Emergence of Chironomidae from the shallow eutrophic Lake Kasumigaura,Japan

Seasonal chironomid emergence was monitored in the shallow eutrophic Lake Kasumigaura and 18 species were collected with a battery-operated light trap fixed on a floating stage and with surface emergence traps. During October–December, samples in the light trap comprised exclusively Tokunagayusurika akamusi (Tokunaga) and small numbers of one or two other species. T. akamusi, Procladuis (Holotanypus) culiciformis (L.), and Chironomus plumosus (L.) constituted 91.6% of the annual catch of chironomid adults. The predominance of T. akamusi (75.3 % of chironomid catch) and the high ratio (13) of T. akamusi to C. plumosus was more marked in this lake than other Japanese eutrophic lakes. Glyptotendipes tokunagai Sasa and Dicrotendipes pelochloris (Kieffer) were also caught abundantly with the light trap, but not with surface traps, indicating these were littoral species. The dry weight of emerging adults during May–December 1982 was 2.87 g m^–2, of which 1.92 gm^–2 (67%) was T. akamusi and 0.67 gm^–2 (23%) C. plumosus and 0.23 g m^–2 (8%) Clinotanypus sugiyamai Tokunaga and 0.03 gm^–2 (1%) P. (H.) culiciformis. The weight of emerging Tanypodinae was much higher than the annual mean larval biomass or estimated larval production, which have been due to underestimating the population density using an Ekman-Birge dredge. High numbers of individuals and species of chironomids were caught during April–July, presumably as a result of the high food supply for chironomid communities.     

Ammonia-nitrogen excretion in Daphnia pulex

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal^–1 day^–1 or 5.11 µg N mg^–1 dry body weight day^–1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log₁₀E = (0.061) T 1.773, where E is µg N animal^–1 day^–1 and T is temperature °C. The ammonia-nitrogen excretion on a mg^–1 dry body weight day^–1 basis was related to temperature according to the following similar expression Log₁₀E = (0.043) T + 0.153, where E is µg N mg^–1 dry body weight day^–1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log₁₀W = (0.526) Log₁₀L + 1.357, where W is weight in µg and L is length in mm.     

Purification and characterization of a high molecular mass serine carboxypeptidase from <Emphasis Type="Italic">Monascus pilosus</Emphasis>

Two serine carboxypeptidases, MpiCP-1 and MpiCP-2, were purified to homogeneity from Monascus pilosus IFO 4480. MpiCP-1 is a homodimer with a native molecular mass of 125 kDa composed of two identical subunits of 61 kDa, while MpiCP-2 is a high mass homooligomer with a native molecular mass of 2,263 kDa composed of about 38 identical subunits of 59 kDa. This is unique among carboxypeptidases and distinguishes MpiCP-2 as the largest known carboxypeptidase. The two purified enzymes were both acidic glycoproteins. MpiCP-1 has an isoelectric point of 3.7 and a carbohydrate content of 11%, while for MpiCP-2 these values were 4.0 and 33%, respectively. The optimum pH and temperature were around 4.0 and 50°C for MpiCP-1, and 3.5 and 50°C for MpiCP-2. MpiCP-1 was stable over a broad range of pH between 2.0 and 8.0 at 37°C for 1 h, and up to 55°C for 15 min at pH 6.0, but MpiCP-2 was stable in a narrow range of pH between 5.5 and 6.5, and up to 50°C for 15 min at pH 6.0. Phenylmethylsulfonylfluoride strongly inhibited MpiCP-1 and completely inhibited MpiCP-2, suggesting that they are both serine carboxypeptidases. Of the substrates tested, benzyloxycarbonyl-l-tyrosyl-l-glutamic acid (Z-Tyr-Glu) was the best for both enzymes. The K_m, V_max, K_cat and K_cat/K_m values of MpiCP-1 for Z-Tyr-Glu at pH 4.0 and 37°C were 1.33 mM, 1.49 mM min^–1, 723 s^–1 and 545 mM^–1 s^–1, and those of MpiCP-2 at pH 3.5 and 37°C were 1.55 mM, 1.54 mM min^–1, 2,039 s^–1 and 1,318 mM^–1 s^–1, respectively.     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Potential for aquatic oligochaetes as live food in commercial aquaculture

Aquatic oligochaetes may potentially become an important constituent in commercial aquaculture as a live food source. Tubifex tubifex, Limnodrilus species, Branchiura sowerbyi and the lumbriculid Lumbriculus variegatus have been economically mass cultured with production rates of 15 kg m^- and population doubling times of 11–42 days reported. Relatively high growth and survival rates of trout, salmon and sturgeon have been achieved in association with the use of this live food source. Benefits stem from advantages with increased appetites and palatability. As well, sanitation and heating requirements in fish hatchery situations may be reduced. Disease transmission must be prevented.     

Metabolic and cardiovascular adaptations in the western chipmunks, genusEutamias

Summary The metabolic and cardiac responses to temperature were studied in two species (four subspecies) of western chipmunks (genusEutamias), inhabiting boreal and alpine environments. A specially designed (Fig. 1) implantable biopential radiotransmitter was used to measure heart rate in unrestrained animals. The estimated basal metabolic rates (EBMR) were 1.78 (E. minimus borealis), 1.64 (E. m. oreocetes), 1.50 (E. m. operarius), and 1.69 ml O₂ g^–1 h^–1 (E. amoenus luteiventris), or 839, 752, 698, and 628 ml O₂ kg^–0.75 h^–1, respectively, for the four subspecies (Table 1). The two alpine species (E.m.or. andE.m.op.) had significantly lower EBMR than both of their boreal counterparts. The EBMR from all animals are 120–135% of the predicted values based on body weights of the animals. The thermal neutral zone for the four subspecies ranged from 23.5 to 32°C and the minimum thermal conductances were 0.113, 0.111, 0.112 and 0.112 ml O₂ g^–1 h^–1 °C^–1, respectively, or 54.4, 54.0, 50.4 and 52.1 ml O₂ kg^–0.75 h^–1 °C^–1, respectively (Fig. 2). No interspecific diffence in conductance was observed. These values are 72 to 85% of their weight specific values. The body temperature ranged between 35.0 and 39.5°C and was usually maintained between 36 and 38°C in all subspecies between ambient temperatures of 3 and 32°C. The estimated basal heart rates were 273, 296, 273 and 264 beats/min, respectively, for the four subspecies, 49–55% of their predicted weight specific values. The resultant oxygen pulses (metabolic rate/heart rate) were 5.49, 4.50, 4.48 and 5.56×10^–3 ml O₂/beat, respectively, which are 2 to 2.4 times their weight specific values (Table 2).The observed reduction of basal heart rate without the corresponding decreases of basal metabolic rate and body temperature indicate sufficient compensatory increases in stroke volume and/or A-V oxygen difference at rest. Such cardiovascular modifications provide extra reserves when demand for aerobic metabolism rises during bursts of activity typically observed in the western chipmunk.Abbreviations A-V arterio-venous - EBMR estimated basal metabolic rate (ml O₂ g^–1 h^–1) - HR heart rate (beats/min) - MR metabolic rate (ml O₂ g^–1 h^–1) - OP oxygen pulse (ml O₂/heart beat) - T_a, T_b ambient and body temperature (°C)     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Aerobic biodegradation of nonylphenol by cold-adapted bacteria

Three strains capable of mineralizing nonylphenol as sole carbon source were isolated from a sample of contaminated soil and characterized as two Pseudomonas spp. and a Stenotrophomonas sp. The two Pseudomonas spp. expressed characteristics typical of psychrophiles growing optimally of 10 °C and capable of growing at 0 °C. The Stenotrophomonas sp. was more likely psychrotrophic because it had an optimal temperature between 14 and 22 °C although it was not capable of growing at 4 °C. At 14 °C, one of the Pseudomonas spp. exhibited the highest rate of degradation of nonylphenol (4.4 mg l^–1 d^–1), when compared with axenic or mixed cultures of the isolates. This study represents, to the best of our knowledge, the first reported case of cold-adapted microorganisms capable of mineralizing nonylphenol.     

Nitrogen cycling in lake sediments bioturbated by Chironomus plumosus larvae, under different degrees of oxygenation

Sediment cores containing different densities of Chironomus plumosus, ranging from 0 to 12 000 ind. m^–2, were incubated in the laboratory, with 100 and 39% O₂ saturation in the overlying water. Rates of O₂ uptake, and fluxes of the various inorganic N species were measured after addition of ¹⁵NO _inf3 ^su– to the overlying water. The animals enhanced O₂ and NO _inf3 ^su– uptake, due to irrigation. Denitrification of NO _inf3 ^su– coming from the overlying water (Dw) and dissimilatory NO _inf3 ^su– reduction to NH _inf4 ^sup+ (DNRA) represented 20–30 and 4–10% of the NO _inf3 ^su– uptake, respectively. Only 20–40% of the measured NH _inf4 ^sup+ effluxes corresponded to DNRA, the rest was probably due to animal excretion. Nitrite production, mostly from dissimilatory NO _inf3 ^sup– reduction, was detected at both 39 and 100% oxygen saturation. Higher rates of NO _inf2 ^su– production at the lower oxygen concentrations, were probably due to a thinner oxic layer, compared to fully oxygenated waters. The presence of Chironomus plumosus increased nitrification rates, relative to non-inhabited microcosms. However, nitrification rates were low compared to Dw, probably due to low numbers of nitrifiers in the sediment. At 39% oxygen saturation, rates of nitrification and denitrification of NO _inf3 ^su– generated within the sediment were not measurable.     

Zooplankton as a compound mineralising and synthesizing system: phosphorus excretion

Data on phosphate excretion rates of zooplankton are based on measurements using the pelagic crustacean zooplankton of Lake Vechten and laboratory-cultured Daphnia galeata. In case of Daphnia sp we measured the effects of feeding on P-rich algae and P-poor algae (Scenedesmus) as food on the P-excretion rates at 20°C. The excretion rates of the natural zooplankton community, irrespective of the influence of the factors mentioned, varied by an order of magnitude: 0.025–0.275µg PO₄-Pmg^–1C in zooplankton (C _zp ) h^–1. The temperature accounted for about half the observed variation in excretion rates. The mean excretion rates in the lake, computed for 20°C, varied between 0.141 and 0.260 µg Pmg^–1C _zp h^–1. Based on data of zooplankton biomass in the lake the P-regeneration rates by zooplankton covered between 22 and 239% of the P-demand of phytoplankton during the different months of the study period.In D. galeata, whereas the C/P ratios of the Scenedesmus used as food differed by a factor 5 in the experiments, the excretion rates differed by factor 3 only. Despite the higher P-excretion rates (0.258± 0.022 µg PO₄-P mg^–1 C h^–1) of the daphnids fed with P-rich food than those fed with P-poor food (0.105 ± 0.047 µg PO₄-P mg^–1 C h^p–1), both the categories of the animals were apparently conserving P. A survey of the literature on zooplankton excretion shows that in Daphnia the excretion rates vary by a factor 30, irrespective of the species and size of animals and method of estimation and temperature used.About two-thirds of this variation can be explained by size and temperature. A major problem of comparability of studies on P-regeneration by zooplankton relates to the existing techniques of P determination, which necessitates concentrating the animals several times above the in situ concentration (crowding) and prolonged experimental duration (starving), both of which manifest in marked changes that probably lead to underestimation of the real rates.     

Purification and characterization of a new type of serine carboxypeptidase from<Emphasis Type="Italic"> Monascus purpureus</Emphasis>

Carboxypeptidase produced by Monascus purpureus IFO 4478 was purified to homogeneity. The purified enzyme is a heterodimer with a molecular mass of 132 kDa and consists of two subunits of 64 and 67 kDa. It is an acidic glycoprotein with an isoelectric point of 3.67 and 17.0% carbohydrate content. The optimum pH and temperature were 4.0 and 40 °C, respectively. The enzyme was stable between pH 2.0 and 8.0 at 37 °C for 1 h, and up to 50 °C at pH 5.0 for 15 min. The enzyme was strongly inhibited by piperastatin A, diisopropylfluoride phosphate (DFP), phenylmethylsulfonylfluoride (PMSF), and chymostatin, suggesting that it is a chymotrypsin-like serine carboxypeptidase. Monascus purpureus carboxypeptidase was also strongly inhibited by p-chloromercuribenzoic acid (PCMB) but not by ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline, indicating that it requires cysteine residue but not metal ions for activity. Benzyloxycarbonyl-l-tyrosyl-l-glutamic acid (Z-Tyr-Glu), among the substrates tested, was the best substrate of the enzyme. The K_m, V_max, K_cat, and K_cat/K_m values of the enzyme for Z-Tyr-Glu at pH 4.0 and 37 °C were 0.86 mM, 0.917 mM min^–1, 291 s^–1, and 339 mM^–1 s^–1, respectively.     

A laboratory study of phosphorus and nitrogen excretion of Euchlanis dilatata lucksiana

Phosphorus (PO₄-P) and nitrogen (NH₄-N) excretion rates of Euchlanis dilatata lucksiana, a rotifer, isolated from Lake Loosdrecht (The Netherlands) and cultured in the lake water at 18–19 °C, were measured in the laboratory.In a series of experiments, the effects of experiment duration on the P and N excretion rates were examined. The rates measured in the first half-hour were about 2 times higher for P and 2–4 times for N than the rates in the subsequent three successive hours which were quite comparable.Eight experiments were carried out in triplicate, 4 each for P and N excretion measurements, using animals of two size ranges: 60–125 µm and > 125 µm. The specific excretion rates varied from 0.06 to 0.18 µg P.mg^–1 DW.h^–1 and 0.21 to 0.76 µg N.mg^–1 DW.h^–1. Generally an inverse relationship was observed between the specific excretion rates and the mean individual weight. The excretion rates of Euchlanis measured by us are lower than those reported for several other rotifer species, most of which are much smaller than Euchlanis.Extrapolating the excretion rates of Euchlanis to the other rotifer species in Lake Loosdrecht, and accounting for their density, size and temperature, rotifer excretion appears to be a significant, potential nutrient (N,P) source for phytoplankton growth in the lake. The excretion rates for the rotifers appear to be about two thirds of the total zooplankton excretion, even though the computed rotifer mean biomass is about one-third of the total zooplankton biomass.     

Effects of artificial destratification on zoobenthos and on the trophic status of a Polish reservoir

The macro-benthic fauna, especially the Chironomidae, and the sequence of faunal groups in a horizontal transect across Lake Mutek (1977–79) before and after artificial destratification are described. Before destratification (1977–78), Chaoborus flavicans was the dominant species. After destratification this form decreased in numbers rapidly. Chironomidae and Oligochaeta first appeared in the open water zone. A multiple increase in density of pelophilous forms (Chironomus plumosus and C. thummi) was also observed. The trophic status of the lake shifted from polytrophic to eutrophic.     

Effect of torpor on the water economy of an arid-zone marsupial,the stripe-faced dunnart (<Emphasis Type="Italic">Sminthopsis macroura</Emphasis>)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T_a) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 (T_a=30°C) to 3.13±0.22 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor at T_a=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing T_a, and ranged from 1.81±0.37 (T_a=30°C) to 5.26±0.86 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H₂O h^–1. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T_a investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.     

Swimming Performances of Four California Stream Fishes: Temperature Effects

The critical swimming velocity (U_crit) of four California stream fishes, hardhead, Mylopharodon conocephalus, hitch, Lavinia exilicauda, Sacramento pikeminnow, Ptychocheilus grandis, and Sacramento sucker, Catostomus occidentalis was measured at 10, 15, and 20°C. Hardhead, Sacramento sucker, and Sacramento pikeminnow swimming performances tended to be lowest at 10°C, higher at 15°C, and then decreased or remained constant at 20°C. Hitch swimming performance was lower at 10°C than at 20°C. There were no significant differences among species at 10 or 15°C, although pikeminnow and hitch were ca. 20% slower than hardhead or sucker. At 20°C hardhead, Sacramento sucker, and Sacramento pikeminnow had remarkably similar U_crit but hitch were significantly (by 11%) faster. We recommend that water diversion approach velocities should not exceed 0.3ms^–1 for hitch (20–30cm total length) and 0.4ms^–1 for hardhead, Sacramento pikeminnow, and Sacramento sucker (20–30cm TL).     

Polyphenolic Antioxidants Efficiently Protect Urease from Inactivation by Ultrasonic Cavitation

Inactivation of urease (25 nM) in aqueous solutions (pH 5.0–6.0) treated with low-frequency ultrasound (LFUS; 27 kHz, 60 W/cm², 36–56°C) or high-frequency ultrasound (HFUS; 2.64 MHz, 1 W/cm², 36 or 56°C) has been characterized quantitatively, using first-order rate constants: k _in, total inactivation; k _in ^*, thermal inactivation; and k _in(us), ultrasonic inactivation. Within the range from 1 nM to 10 M, propyl gallate (PG) decreases by approximately threefold the rate of LFUS-induced inactivation of urease (56°C), whereas resorcinol poly-2-disulfide stops this process at 1 nM or higher concentrations. PG completely inhibits HFUS-induced inactivation of urease at 1 nM (36°C) or 10 nM (56°C). At 0.2–1.0 M, human serum albumin (HSA) increases the resistance of urease treated with HFUS to temperature- and cavitation-induced inactivation. Complexes of gallic acid polydisulfide (GAPDS) with HSA (GAPDS–HSA), formed by conjugation of 1.0 nM GAPDS with 0.33 nM HSA, prevent HFUS-induced urease inactivation (56°C).     

The combined relationship of temperature and molybdenum concentration to nitrogen fixation byAnabaena cylindrica

The joint effects of growth temperature, incubation temperature, and molybdenum concentration on the nitrogen fixation rate ofAnabaena cylindrica were determined using the acetylene-reduction technique. The nitrogen-fixation response to increased molybdenum concentration varied among three growth temperatures (15°, 23°, and 30° C). The pattern of rate change was similar within a growth temperature but increased overall in magnitude with the three incubation temperatures (also 15°, 23°, and 30° C). The maximum rate of nitrogen fixation occurred at 30°C regardless of previous growth temperature. The minimum molybdenum concentration necessary to yield substantial acetylene reduction varied with growth temperature: at 15°C, 15g 1^–1 was effective; at 23°C, less than 5g 1^–1 was effective; and at 30°C, 50g 1^–1 was effective. At all three growth temperatures, increases in molybdenum concentration above the minimum effective concentration produced increases in acetylene reduction. However, at higher molybdenum concentrations inhibition of nitrogen fixation occurred.     

Metabolism measurements ofAurelia aurita planulae larvae,and calculation of maximal survival period of the free swimming stage

Respiration, ammonia and phosphate excretion experiments were performed with planula larvae ofAurelia aurita (Scyphozoa) from Kiel Fjord, Baltic Sea, in summer 1983. The mean respiration measured was 3.22 nl O₂ ind^–1 h^–1 (at 20 °C). Excretion experiments revealed average values of 11.41 pM NH₄-N ind^–1, and 0.92 pM PO₄-P ind^–1h^–1, respectively. The atomic C:N:P ratio of excretion products was 133:10:1. The O:N ratio of 25:1 and O:P ratio of 313:1 point to a lipid-carbohydrate-oriented catabolism of theAurelia larvae. On the basis of experimental results and of biomass determinations, the maximal survival period of the non-feeding free swimming planula stage was calculated. Typically, the value lies in the range of some days to one week.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

The production of cyclopiazonic acid by Penicillium commune and cyclopiazonic acid and aflatoxins by Aspergillus flavus as affected by water activity and temperature on maize grains

The combined effects of water activity (a_w) and temperature on mycotoxin production by Penicilium commune (cyclopiazonic acid — CPA) and Aspergillus flavus (CPA and aflatoxins — AF) were studied on maize over a 14-day period using a statistical experimental design. Analysis of variance showed a highly significant interaction (P 0.001) between these factors and mycotoxin production. The minimum a_w/temperature for CPA production (2264 ng g^–1 P. commune, 709 ng g^–1 A. flavus) was 0.90 a_w/30 °C while greatest production (7678 ng g^–1 P. commune, 1876 ng g^–1 A. flavus) was produced at 0.98 a_w/20 °C. Least AF (411 ng g^–1) was produced at 0.90 a_w/20 °C and most (3096 ng g^–1) at 0.98 a_w/30 °C.