The influence of the rate of temperature change on the activation of dormant seeds of Rumex obtusifolius L.

1. One temperature shift from 20 to 30°C in darkness induces 30–40% germination in Rumex obtusifolius seeds. The same germination percentages are found with heat treatment varying between 1 and 6h duration, indicating that the total heat sum of the temperature shift is not important.
2. Germination is greatly enhanced by three consecutive heat shifts of 1h at 30°C separated by 1h periods at 20°C.
3. The seeds are activated to a small extent after a slow warming (+2°Ch^–1) from 20 to 30°C, followed by incubation for 1h at 30°C. Germination is much higher after rapid heating (+10°Ch^–1) to 30°C, followed by 1h incubation at this temperature. Repeated fast heating treatments on four consecutive days enhances germination. Moderately rapid heatings (+3·3°Ch^–1) give intermediate results.
4. The rate of cooling does not influence the germination percentage. Cooling alone cannot induce germination.
5. Heating alone from 15 to 25°C without cooling also activates germination. In this temperature range the seeds are more activated by rapid warming than by slow warming.
6. The ecological relevance of the response to different warming rate is discussed. The insensitivity of seeds to a slow warming might keep deeply buried seeds in a dormant stage.     

Can a community of small-bodied grazers control phytoplankton in rivers?

1. Phytoplankton, zooplankton and grazing were monitored throughout the growing season for three years (1994–96) in the Belgian section of the River Meuse.
2. A size structure analysis of the algal community shows that there was a summer shift toward larger algal units, following a decline in phytoplankton biomass. These changes occurred after an increase in zooplankton biomass and diversity.
3. Daily filtration rates of grazers ranged from 1 to 113% day^–1 and maxima were observed during the summer period. Higher rates tended to correspond with peaks of rotifer biomass. A decline in total phytoplankton biomass within two weeks followed the increase in zooplankton biomass and filtration rate. A rapid biomass recovery was then observed, along with a shift of the algal community toward larger units. When grazing activity was not sustained, due to zooplankton fluctuations, the change in phytoplankton size structure was less marked.
4. We suggest that the composition of the phytoplankton community of large rivers may at times be controlled by grazers. However, such biotic interactions can take place only when physical constraints are reduced, i.e. when discharge is low, and when increased transfer time, high temperature and availability of grazeable algae allow high zooplankton biomass.     

Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [³H] thymidine and [¹⁴C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l^–1 day^–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.
2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell^–1 day^–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.
3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h^–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.
4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.     

Seasonal pattern in nutrient limitation and grazing control of the phytoplankton community in a non-stratified lake

1. The relative importance of zooplankton grazing and nutrient limitation in regulating the phytoplankton community in the non-stratified Lake Kvie, Denmark, were measured nine times during the growing season.
2. Natural phytoplankton assemblage bioassays showed increasing importance of nutrient limitation during summer. Growth rates at ambient nutrient concentrations were continually below 0.12 per day, while co-enrichment with nitrogen (N) and phosphorus (P) to above concentration-saturated conditions enhanced growth rates from May to the end of July.
3. Stoichiometric ratios of important elements in seston (C : N, C : P, N : P), in lake water (TN : TP), in external loading (TN : TP) and in internal loading (DIN : DIP) were measured to determine whether N or P could be the limiting nutrient. TN : TP molar ratio of both lake water, benthic fluxes and external loading suggested P limitation throughout the growing season. However, seston molar ratios suggested moderate P-deficiency only during mid-summer.
4. Abundance and community structure of the zooplankton varied considerably through the season and proved to be important in determining the responses of algal assemblages to grazing. High abundance of cladocerans and rotifers resulted in significant grazing impact, while cyclopoid copepods had no significant effect on the phytoplankton biomass.
5. Regeneration of ammonium and phosphate by zooplankton were periodically important for phytoplankton growth. A comparison of nutrient regeneration by zooplankton with nutrient inputs from sediment and external sources indicated that zooplankton may contribute significantly in supplying N and P for the growth of phytoplankton.     

Population dynamics and production of five crustacean zooplankters in a subtropical reservoir during years of contrasting turbidity

SUMMARY 1. The temporal dynamics and demography of Meta-diaptomus meridianus (Van Douwe), Lovenula excellens Kiefer. Daphnia gibba Methuen, D. barbata Weltner and Moina brachiata Jurine were studied for 2 years in a small bay of Lake le Roux (Orange River, South Africa). Total zooplankton biomass and population density were 1.4–3 times higher during the less turbid conditions of 1982/83 (Secchi depth transparency around 35 cm) than they were at around 25 cm Secchi depth during 1981/82, when D. barbata was absent.
2. On average, instantaneous birth rates, rates of population change and death rates varied only slightly between years. Birth and death rates were considerably higher above 15°C than below 15°C. These rates correlated with one another and with zooplankton abundance both inter- and intra-specifically suggesting that competitive interactions were important in population regulation. Mortality rates varied more strongly and consistently in a density-dependent direction than did birth rates. In addition to depressed fecundity, the inferred survival of young was poor and population growth low, possibly because food shortage caused high post-natal mortality.
3. Estimates of annual production derived from finite birth rate values varied consistently with annual differences in biomass, and amounted to between 6 and 10 g m⁻² y⁻¹ dry wt. Annual P/B values varied from around 20 for the daphnids to 55 for the copepods and 75 for Moina. Apart from the latter, whose annual P/B ratio virtually doubled from 45 to 75 following reductions in turbidity, annual differences in P/B ratio were slight.     

Hatching of cladoceran resting eggs: temperature and photoperiod

Summary 1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages.
2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 °C. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination.
3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species.
4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 °C should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n  = 100) can be selected from the total hatchling assemblage.     

Interspecific and intraspecific variations in egg hatching for British populations of the stoneflies Siphonoperla torrentium and Chloroperia tripunctata (Plecoptera: Chloroperiidae)

SUMMARY 1. The objective was to compare variations in egg hatching between the two species (interspecific variations) and between populations of the same species (intraspecific variations). There were significant interspecific, but not intraspecific, differences in female size, adult life-span, egg production, hatching success, incubation periods and hatching periods.
2. The optimum temperature for hatching success within the range 3.8–22.1°C in the laboratory and the range over which at least 50% of the eggs hatched were lower for Chloroperia tripunctata (Scopoli) (8.5°C, 4.2–17.3°C) than for Siphonoperla torrentium (Pictet) (12.8°C, 6.1–19.4°C). Few eggs hatched at 22.r°C.
3. The relationship between incubation period (d days) and water temperature (T°C) was given by: d=1219/T^1.368 for S. torrentium , d=253/T^0.459 for C. tripunctata . Both equations successfully predicted incubation periods for eggs placed in a stream. The period over which eggs hatched was much longer for C. tripunctata than for S. torrentium at all temperatures.
4. The shorter incubation period (at r>5.6°C) and shorter hatching period for S. torrentium ensure that larvae of this species are already growing when eggs of C. tripunctata start to hatch, but the prolonged hatching period of the latter species ensures a long period of larval recruitment to the population. These differences in egg hatching may reduce competition between the two closely-related species.     

Implications of Chaoborus pupation and ecdysis in cold water

1. Cold water acted differently to delay and lengthen the pupation period for the larvae of two species of the zooplankton predator Chaoborus (Diptera: Chaoboridae). During Chaoborus pupation, the zooplankton community is released from predation, while the dark-coloured Chaoborus pupae are more susceptible to their own predators.
2. Fourth instar larvae of Chaoborus americanus and C. trivittatus , collected from an oligotrophic lake, were reared individually at 5 °C in the dark. Chaoborus americanus was also reared at 9 and 12 °C under spring photoperiod conditions (L : D, 16 : 8 h). Individuals were observed through pupation to emergence (ecdysis) or death.
3.  Chaoborus americanus pupated at 5, 9 and 12 °C with substantial emergence only at 12 °C. In comparison, C. trivittatus emerged at 5 °C. Light was not a necessary cue for pupation and ecdysis, contrary to previous reports. Cold water delayed the onset and lengthened and increased the variability of the duration of pupation.
4. In Shirley Lake, C. americanus pupated in late June–early July while C. trivittatus pupated first in April and again in June–July.
5.  Chaoborus americanus pupae needed a temperature cue to complete ecdysis. The ecdysis temperature threshold helps to explain the difference in pupation timing, and the geographical distribution, of C. americanus and its relatively inflexible life history contrasted with C. trivittatus . Delayed predator pupation in years with low spring temperature can affect the community dynamics of the prey.     

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.     

Natural thermal stress and heat-shock protein expression in Drosophila larvae and pupae

1. Whether Drosophila larvae and pupae naturally experience temperatures that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat-shock response in Drosophila . Accordingly, the temperatures of necrotic fruit, which Drosophila larvae and pupae inhabit, the temperatures of larvae and pupae outside the laboratory, and the levels of the heat-shock protein hsp 70 expressed by larvae in nature were examined.
2. When necrotic fruit was sunlit, internal temperatures rose to levels that can harm indwelling insects. Fruit size and evaporative water loss affected these temperatures. Temperatures of larvae and pupae in the field commonly exceeded 35 °C, with living larvae recorded at >44°C and pupae at >41°C. Natural mortality was evident, presumably because of heat.
3. In the laboratory, these temperatures kill larvae rapidly, with LT₅₀s (time taken for half the sample to be killed) of 30 min at 39 °C, 15 min at 40 °C and 8·5 min at 41 °C. Gradual transfer from 25°C to these temperatures resulted in no lesser mortality than did direct transfer.
4. Hsp 70 levels in lysates of whole larvae were measured by ELISA (enzyme-link immunosorbent assay) with an hsp 70-specific antibody. For larvae within necrotic apples experimentally transferred from shade to sun and within necrotic fruit in situ , hsp 70 levels equalled or exceeded levels detected in parallel laboratory studies of whole larvae or cells in culture.
5. These data provide an ecological context for studies of thermal stress and the heat-shock response in Drosophila that has heretofore been lacking.     

Diapause in twenty-three populations of Plodia interpunctella (Hübner) (Lep., Pyralidae) from different parts of the world

Abstract. 1. The incidence of diapause in twenty-three populations of Plodia interpunctella from fifteen countries representing all continents of the world was examined. The origins of populations varied from 52°N to 35°S and included two from equatorial regions.
2. Diapause occurred in all population samples at 20°C in short photoperiods (LD 11:13) and in continuous light, although the proportion of larvae doing so was less than 25% in samples from the equatorial belt.
3. The critical photoperiod was less than 13 h in five samples, all from the tropics, or southern hemisphere. The remaining samples, including three from the southern hemisphere, had critical photoperiods of 13 h or more.
4. Diapause was completely avoided by a 15 h photoperiod at 20°C in thirteen of the twenty-three samples, including all but one of those from the southern hemisphere.
5. At 25°C larvae entered diapause in short photoperiods (LD 9:15) in about half of the samples tested in both hemispheres, but the proportion per sample was always less than a third.     

Nonisothermal heat resistance determinations with the thermoresistometer Mastia

Aims:  To design and build a thermoresistometer, named Mastia, which could perform isothermal and nonisothermal experiments.
Methods and Results:  In order to evaluate the thermoresistometer, the heat resistance of Escherichia coli vegetative cells and Alicyclobacillus acidoterrestris spores was explored. Isothermal heat resistance of E. coli was characterized by D _60°C = 0·38 min and z =  4·7°C in pH 7 buffer. When the vegetative cells were exposed to nonisothermal conditions, their heat resistance was largely increased at slow heating and fast cooling rates. Isothermal heat resistance of A. acidoterrestris was characterized by D _95°C = 7·4 min and z =  9·5°C in orange juice. Under nonisothermal conditions, inactivation was reasonably well predicted from isothermal data.
Conclusions:  The thermoresistometer Mastia is a very suitable instrument to get heat resistance data of micro-organisms under isothermal and nonisothermal treatments.
Significance and Impact of the Study:  The thermoresistometer Mastia can be a helpful tool for food processors in order to estimate the level of safety of the treatments they apply.     

The survival of Salmonella enterica serovar Typhimurium DT104 and total viable counts on beef surfaces at different relative humidities and temperatures

Aims:  The aim of this study was to investigate changes in Salmonella and total viable count (TVC) survival on beef carcass surfaces stored for 72 h under different combinations of relative humidity (i.e. RH 75% or 96%) and temperature (5°C or 10°C).
Methods and Results:  The influence of low water activity ( a _w) and temperature on the survival and growth of Salmonella enterica serovar Typhimurium DT104 and the aerobic mesophilic flora on meat pieces from different sites on beef carcasses was investigated, under controlled conditions (75% or 96% RH; 5 or 10°C) in an environmental cabinet. Salmonella counts declined during storage at low a _w (75% RH) conditions at 5°C or 10°C. Salmonella counts increased during storage at high a _w (96% RH) at 10°C only. At 5°C, TVCs increased during storage at high a _w, but not at low a _w. TVCs increased on all samples from carcasses stored at high or low a _w at 10°C, except those samples taken from areas of surface fat.
Conclusions:  This suggests that substrate composition dictates growth rates under low a _w conditions. The results are discussed in terms of the possible protective effects of substrate osmolyte accumulation in bacterial survival and/or growth.
Significance and Impact of the Study:  The data obtained in this study provides useful insights on the influence of a _w and temperature on pathogen survival on meat surfaces at chill temperature.     

Egg development of the stoneflies Siphonoperla burmeisteri(Chloroperlidae) and Dinocras cepùnalotes(Perlidae)

SUMMARY. 1. The duration of egg incubation ( Y ) in Dinocras cephalotes and Siphonoperla burmeisteri was related to constant temperatures from 4 to 24°C, by the regression equations Y=2382 T ^{− 1, 402}(r²=0.992, P<0.001) and y= 2683 T ^−1.667 ( r ²=0.994, P <0.001), respectively. No diapause was observed in either species.
2. Egg incubation in D. cephaloles was slow and took 784.9±92.7 (mean ± SD) degree days between 12 and 20°C. significantly more than in S. burmeisteri (445±76.17 degree days: t = 7.44. d.f.=13, P <0.001).
3. For D. cephalotes hatching occurred at temperatures between 12 and 24°C, and for S . burmeisteri between 8 and 20°C. The mean volume of the eggs of D. cephalotes was about 5 times greater than that of S. burmeisteri and the mean body lengths of the newly-hatched nymphs were 1.13 mm and 0.95 mm respectively.
4. This study shows that the freshwater fauna of northern Fennoscan- dia also contains species with warm stenotherm eggs. D. cephalotes. which is of a Mediterranean origin (Zwick, 1981a), may exist at the limit of its distribution in northern Fennoscandia.     

Phytoplankton responses to experimental enhancement of grazing pressure and nutrient recycling in a small Andean lake

1. Three series of field experiments with different zooplankton species composition and biomass were performed in a small lake in the south Andes. We attempted to measure the responses of phytoplankton species resulting from grazing mortality and stimulation of growth by nutrient recycling.
2. Nanoflagellates contributed substantially to total phytoplankton cell abundance. Chrysochromulina parva represented 93.4%, 92.2% and 95.9% of total phytoplankton density in December, January and February, respectively. This fraction was reduced in all treatments with increasing zooplankton biomass.
3. A negative relationship was obtained between C. parva cell numbers and increase in dissolved P. On the other hand, a significant positive relationship between the abundance of the diatom Aulacoseira granulata and P concentration was observed. These results indicate that the ungrazed diatom was able to capitalise on the increase in nutrient availability.
4. As a net result of the increase or decrease of algal species we observed a change in the nano:net phytoplankton relationship. The outcome of three‐day incubations with increased zooplankton biomass was an increasing importance of net phytoplankton.
5. The results indicate the importance of the indirect effects of zooplankton (through nutrient recycling) in the increase in diatoms, and the role of grazing as a growth‐limiting factor for the flagellate C. parva .     

Temperature effects on bioconcentration of DDE by Daphnia

1. Lake temperatures vary with season, latitude, elevation and as a result of thermal pollution. In addition, lake temperatures may increase with global warming. Radiotracer experiments were conducted to determine the effects of temperature on the bioaccumulation of lipophilic organic contaminants by zooplankton. Daphnia pulex were exposed to ¹⁴C-labelled DDE, a stable metabolite of the organochlorine pesticide DDT, in particle-free water for 24 h. An increase in temperature from 5 to 25 °C resulted in a 314% increase in bioconcentration factor (the ratio of contaminant concentration in the organism to contaminant concentration in the water).
2. To mimic the fluctuating temperatures experienced by zooplankton during diel vertical migration, we conducted experiments in which animals were exposed to 25 °C for 12 h in the light, then 15 °C for 12 h in the dark. Exposure to this fluctuating temperature regime for 48 h resulted in a 27–33% increase in bioconcentration factor relative to a constant 20 °C control.
3. Live animals accumulated more than twice the amount of DDE than freshly killed animals, indicating that the activity of the organism is important in bioconcentration. This finding sheds light on the possible mechanisms for the increase in bioconcentration at higher constant temperatures. Daphnia pump more water through their branchial chambers at higher temperatures. Thus, if the thoracic limbs are an important site of contaminant uptake, then animals are exposed to more contaminant molecules at higher temperatures. Other possible mechanisms include changes in the thickness of the diffusive boundary layer and changes in cell membrane permeability.     

STIMULATION OF PIRIFORM- AND NEO-CORTICAL TISSUES IN AN IN VITRO FLOW-SYSTEM: METABOLIC PROPERTIES AND RELEASE OF PUTATIVE NEUROTRANSMITTERS

Abstract— (1) Multiple samples from the piriform cortex and neocortex of the guinea pig were maintained in separate incubation vessels through which incubation solutions based on Krebs-Ringer bicarbonate glucose media were caused to flow for chosen periods at specified rates.
(2) The tissues were held in defined positions in relation to electrodes; in some experiments electrical stimuli were applied and in others incubation media were changed with respect to their oxygen, K⁺ or glutamate content.
(3) With media flowing at 3–4 ml/min, the incubated tissues were similar in contents of K salts and phosphocreatine, and in rate of glycolysis to those incubated in non-flowing media. The tissues responded to electrical stimulation by increase in glycolysis and decrease in phosphocreatine and K content.
(4) During pre-incubation periods in non-flowing media, samples of piriform cortex were exposed to solutions containing ³H-labelled glycine, noradrenaline or 5-hydroxytry-ptamine and on anlaysis were found to contain the labelled compounds at concentrations four to seven times those of the surrounding media. The labelled compounds were gradually released into the flowing incubation media, and the release of noradrenaline and 5-hydroxytryptamine was accelerated by electrical stimulation.
(5) Release of the two bases was also modified by added reagents and the course of their release is discussed in relation to other metabolic changes concomitantly observed.     

Temperature effects on bioconcentration of DDE by Daphnia

1. Lake temperatures vary with season, latitude, elevation and as a result of thermal pollution. In addition, lake temperatures may increase with global warming. Radiotracer experiments were conducted to determine the effects of temperature on the bioaccumulation of lipophilic organic contaminants by zooplankton. Daphnia pulex were exposed to ¹⁴C-labelled DDE, a stable metabolite of the organochlorine pesticide DDT, in particle-free water for 24 h. An increase in temperature from 5 to 25 °C resulted in a 314% increase in bioconcentration factor (the ratio of contaminant concentration in the organism to contaminant concentration in the water).
2. To mimic the fluctuating temperatures experienced by zooplankton during diel vertical migration, we conducted experiments in which animals were exposed to 25 °C for 12 h in the light, then 15 °C for 12 h in the dark. Exposure to this fluctuating temperature regime for 48 h resulted in a 27–33% increase in bioconcentration factor relative to a constant 20 °C control.
3. Live animals accumulated more than twice the amount of DDE than freshly killed animals, indicating that the activity of the organism is important in bioconcentration. This finding sheds light on the possible mechanisms for the increase in bioconcentration at higher constant temperatures. Daphnia pump more water through their branchial chambers at higher temperatures. Thus, if the thoracic limbs are an important site of contaminant uptake, then animals are exposed to more contaminant molecules at higher temperatures. Other possible mechanisms include changes in the thickness of the diffusive boundary layer and changes in cell membrane permeability.     

Combining heat treatment and subsequent incubation temperature to prevent growth from spores of non-proteolytic Clostridium botulinum

Refrigerated processed foods of extended durability rely on a mild heat treatment combined with refrigerated storage to ensure microbiological safety and quality. The principal microbiological safety risk in foods of this type is non-proteolytic Clostridium botulinum. In this article the combined effect of mild heat treatment and refrigerated storage on the time to growth and probability of growth from spores of non-proteolytic Cl. botulinum is described. Spores of non-proteolytic Cl. botulinum (two strains each of type B, E and F) were heated at 90°C for between 0 and 60 min and subsequently incubated at 5°, 10° or 30°C in PYGS broth in the presence or absence of lysozyme. The number of spores that resulted in turbidity depended on the combination of heat treatment, incubation time and incubation temperature they received. Heating at 90°C for 1 or more min ensured a 10⁶ reduction when spores were subsequently incubated at 5°C for up to 23 weeks. Heating at 90°C for 60 min ensured a 10⁶ reduction over 23 weeks when subsequent incubation was at 10°C in the presence of added lysozyme. The same treatment did not reduce the spore population by 10⁶ when subsequent incubation was at 30°C.     

Thermal ecology of western tent caterpillars Malacosoma californicum pluviale and infection by nucleopolyhedrovirus

Abstract 1. Western tent caterpillars hatch in the early spring when temperatures are cool and variable. They compensate for sub-optimal air temperatures by basking in the sun.
2. Tent caterpillars have cyclic population dynamics and infection by nucleopolyhedrovirus (NPV) often occurs in populations at high density.
3. To determine whether climatic variation might influence viral infection, the environmental determinants of larval body temperature and the effects of temperature on growth and development rates and larval susceptibility to NPV were examined.
4. In the field, larval body temperature was determined by ambient temperature, irradiance, and larval stage. The relationship between larval body temperature and ambient temperature was curvilinear, a property consistent with, but not necessarily limited to, behaviourally thermoregulating organisms.
5. Larvae were reared at seven temperatures between 18 and 36 °C. Larval growth and development increased linearly with temperature to 30 °C, increased at a lower rate to 33 °C, then decreased to 36 °C. Pupal weights were highest for larvae reared between 27 and 30 °C.
6. The pathogenicity (LD₅₀) of NPV was not influenced by temperature, but the time to death of infected larvae declined asymptotically as temperature increased.
7. Taking into account larval growth, the theoretical yield of the virus increased significantly between 18 and 21 °C then decreased slightly as temperatures increased to 36 °C.
8. Control and infected larvae showed no difference in temperature preference on a thermal gradient. The modes of temperature preference were similar to those for optimal growth and asymptotic body temperatures measured in the field on sunny days.
9. Warmer temperatures attained by basking may increase the number of infection cycles in sunny springs but do not protect larvae from viral infection.