Field and laboratory studies on the timing of oviposition and hatching of the western black-legged tick, Ixodes pacificus (Acari: Ixodidae)

The timing of oviposition and hatching of Ixodes pacificus was investigated in the field and at constant temperatures in the laboratory. Replete females held at temperatures between 9 and 29°C began depositing eggs a mean of 9–70 days after drop off. Egg masses held between 12 and 25°C commenced hatching 25–178 days after the onset of oviposition. Eggs held at 9 or 29°C did not hatch. The lower temperature thresholds for development (LTD) for oviposition and hatching were 6.5 and 9°C, respectively. The number of degree days required for oviposition and hatching was 173 and 588, respectively. Replete females placed in the field on 2 December through to 8 March deposited eggs from 2 February through to 24 April; the eggs commenced hatching between 2 July and 21 August. Unfed larvae from two of 20 egg masses survived through the winter and fed readily when exposed to deer mice (Peromyscus maniculatus) on 22 April. Replete larvae were returned to the field and moulted between 9 and 21 August. Larvae exposed to deer mice in August, 4 weeks after hatching, also fed readily. Although further studies are needed to clarify the timing of nymphal development, the present study suggests that I. pacificus requires more than 1 year to complete its life cycle.     

The Effect of Acute Stress and Temperature on Plasma Cortisol and ion Concentrations and Growth of Lake Inari Arctic Charr, Salvelinus Alpinus

One year old, individually tagged Lake Inari Arctic charr, Salvelinus alpinus, were reared at three constant temperatures, 10.3°C, 14.1°C and 18.1°C, over four weeks. Blood samples were collected from a group of unstressed fish after the cultivation period at the same time as another group of fish were subjected to acute handling stress treatment (2min netting in air and 40min (± 20min) recovery period in water). Plasma cortisol, calcium, sodium, potassium and chloride concentrations were measured on both groups. To study the effect of minor daily temperature fluctuations on the stress response of Arctic charr, two additional daily fluctuating temperature (14 ± 1°C, 18 ± 1°C) treatments were established. The samples were taken in the same manner as those in the constant temperature treatments. Growth was fastest at 10.3–14.1°C and clearly lower at 18.1°C. Pre-stress plasma cortisol levels were low but increased slightly with increasing temperature. After stressor treatment, the cortisol concentrations of Arctic charr were clearly higher in all temperature treatments but there were no significant differences in plasma cortisol concentrations among temperatures. Plasma calcium levels increased during the stress treatment but temperature did not modulate this effect. The plasma potassium concentrations declined at 14.1–18.1°C after acute stress but the response was not affected by temperature within this range. The concentrations of sodium and chloride were unaffected by acute stress. Temperatures of 10.3–18.1°C and fluctuating temperature treatments had no influence on any plasma ion concentrations. Arctic charr were able to maintain the plasma ion concentrations in fresh water at 10.3–18.1°C and after acute stress treatment. Results indicate that the optimum temperature for growth of Arctic charr has little to do with the plasma ion concentrations or the ability to maintain those concentrations after short-term stress. The plasma cortisol responses further indicate that the optimum temperature for growth of Arctic charr is not related to the suppressed ability to react to an acute handling stressor. Temperature fluctuations did not cause significant differences in cortisol levels when compared with constant temperatures.     

Temperature-controlled under-water egg dormancy and postflood hatching in Isotoma viridis (Collembola) as forms of adaptation to annual long-term flooding

Summary Incubation experiments with eggs of a population of Isotoma viridis, which is exposed to annual long-term flooding from about April to July, as well as field observations show that temperature controls both, underwater egg dormancy and immediate postflood hatching. The population is located at the Eder Freshwater Reservoir in Germany.If constant experimental temperatures are above 14°C, almost all eggs are nondormant. Dormancy is established at temperatures below 15°C, but embryonic development is completed. Experiments indicate that of the environmental factors that change drastically at the end of submergence (light, turgor pressure, oxygen, a.o.), only temperature acts as a hatching trigger. Hatching of the previously dormant eggs occurs at a constant threshold temperature of 16°C, mainly within 2 to 20 days after temperature elevation, but most of these eggs need even higher temperatures to hatch. Remaining eggs were partly stimulated to hatch by recooling them at 7°C for some days and then rewarming them again.The threshold temperatures observed are unusually high for Collembola and seem to be the result of selection by the special floodplain conditions. During normal years, the surface temperatures of submerged soil usually do not exceed threshold limits before summer drainage. This allows both, protection from under-water hatching and an optimal timing of hatching at the very beginning of the main terrestrial period. The experiments show that above the threshold temperature (in warm summers), individuals can hatch under water and survive submerged for 10–15 days. They can survive even longer in the water habitat, if emergent structures enable them to climb onto the water surface. Furthermore, a considerable polymorphism observed in some hatching properties improves the chance to survive under the unpredictable floodplain conditions.     

Biology of the shore fly Scatella stagnalis in rockwool under greenhouse conditions

The development times and survival of immature stages in rockwool and the fecundity and longevity of adult Scatella stagnalis were determined and stage-specific life-tables constructed for the species at constant 20 and 25 °C and at a fluctuating temperature (23–34 °C, mean 28.5 °C). Development time from egg to adult decreased with temperature, being 15.9±0.1 days at 20 °C, 11.4±0.1 days at 25 °C and 10.1±0.2 days at fluctuating temperature with mean of 28.5 °C. The lower threshold for egg-to-adult development was 6.4±2.7 °C and the total quantity of thermal energy required to complete development was 212.8±.0 °C. The proportion of females in two populations studied was 0.521. High temperature increased the mortality of pupae from 7% (20 °C) and 10% (25 °C) to 29% at 28.5 °C. At 25 °C, female longevity was 15.5±0.7 days and fecundity 315±19 eggs/female (20.4 eggs/female/day). Males lived for 22.0±1.1 days. At constant 25 °C, the net reproductive rate was 126.1 female eggs/female, generation time was 18.4 days, the doubling time of the population 5.3 days, and the intrinsic rate of increase (r _m) 0.263 day^–1.     

Effects of ambient Lake Mohave temperatures on development,oxygen consumption,and hatching success of the razorback sucker

Synopsis Spawning of razorback suckers,Xyrauchen texanus, in Lake Mohave occurred from 10–22°C and larvae were collected at water temperatures from 10–15°C in 1982 and 1983. In the laboratory, hatching success was similar from 12–20°C, but reduced hatching success was found at 10°C while none hatched a 8°C. Development rate and oxygen consumption were positively related to incubation temperature. Direct effects of ambient Lake Mohave water temperatures on hatching success of razorback sucker embryos are considered minimal. Historical spawning temperatures for the species are hypothesized based upon successful incubation temperatures and comparison to the white sucker,Catostomus commersoni.     

Hatching of Brachionus Rubens O. F. Muller resting eggs (Rotifers)

After a dormant period at low temperature (5°C) and darkness, hatching of Brachionus rubens resting eggs is induced by an increase of temperature (10–22°C) in presence of light.     

Metal concentrations in surficial sediments from hypersaline lakes,Australia

A major drawback to the use in aquaculture of members of the Eubranchiopoda from temporary pool environments is that their eggs do not hatch readily. An investigation of the factors influencing the hatching of eggs of the fairy shrimpStreptocephalus macrourus, showed that light was the only factor of those investigated that was obligatory for hatching. It was found that eggs which had not been desiccated hatched successfully in the presence of absence of adults, while those which had been desiccated showed a block in hatching initially, although this block deteriorated with time and after approximately two months the eggs which had been desiccated showed a similar hatching success to that of the non-desiccated eggs. Exposure of eggs to extremes of heat or cold before incubation did not influence the hatching success of the eggs significantly, but the temperature at which incubation took place was important. The optimal range lay between 14 °C and 20 °C. Eggs hatched and nauplii survived at dissolved oxygen tensions of below 0.5 mg 1^–1     

Synchrony in the hatching of eggs in the desert locust <Emphasis Type="Italic">Schistocerca gregaria</Emphasis> (Orthoptera: Acrididae): egg condition influences hatching time in the laboratory and under simulated field temperatures

This study examined the time of hatching of the desert locust Schistocerca gregaria Forskål (Orthoptera: Acrididae) in the laboratory to test the effect of eggs within a pod versus individualized eggs. The pod organization of eggs is thought to play a role in controlling hatching time and to facilitate synchronous hatching at constant temperatures. In the present study, we examined the hatching times of eggs in a pod and individualized eggs under 24-h thermocycles and simulated field temperatures. We tested two patterns of thermocycles consisting of a 12-h thermoperiod (35 or 30 °C) and 12-h cryoperiod (low temperature period; 30 or 25 °C), and two patterns of field temperatures observed in a natural habitat, Mauritania, in May and September. The majority of eggs hatched during low temperature periods in all patterns tested. In addition, the variances of hatching times for individualized eggs were significantly greater than for egg pods in which a clear peak of time of hatching was observed. We show that egg condition influences hatching time under thermocycles of constant and fluctuating temperatures in the laboratory, and may play a role in the adaptive time of hatching.     

Early warning of egg hatching in pea moth (Cydia nigricana)

Female pea moths (Cydia nigricana) kept at 23 ^oC began to lay eggs 2–3 days after emergence, lived for 16–21 days and laid on average 71 eggs. Individuals kept in field cages lived for slightly longer and laid on average 91 eggs. About 85% of eggs were laid during the first 11 days of the oviposition period, usually in the late afternoon and early evening. The relationship between the rate of egg development and temperature was defined. The estimated developmental zero was 9-4 ^oC at constant temperatures and 8-5 ^oC at fluctuating temperatures. Above 28 ^oC mortality increased and above 31 ^oC development was apparently retarded. Development at constant temperatures took 6–16% longer than at fluctuating temperatures with the same mean. Estimates of hatching dates in the field made from temperature data recorded at several sites in and near a pea crop, and 8 km distant, were usually within a day of the observed date. In warm weather, estimated and observed dates usually coincided; in cooler weather hatching was 2–3 days later than expected. Hatching dates predicted from temperature data after only 80% of development had occurred were correct on 28 out of 36 occasions. An example is given to show how the method could be used eventually with a sex attractant trapping system to provide early warning of first hatching and spraying dates.     

Effect of temperature on the ovipositional biology and egg viability of the cattle tickBoophilus annulatus (Acari: Ixodidae)

The effect of temperature on the ovipositional biology ofBoophilus annulatus (Say) was determined under laboratory conditions. Engorged females subjected to constant temperatures of 12 and 45°C died without ovipositing, while females held at 15 and 40°C laid eggs which did not hatch. The preoviposition period at 25–40°C was 2–3 days; however, significant increases occurred at 20°C (5.2 days) and at 15°C (16.3 days). The number of eggs laid per female was ca. 2700 at temperatures of 25–35°C, but decreased significantly at 20°C (ca. 2300 eggs/female), 15°C (ca. 1800 eggs/female), and at 40°C (ca. 300 eggs/female). No differences were observed in the Conversion Efficiency Index (CEI) values at temperatures of 20–30°C (ca. 50%), while temperatures of 15 and 40°C produced the lowest CEI values at 35.6 and 4.9%, respectively. Hatch-ability of eggs was ca. 80% at temperatures of 20–35°C. Incubation period of eggs ranged from 52.2 days at 20°C to 16.2 days at 35°C. The thermal threshold for egg development determined by linear regression was 12.9°C. Females subjected to four fluctuating temperature regimes produced no differences in number of eggs/female (ca. 2400), CEI (ca. 50%), or hatchability of eggs (ca. 75%). Preoviposition period and incubation were significantly affected by a change in the thermoperiod, becoming longer in duration as the temperatures were decreased. From studying females exposed for various intervals from 0 to 105 days at 12°C, indications were that the longer the exposure period the more adverse the effects were on oviposition and egg-hatch. Correspondingly, exposure of eggs to a temperature of 15°C for up to 105 days gave indications that the longer the eggs remained at 15°C, the lower the hatch would be after transfer back to a temperature of 25°C.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

Comparison of the hatching process of the tadpole shrimps Triops cancriformis and Lepidurus apus lubbocki (Notostraca) and its relation to their distribution in rain-pools in Israel

Rain-pool habitats are gradually disappearing in Israel as a result of agricultural and urban development. Present and past records of notostracan distribution here reveal a difference in the occurrence of Triops cancriformis and Lepidurus apus lubbocki, the former rather rare, and support the suggestion that species of Triops are more thermophilic than Lepidurus, with optimal hatching temperature 8–12°C higher. The limited distribution of T. cancriformis in Israel may be partly attributed to sub-optimal temperatures (<20°C) in early winter.All populations of T. cancriformis in Israel were monosexual female. Resting Notostraca eggs float and become exposed to light, needed for hatching, and to warm day-time temperatures at the water surface which enhance embryonic development. Exposure to higher temperatures may be particularly important for the thermophilic T. cancriformis in Israel, where deep water temperatures in early winter are often below hatching values.     

Effect of four fluctuating temperature regimes on cui-ui,Chasmistes cujus,survival from egg fertilization to swim-up,and size of larvae produced

Synopsis We evaluated cui-ui,Chasmistes cujus, swim-up success, time of hatching and swim-up, and size of larvae at swim-up under four fluctuating temperature regimes (8.9–15.0, 12.2–18.3, 15.0–21.1, and 17.8–23.9° C). The greatest swim-up success was at the 8.9–15.0° C regime and the lowest at the 15.0–21.1° C regime. Hatching and swim-up time varied inversely with incubation temperature. The largest (and presumably the most fit) larvae were in the 8.9–15.0° C treatment, whereas the smallest were in the 17.8–23.9° C treatment. Cui-ui appeared best adapted to the coolest of the four temperature regimes.     

Effects of temperature and humidity on the development and hatching of eggs of the thistle lacebug, Tingis ampliata (Heteroptera, Tingidae)

At constant temperatures in the laboratory, the rate of development (i.e. the reciprocal of the time of development in days) of eggs of T. ampliata increased with temperature in the range 15–30°C and threshold temperature for egg development was calculated to be 8.2°. The percentage of eggs hatching tended to increase with temperature, but hatching at 25° was not significantly different from that at 30° and no eggs hatched at 10°. A formula for predicting egg-developmental time at known temperature is provided.At 25° incubation period decreased and the percentage of eggs hatching increased with increase in relative humidity from 51–53% to 100 per cent. Embryonic development and egg hatching were inhibited at relative humidities below 51–53 per cent.

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Résumé La vitesse du dévelopment (c'est-à-dire la réciproque de la durée du développement en jours) des ufs de Tingis ampliata soumis au laboratoire à des conditions constantes de température, s'accroît avec cette température pour une gamme comprise entre 15 et 30°, cependant que la température limite inférieure pour le développement est de 8°2. Le pourcentage d'ufs écols tend à augmenter avec la température mais l'éclosion à 25° n'est pas significativement différente de celle à 30° et aucun uf n'éclot à 10°. Une formule est proposée permettant de prédire la durée de développement des ufs à une température donnée.Pour une température de 25°, la durée d'incubation et le pourcentage d'éclosion des ufs s'accroissent avec l'humidité relative (de 51–53% à 100%). Le développement embryonnaire et l'éclosion sont inhibés par une humidité relative inférieure à 51–53%.

     

Influence of temperature on hatching of eggs of Lepidurus couesii (Crustacea,Notostraca)

Tadpole shrimps (Notostraca) occur sporadically in temporary ponds and their survival there depends largely upon the drought-resistant eggs they produce. Environmental conditions conducive to hatching of eggs of Lepidurus couesii were investigated in the laboratory. Almost all eggs hatched best at 20 °C, whether desiccated for a short or long period, with a prior freezing shock or without such a shock, with intact shells. Eggs that endured a longer period of desiccation and eggs with abraded shells displayed a more equivocal response to different temperatures for hatching. Long-term hatchability of eggs was demonstrated. Time required for successful hatching was shortest at 20 °C, with no discernible difference between 17 °C and 25 °C. Both short- and long-term survival of populations of the species appears to be fostered by the adaptive response to temperature shown by the eggs.     

Laboratory studies of factors affecting egg hatch of triops longicaudatus (LeConte) (Notostraca : Triopsidae)

Egg hatch was greatest (78.33%) for eggs not previously desiccated. A reduction in numbers hatched occurred as the relative humidity at which they were dried decreased. Some eggs hatched (0.67–79.33%) at pH levels of 3.10–10.01 with the highest hatch at pH 5.60. Water temperature greatly affected egg hatch. No hatch occurred until temperatures were above 14°C. A constant 29°C significantly inhibited hatching. Egg hatch increased 13.00 to 43.42% as salinity decreased from 2200 to 9.24 micromhos/cm. As little as 13 mm of flooded soil covering the eggs prevented them from hatching for 14 days. Eighteen percent hatch resulted when soil and eggs were redistributed to a 1 mm soil layer. Egg samples from the same parent, even though treated similarly, often hatched at greatly varying rates and only rarely was hatching 100% within a replication.     

Survival of Coregonus albula (L.) (Teleostei) embryos incubated at different thermal conditions

Eggs of Coregonus albula were incubated at constant temperatures: 1.1, 2.0, 2.9, 4.9, 6.6, 8.4, and 9.9 °C, and the percentage of normal hatch was 20.6, 11.8, 30.4, 61.0, 51.7, 32.6, and 14.6%, respectively. The lower and upper median tolerance limit (TL 50) defined as the interpolated temperature at which embryos survival to hatch was 50% of the highest response (61% at 4.9 °C) were 2.9 and 8.5 °C, respectively. The optimum temperature range delimited by lower and upper TL 75 was encompassed by 4.0 and 7.2 °C.Eggs of C. albula incubated at variable temperature in a commercial hatchery showed a very high survival (up to 76%). Similarly low survival observed during hatching of embryos at constant temperatures of 1.1 and 2.0 °C could be hightened (to about 90%) by raising the temperature in the beginning of hatching period. This phenomenon was utilized in the technique of delaying C. albula embryos' mass hatching for the purpose of synchronization in time of stocking the lakes with the time of appearence of good thermal and food conditions for C. albula larvae.The conception of the optimal thermal conditions for Coregoninae embryogenesis was developed as the course of incubation temperature, securing the highest survival rate during embryogenesis and also during the larval period.     

Growth, survival, and starvation resistance of Colorado squawfish larvae

Synopsis Growth and survival of Colorado squawfish, Ptychocheilus lucius, larvae under fluctuating 18, 22, and 26° C (5° C diel fluctuations) and constant 18, 22, 26° C, and 30° C temperature conditions and ration size corresponding to 12.5, 28,64,142, 320 brine shrimp nauplii fish^–1 day^–1 determined from laboratory experiments. Growth was optimal at 31° C and high at temperatures of 26° C to 30° C, at the highest food abundance. Lowest growth was under lowest food rations and highest temperatures. Growth of Colorado squawfish larvae declined substantially at temperatures < 22° C. Neither growth nor survival was significantly different between fluctuating or constant regimes. Survival of Colorado squawfish larvae was highest (95%) at 26.2° C and 235 nauplii fish^–1 day^–1 and high at temperatures of 20 to 30° C with food abundance > 180 nauplii fish^–1 day^–1. Survival was lowest when food abundance was low and temperature was high. Highest mortality occurred more than 20 days after experiments began and mortalities occurred sooner in higher than lower temperatures. Colorado squawfish larvae denied food for 5, 10, or 15 d after first feeding could have begun (6 d), had survival greater than 87 % which was equivalent to continuously fed controls. Survival of fish denied food for 17.5 d after feeding could have begun declined from 84% before feeding to 57% after feeding. Point of no return was estimated between 17.5 and 20 d. Colorado squawfish have relatively high starvation resistance. Low, stable flows that simulate natural hydrographs may enhance growth, survival, and recruitment of early life stages of Colorado squawfish by increasing water temperature and food abundance in regulated rivers of the Colorado River basin.     

恒定和波动温度下丽斑麻蜥孵出幼体的表型变异

作者以丽斑麻蜥(Eremias argus)为模型动物研究恒定和波动孵化温度对孵化成功率和孵出幼体表型的影响。卵在四个恒定[24 ,27 ,30 and 33 (±0·3)℃]、一个波动温度下孵化。不同温度处理下的孵化成功率相同,但孵出幼体表型不同。孵化期随孵化温度升高呈指数式缩短;在相同平均温度下,波动温度孵化卵的孵化期比恒温孵化卵长。在所有被检表型特征中,幼体的干重、剩余卵黄干重和运动表现更易受孵化温度影响。总体而言,低温(24℃、27℃)孵出幼体运动表现最佳,高温(33℃)孵出幼体最差、温和温度(30℃和波动温度)孵出幼体居中。本文研究数据显示: (1)丽斑麻蜥卵每日短期暴露于潜在致死的极端温度下对孵化成功率和孵出幼体形态特征无明显的不利效应; (2)温度波动对孵出幼体运动表现无促进作用,对孵化期的影响则不同于平均值相同的恒定温度。     

Life-table study of Anagrus atomus, an egg parasitoid of the green leafhopper Empoasca decipiens, at four different temperatures

The objective of our study was to assess thepotential of the egg parasitoid Anagrusatomus L. (Hymenoptera: Mymaridae) for controlof the greenhouse leafhopper Empoascadecipiens Paoli (Homoptera: Cicadellidae). Theegg-adult development time, survivorship andreproduction of A. atomus were evaluatedat four constant temperatures (16, 20, 24 and28°C). Developmental time ranged from33.6 days at 16°C to 13.3 days at 28°C. Based on a linear regression ofdevelopment rate on temperature the lowerthreshold was estimated at 8.39°C. Anagrus atomus required 263.2 degree-days tocomplete its development from egg to adult. Theegg-adult survival rate and the sex ratio weresignificantly lower at 28°C than at theother three temperatures tested. The intrinsicrate of increase (r _m) variedsignificantly between all four temperatures.The potential of A. atomus to attackdifferent host ages was additionallyinvestigated. Host eggs were parasitizedthroughout their development but rate ofparasitism was reduced in host eggs older thansix days. The number of eggs parasitized waspositively density dependent but the rate ofparasitism decreased with increasing hostdensity. A maximum rate of parasitism of 62.5%was recorded. The potential impact of the eggparasitoid on the population dynamics of E. decipiens is discussed.