Reproduction of Lumbricillus rivalis (Levinsen) in laboratory cultures and in decaying seaweed

The cocoon production of 144 Lumbricillus rivalis cultured in pairs at 10 ± 1 °C was high over the first 2 weeks of breeding activity and then declined, chiefly because of high mortality. Cocoon deposition lasted for between 1 and 16 weeks, eight pairs of worms producing cocoons for 9 weeks and one pair for 16 weeks. During the total period of cocoon deposition over 9000 eggs (mean 17·4 per cocoon) were deposited. Two decaying wrack bed populations of L. rivalis showed a low level of cocoon and egg production in autumn, rising to an annual maximum in late winter/early spring. In these populations the mean egg content varied seasonally from 17·1 to 47·8 eggs per cocoon. When cocoons in the laboratory were transferred from the site of deposition to incubation dishes 31% hatched, but those left in the substrate showed a 92% hatch. In the naturally occurring populations 19% of the cocoons detached from seaweed fronds hatched, but 62% of those left in situ. Eggs and worm embryos developed to relatively late stages in most cocoons, whatever the rate of hatching; development often continued for up to 2 months after deposition without hatching. Over 50% of the fertile eggs in cocoons from decaying wrack hatched and developed to 5 mm worms.     

Life cycle and food availability indices in Notiophilus biguttatus (Coleoptera, Carabidae)

Abstract.

• 1 Food demands of the predatory carabid Notiophilus biguttatus F. and their fulfilment were studied in the laboratory and field.
• 2 In the laboratory, larval consumption, growth, adult body size and egg production were established for different regimes of temperature and food, the springtail Orchesella cincta.
• 3 Temperature strongly influenced feeding rate of larvae and adults and consequently growth and oviposition rates. Accordingly, growth rate and ovi-position rate increased with prey supply.
• 4 Prey supply also had an effect on fat content, but the number of ripe eggs in the ovaries was related neither to temperature nor to prey supply.
• 5 Adult body size was affected by temperature during the larval period but more so by food supply.
• 6 Dissection of field fresh females showed them to bear eggs for the whole year, except in late winter/early spring and in July.
• 7 Fat content was low in spring and, from July on, high in summer and autumn. Survivorship during starvation differed widely between samples and seemed to be related to reproductive status rather than to fat content.
• 8 Samples of beetles and springtails from eleven pine plantations revealed for the beetles significant differences in fat content and body size, the latter ranging between the maximum and minimum value obtained in the laboratory.
• 9 Conclusions about food limitation based on body size and fat content were not corroborated by a relationship of these indices with springtail density.

     

Temperature‐dependent competition between juvenile salmonids in small streams

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Low temperature tolerance and starvation ability of the oak processionary moth: implications in a context of increasing epidemics

• 1 We investigated how modifications in winter and spring temperature conditions may affect the survival of a spring‐hatching Lepidoptera, the oak processionary moth Thaumetopoea processionea.
• 2 Supercooling and chilling injury experiments indicate that eggs are especially cold hardy at the start of the winter period, although this ability is reduced later in the season. In the spring, young larvae are sufficiently cold hardy to ensure no direct mortality as a result of late frosts.
• 3 A comparison of phenological models shows that neonate larvae may await the unfolding of new oak leaves for relatively long periods (e.g. 1–30 days). Under both low (4°C after 5 days at 16°C) and high temperature experimental scenarios (constant 16°C), the majority of neonate larvae can survive starvation for more than 2 weeks.
• 4 Larvae may also suffer from food depletion once their development has been initiated (e.g. during cold springs) if the threshold temperature for feeding is not reached for several consecutive days, or in the case of late frosts affecting foliage availability. When temperature is reduced to 4°C, developing larvae become inactive and do not feed anymore; their starvation survival capability is reduced to approximately 2 weeks (cold spring hypothesis). At 16°C, developing larvae that are deprived of food can only survive for 10 days (late frost hypothesis).
• 5 We conclude that, in the oak processionary moth, neonate larvae are relatively well adapted to early hatching relative to budburst, ensuring them the highest foliage quality for development. In some years, however, phenological asynchrony or cold spring conditions may affect the persistence of populations at the limits of the species' range.

     

An experimental study of ontogenetic and seasonal changes in the temperature preferences of unfed and fed brown trout,Salmo trutta

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Butterfly migration from and to peninsular Florida

Abstract.

• 1 Migrating butterflies were monitored with traps for 10 years at a site in north peninsular Florida, to determine seasonal and annual variation in numbers and directions of flight.
• 2 In the spring, 81–96% of the principal migrants, Phoebis sennae (L.), Agraulis vanillae (L.), Precis coenia (Hübner) and Urbanus proteits (L.), flew northward; in the autumn, 86–95% flew southward.
• 3 Estimated mean net numbers of these four species flying northward in spring across each ENE-WSW metre were 3, 6, 69 and <1 respectively; numbers flying southward in autumn were 222, 413, 37 and 146.
• 4 During a 5-year period, the ratio of highest to lowest seasonal migration for a species did not exceed 9.3.
• 5 The average median date of spring migration was 27 March for P.sennae, 23 April for P.coenia, and 12 May for A.vanillae. The average median date of autumn migration was 2–5 October except for U.proteus, whose average date was 14 October.
• 6 The autumn migratory period, as measured by the duration of the middle half of migration, was about 2 weeks in P.coenia and about 4 weeks in the other three species.
• 7 Compared to previously reported butterfly migrations, the ones studied here were notably uniform in magnitude and regular in timing.
• 8 These and other data suggest that 4 million or more of these butterflies migrate northward from peninsular Florida almost every spring and that 40 million or more migrate southward to peninsular Florida almost every autumn.

     

Are galling insects better protected against parasitoids than exposed feeders?: a test using tenthredinid sawflies

ABSTRACT.

• 1 Data mostly from the published literature were used to assess the effect of galling on the number of parasitoid species per host species in the phylogeny of nematine sawflies from free external feeders (colonial and solitary) to leaf gallers and shoot gallers.
• 2 The strongest effects of galling were the total elimination of the species-rich cocoon-attacking guild of parasitoids, and eonymphal parasitoids, from the parasitoid community on shoot gallers, all of which are in the genus Euura.
• 3 All tachinid larval parasitoids were also eliminated by the galling habit.
• 4 The cumulative effects of these exclusions resulted in a decline in mean number of parasitoid species per host species from almost sixteen species on external colonial feeders to 4.0 species on shoot gallers.
• 5 General patterns in per cent parasitism by non-tachinid and tachinid larval parasitoids, eonymphal and cocoon parasitoids, on exposed feeders to shoot gallers, showed declines in non-tachinid attack and elimination of tachinid, eonymphal and cocoon parasitoids. But leaf gallers tended to be attacked more than exposed feeders by non-tachinid larval parasitoids.
• 6 The galling habit had a long-term impact by reducing the number of parasitoid species attacking nematine sawfly gallers and per cent mortality inflicted, so that natural enemies may have been important as a selective factor in the evolution of galling nematine sawflies.

     

Is the Iberian lacewing Chrysopa regalis a semivoltine species?

ABSTRACT.

• 1 Adults of the lacewing Chrysopa regalis Navás were caught in north Spain, Huesca province, Aragon.
• 2 Their progeny reared in the laboratory under short- and long-day light conditions at 20°C, entered a long diapause as prepupae within the cocoon.
• 3 Transferred outdoors after spinning up, only a few (12%) became active again in the following spring, whereas the rest remained in diapause for one more year and waited for the end of the second spring to resume their morphogenetic development. Thus most of the studied strain exhibited a 2–year life cycle. This semivoltine strategy is new to chrysopid biology.
• 4 The predaceous larval phase did not exceed 3% of the total individual lifespan, though the duration of the free-living larval instars averaged 19.9±1.1 (SD) days.
• 5 During the extended diapause, weight loss was very small, no more than 6.6% of the initial weight, 16.9±2.7 (SD) mg, at the end of diapause, and 8.8% at the time of pupal ecdysis.

     

Population dynamics of brown trout (Salmo trutta) in Spruce Creek Pennsylvania: A quarter‐century perspective

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Will Environmental Stewardship enhance small mammal abundance on intensively managed farmland?

• 1 The creation of grassy field margins, as part of the UK Government's Environmental Stewardship (ES) scheme, is one of a number of measures proposed to mitigate the adverse effects of arable intensification on wildlife. Widespread development of these margins will potentially increase the amount of habitat available to small mammals in arable landscapes, as many species do not inhabit the cropped area.
• 2 The aim of this study was to determine what impact ES-type margins might have on small mammals. We compared small mammal abundance and biomass in spring and autumn on 3-m-wide and 6-m-wide grassy margins with that on conventionally managed field edges that have no margin (0 m wide) and are intensively cultivated to the field edge.
• 3 Bank voles Clethrionomys glareolus, wood mice Apodemus sylvaticus and common shrews Sorex araneus were the most abundant species; few field voles Microtus agrestis were captured on any margin. In autumn, bank vole and common shrew numbers were higher on the grassy margins than on conventional field edges, and margin width per se was positively associated with bank vole abundance. The number of wood mice captured did not differ among the different margin types.
• 4 Total small mammal biomass increased between spring and autumn on the 3-m- and 6-m-wide grassy margins, but decreased on the 0-m-wide margins. Total biomass in autumn was three times higher on 6-m-wide margins compared with the conventional arable field edges.

     

Previous infestation with Psammotettix alienus on spring wheat seedlings decreased the fitness of Sitobion avenae in a subsequent infestation

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Temporal changes in host adaptation in the pea aphid, Acyrthosiphon pisum

Abstract.

• 1 Temporal changes in host adaptation were followed in a local population of the pea aphid, Acyrthosiphon pisum. Aphid clones were collected in one alfalfa and one clover field at three different times. In the spring, first-generation females were collected. Later, in the autumn, females belonging to the last parthenogenetic generation were collected. Lastly, sexual females were collected after mating in autumn and allowed to produce eggs which were hatched. The performance was evaluated on alfalfa and clover. The spring-collected individuals were also assessed on peas.
• 2 On the overwintering hosts clover and alfalfa, the clones performed best on the plant of origin, i.e. negative correlations in performance. Correlations between performance on the temporary summer host, pea, and that on clover/alfalfa were weak or nonsignificant.
• 3 Significant variation in host performance was found within both host fields at spring, which is a prerequisite for changes in clone composition due to selection/migration.
• 4 The clones from alfalfa showed an increase in mean performance on alfalfa between spring and autumn, whereas no changes among the clones from the clover field were observed. This difference in seasonal response between the two fields could have been the result of larger variation in performance among the alfalfa clones and/or a differential tendency to migrate among clones in both fields.
• 5 After sexual recombination in the autumn, mean performance in the alfalfa field returned to the spring level, probably as a result of emergence of new genetic combinations. In the clover field, mean performance did not change significantly over time.

     

Winter warming effects on overwinter survival,energy use,and spring emergence of Cerotoma trifurcata (Coleoptera: Chrysomelidae)

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Mutual benefit interactions between banded pine weevil Pissodes castaneus and blue‐stain fungus Leptographium serpens in maritime pine

• 1 Ecological interactions between banded pine weevil Pissodes castaneus and blue‐stain fungus Leptographium serpens, when simultaneously sharing the same host plant (maritime pine Pinus pinaster) in winter and spring, were investigated. Temporal components of the interaction were taken into account by either introducing the weevils and the pathogen simultaneously or sequentially, with the weevils being introduced 1 month after the fungal inoculation.
• 2 We measured larval mortality, development time, offspring number, sex ratio and body size of P. castaneus. Phloem phosphorus and nitrogen concentrations were also assessed. Furthermore, we tested whether: (i) emerging offspring transported propagules of the fungus; (ii) artificially‐contaminated weevils may transmit the disease to healthy trees; and (iii) field collected P. castaneus carry the fungus.
• 3 The fungus enhanced weevil colonization and brood production in both seasons. During winter and spring, adults from trees where the pathogen was inoculated prior to weevil introduction emerged earlier than weevils from trees where they had been introduced simultaneously with the fungus. During winter, weevils from pre‐inoculated trees were also larger. Sex ratio and larval mortality were not affected. Leptographium serpens did not affect phloem nitrogen content but phosphorus content was greater in plants inoculated with the pathogen, which may explain the findings on weevil growth.
• 4 Sixty‐five percent of the weevils that emerged from inoculated trees carried spores of L. serpens, although no successful isolation was made from field collected weevils. The fungus was recovered from 25% of the trees infested with artificially‐contaminated weevils.
• 5 These results suggest that P. castaneus benefits from the presence of L. serpens and may contribute to its spread.

     

Calibration of FST-hemispheres against bottom shear stress in a laboratory flume*

SUMMARY.

• 1 Fliesswasserstammtisch (FST)-hemispheres of identical size but different densities were exposed on a horizontal plane on the pebble-covered bottom of a laboratory flume at streaming to shooting, turbulent and fully developed flow. The heaviest hemisphere moved was used as an indicator of shear stress, a flow force acting on the flume bottom.
• 2 The relationship between shear stress and hemisphere density was practically the same for three different sets of hemispheres, namely one prototype set newly prepared for the calibrations, one prototype set intensively used in the field prior to calibrations, and one randomly selected new set bought commercially.
• 3 Shear stress (y, dyn cm^?2) was related to hemisphere density (x, g cm^?3) by y= x^2.85 (n= 69; r²= 0.993). For lighter hemispheres this relationship was better explained by the linear model y= 7.32x– 6.60 (n= 35; r²=0.983).

     

Egg-laying by the speckled wood butterfly (Pararge aegeria): the role of female behaviour, host plant abundance and temperature

ABSTRACT.

• 1 Egg-laying by Pararge aegeria (L.) was studied in relation to host plant abundance, temperature and behaviour in one woodland site in central England.
• 2 Eggs were laid on the undersides of leaves of fifteen of thirty-one species of grass located in the study site. Most were deposited singly although on several occasions a number of females laid on a single leaf.
• 3 There was no clear relationship between host plant abundance and host plant use, the species used being widespread and abundant.
• 4 Most eggs were laid on plants within the temperature range 24–30°C. In spring and later summer these sites were in sunlit open areas but in midsummer they were in the woodland ground layer.
• 5 Females distributed their eggs over a large area, usually making a dispersal flight after laying an egg.

     

Parasitoid genus‐specific manipulation of orb‐web host spiders (Araneae,Araneidae)

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Causes of Daphnia midsummer decline in two deep meromictic subalpine lakes

1. Daphnia are key organisms in pelagic food webs, acting as a food resource for fish and predatory zooplankton and regulating phytoplankton through grazing. Its population dynamic follows regular seasonal patterns, with spring peaks followed by summer population declines (midsummer declines, MSDs). Midsummer declines show high inter-annual variation, which has been attributed to different causes. However, the mechanisms controlling the MSD remain poorly understood, especially in deep stratified lakes.
2. We tried to disentangle the factors causing Daphnia MSDs in Lake Lugano and Lake Iseo (in Switzerland and Italy), two deep peri-alpine lakes with similar trophic status and vertical mixing dynamics, characterised by phosphorus accumulation in the hypolimnion and variable mixing during late-winter turnovers.
3. Specifically, we assessed the effects of three different hypothetical pathways according to which: (1) winter air temperature controls MSDs by influencing mixing depth during turnovers and epilimnetic phosphorus replenishment; (2) vernal air temperature influences MSD by accelerating the timing of spring population peak; and (3) summer temperature influences MSDs by increasing fish predation. We assessed the relative strength of these pathways using structural equation modelling on long-term datasets for the two lakes (29 years for Lake Lugano and 19 years for Lake Iseo).
4. Between the hypothesised pathways, the one driven by winter air temperature (through P replenishment) influenced Daphnia abundance in spring in both lakes, but the effects propagated to summer Daphnia abundance only in Lake Lugano. Additionally, summer Daphnia abundance was influenced by the summer air temperature through a positive (although weak) effect. By comparison, vernal air temperature had no detectable effects on summer Daphnia abundance.
5. The results revealed marked differences between the meromictic study lakes and the shallow hypertrophic water bodies that were the focus of previous research on Daphnia MSD, and also between the two study lakes. The influence of epilimnetic P replenishment on the summer Daphnia abundance in Lake Lugano, which was recovering from past eutrophication, may have reflected the greater susceptibility of deep, stratified lakes to P depletion after spring compared to shallow hypertrophic lakes or reservoirs. This effect might not have been detected in Lake Iseo because P was more consistently depleted during the study period (i.e. variance in the predictor was too low to detect an effect).
6. This study highlighted the complexity of the effects of climate variability on Daphnia MSD in deep lakes, showing that the responses can differ even between two neighbouring lakes with similar vertical mixing dynamics and trophic status. At the same time, the results suggest that future increases in winter air temperature, caused by global warming, may cause critically low densities of Daphnia during spring and summer and compromise the ability of zooplankton to control phytoplankton biomass.

     

Adenylate energy charge in streambed sediments

SUMMARY.

• 1 The adenylate energy charge (EC_A) of microbial communities from streambed sediments was measured during three different seasons, under experimental manipulation and in culture.
• 2 The EC_A values of sediments (x±S.E.) in the autumn, winter and spring were low and constant; 0.22±0.03 (n=12), 0.32±0.04 (n= 12) and 0.28±0.03 (n=6) respectively.
• 3 A 5 h exposure of sediments to an algal lysate at 3.0–4.0°C and a 48 h exposure of sediments to tryptone-yeast extract at 8.0–18.0°C failed to increase EC_A even though respiration increased 3.7-fold during the latter exposure.
• 4 The cellular EC_A of a bacterial monoculture, sampled in log phase, was 0.90±0.10 (n=3), but cxtracclluhir AMP depressed the total culture EC_A to 0.21±0.01 (n=4).
• 5 Attempts to isolate extracellular AMP from the interstitial waters of sediments were unsuccessful.
• 6 The data suggest that under natural conditions EC_A is of limited use as a monitor of subtle changes in the physiological state of microbial communities in streambed sediments.