Accumulation and egestion of dietary copper and cadmium by the grasshopper Locusta migratoria R & F (Orthoptera: Acrididae).

Copper and cadmium budgets were studied for a model insect herbivore/host plant system comprising the oligophagous leaf-chewing grasshopper (Locusta migratoria) feeding on Zea mays (Gramineae). Fifth instar larvae were fed, for between 5 and 20 days, on maize foliage contaminated with either copper, cadmium or on control foliage containing no excess metal. Male and female locusts fed on copper-treated maize retained 45 and 42% of ingested copper respectively, figures not significantly different from the 41 and 33% retained on untreated maize. Remaining copper was egested with the faeces. Locusts fed on copper-treated maize showed an increase of 27% in body copper burden compared with those on the control diet: the increase was independent of time on the diet. Female locusts retained 33% and males 21% of ingested cadmium. Faecal cadmium levels were elevated, and accumulation in both sexes was proportional to time on the Cd-enriched diet. For both copper and cadmium, some ingested metal probably passed directly through the locust gut, bound to undigested food material. Results suggest that grasshoppers may effectively regulate excess dietary copper, but are unable efficiently to regulate cadmium.

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.

The effects of feeding by the black bean aphidAphis fabae Scop. (Homoptera: Aphididae) on copper and cadmium accumulation in broad bean (Vicia faba L.).

Broad beans (Vicia faba L.), cultured hydroponically were supplied with 100 µg mL(-1) copper or 50 µg mL(-1) cadmium in nutrient solution. Samples of plant material from both nutrient regimes were analysed before and after infestation by the black bean aphid (Aphis fabae Scop.). Heavy aphid infestation resulted in a significant reduction in copper content of shoots in comparison with uninfested plants. A similar, but less well- defined, situation occurred in the case of cadmium.Further investigations examined the effects of different levels of aphid infestation on the above phenomena. In all cases the presence of feeding aphids reduced elemental accumulation in plant shoots. Long term infestation with population densities as low as three adult aphids showed a reduction in shoot copper and cadmium content.

The distribution, abundance and host plant relationships of Salix- feeding psyllids (Homoptera: Psylloidea) in arctic Alaska.

1. Five species of psyllid occurred on seven species of Salix at Meade River, Alaska. Studies were made on the two common species Psylla pclmeni Löw and P.phlebophyllae Hodkinson. The former feeds on the phanerophy tes Salix pulchra, S.lanata, S.alaxensis and S.glauca, the latter on the chamaephytes S.phlebophylla and S.reticulata. 2. Both P.palmeni and P.phlebophyllae had a 1-year life cycle and nymphal development took place on the female Salix catkin. The life cycle was generally closely synchronized with the period of catkin development. However, only a few eggs were laid on S.glauca 3. Seasonal perturbation of the host plant by flooding, ice movement and blown sand prevented psyllids breeding in certain areas colonized by the host plant. 4. In P.palmenidensities and 'feeding pressure', measured as biomass of psyllids per gram of catkin, on the different host plants followed the sequence S.pulchra>S.lanata> S.alaxensis > S.glauca. In P.phlebophyllae densities and feeding intensities were similar onS.phlebophyllaandS.reticulataand grazing intensity was comparable withP.palmenion S.pulchra. 5. A highly significant negative correlation was found between psyllid density and catkin dry weight in S.pulchra, S.phlebophylla and S.reticulata, suggesting that psyllid feeding is affecting catkin growth. 6. Predation of psyllid nymphs by syrphid larvae was heavy but there was no evidence of parasitism. 7. The life history strategies of the five psyllid species are discussed within the context of the constraints imposed by the arctic environment.

Energy flow and organic matter decomposition in an abandoned beaver pond ecosystem.

A beaver pond can be considered an open ecosystem with a number of energy inputs and outputs. The net difference between input and output represents the accumulation of energy within the system. During 1973 input-output parameters were measured independently for one spring fed pond (surface area 736 m2) in the Kananaskis Valley, Alberta, Canada. The yearly energy budged indicated that allochthonous energy inputs into the pond were much greater than autochthonous inputs. Of the total yearly energy input 18% was exported, 26% was respired and 56% accumulated in the sediments. This percentage utilization for respiration was low when compared with similar data from the literature for live aquatic ecosystems elsewhere. However the actual annual mean sediment respiration rate of 8.4 ml m-1 hr-1 compared favourably with the figure of 6.1 ml m-2 hr-1 predicted from Hargrave's 1969 respiration equation for benthic communities. This situation suggests that the allochthonous input, while dominant, is highly refractive and rapidly becomes locked up in the sediments. The high photosynthesis-respiration ratio of 0.81 together with the results of earlier litter bag experiments (Hodkinson, 1975) support this conclusion. Thus the beaver pond is a highly accretive heterotrophic ecosystem.