing and with little supercooling ability. Such features may restrict its present distribution in the Arctic, but it seems likely that it would benefit by an increase in environmental temperature.

Extreme adaptive life-cycle in a high arctic aphid, Acyrthosiphon svalbardicum

Abstract. 1 The year‐round biology of a high arctic aphid is described for the first time. 2 The life‐cycle is shown to be genetically determined, and thus markedly different to temperate species where the observed polymorphism is governed primarily by external environmental cues. 3 The fundatrix, which emerges from the overwintering egg, gives birth directly to sexual morphs, a phenomenon previously undescribed in the Aphidinae. This process is essentially prevented in temperate aphids by an endogenous mechanism, the interval timer. 4 In addition to the sexual morphs, the fundatrix produces a small number of parthenogenetic individuals (viviparae) that give rise to a third generation. This last generation consists exclusively of oviparae and males that would increase the number of overwintering eggs provided there is sufficient thermal budget for them to mature and oviposit before conditions become adverse. 5 The position of particular morphs in the birth sequences of the second and third generations maximize the chances of survival in harsh conditions, whilst enhancing the likelihood that individuals from the third generation will add to the number of overwintering eggs. 6 Guaranteed egg production combined with an in‐built flexibility to produce an extra generation in particularly favourable seasons, confer adaptations to the high arctic environment, and ideally suit this aphid to exploit elevated temperatures in an era of climate change.

The psyllids (Homoptera: Psylloidea) of the Oriental zoogeographical Region: an annotated check-list

The 357 species of jumping plant lice (Homoptera: Psylloidea) recorded from the Oriental zoogeographical realm, including the whole of mainland China, are listed under their respective genera. Information is given on synonymy, host-plants and distribution. The position of problematical taxa is discussed. The check list is supplemented by a taxonomic list of host-plants and their associated psyllids and by a resume of published descriptions of undetermined psyllid galls.

Low summer temperatures: a potential mortality factor for high arctic soil microarthropods?

Throughout the summers of 1992–1994 the low temperature performance of soil microarthropods at Ny Alesund, Spitsbergen (78 °56′N 10 °53′E), was investigated. Species studied were the Collembola Hypogastrura tullbergi (Schaffer), Onychiurus arcticus (Tullberg) and Onychiurus groenlandicus (Tullberg) and the mites Diapterobates notatus (Thorell), Hermannia reticulata (Thorell), Camisia anomia Colloff and Ceratoppia hoeli (Thor). The results show that: (i) The supercooling ability of these animals decreased rapidly on regaining activity in spring. For example, the supercooling point (scp) of H. tullbergi when heat extracted from frozen ground, decreased from −20 to −8 °C within 4 h. Population scp profiles of all species determined throughout the summer showed distinct bimodal distribution; (ii) starvation for 14 days, desiccation or a combination of both, resulted in little change in the mean scp of the collembolan O. arcticus; (iii) survival of the animals after a brief exposure to a sub-zero temperature was poor, in either humid or dry atmospheres. For example, 77% of H. tullbergi died after cooling to −5 °C at 1 °C min−1. Comparison with scp data indicates that animals died before they froze; (iv) all species examined showed some locomotory ability at temperatures approaching −3 °C; (v) polyols occurred in low concentrations, although elevated levels of glucose were observed in early spring and late autumn in O. arcticus; and (vi) soil temperature declined to −29.6 °C in the winter of 1992/93 and remained below zero for up to 289 days and the animals can be encased in ice for 75% of the year. Average daily soil temperatures for July and August rarely exceed 8 °C and were typically in the range 3–6 °C. Estimation of previous years soil temperatures from screen temperature records indicate that July /August ground surface temperatures < 0 °C occurred on 25 and 28 occasions between 1969–1993 at the polar semi-desert and tundra heath sites respectively; but, that soil temperatures at a depth of 3 cm are buffered against temperature extremes and temperatures below 0 °C are rarely encountered. The consequences for the soil microarthropod fauna of such extended periods of low temperature and the effects of climate change on these species are discussed.