Delayed Egg Hatching and Semivoltinism in the Nearctic Stonefly Megarcys signata (Plecoptera: Perlodidae)

Delayed egg hatching can influence the survival of aquatic insects by reducing exposure to competitors, predators, parasites, or unfavorable environmental conditions. We examined egg development in a Colorado population of the stonefly, Megarcys signata (Plecoptera: Perlodidae), whose larvae inhabit high altitude streams in the Rocky Mountains of western North America. Five-thousand fertilized eggs were collected from 40 different females and incubated in the East River, Gunnison County, Colorado, until late fall, at which time unhatched eggs were transported to incubation chambers in Ithaca, New York. We used three different combinations of photoperiod and temperature (10L:14D, 4°C; 10L:14D, 8°C; 8L:16D, 8°C) in an attempt to induce hatching. Eggs in the treatments with temperatures elevated above normal winter temperatures in the East River (8°C) began developing after 6 months, whereas eggs in the treatment most closely simulating natural stream conditions (4°C) did not hatch after 10 months of incubation. Our data indicate that this population of Megarcys signata has an extended egg stage that persists for almost a year, and that it is semivoltine at these elevations of 2885 and 2895 meters.     

Effect of temperature on the morphometric development of eggs in the prawn Macrobrachium americanum (Caridea: Palaemonidae) and larval success under experimental conditions

Abstract

This study evaluated the effect of temperature on morphometric features of the egg during the embryonic development of the prawn Macrobrachium americanum and the relationship with hatching and the survival of the larvae. Berried females were grouped (n = 3) and reared at three different temperatures, 26, 29, and 33 °C, for which seven developmental stages were recognized. At each stage, the apical and sagittal diameters of the eggs were measured, the volume was calculated, and the weights were recorded. Additionally, the duration of embryonic development, hatching percentage, and larval survival were determined. At 29 and 33 °C, the eggs’ volume increased by 50%, but at 26 °C, the increase was 25%. Larvae from eggs incubated at 33 °C died one day after hatching. At 29 °C, larvae survived until Zoea VII. Larvae from eggs incubated at 26 °C died at the end of Zoea I. The number of days of embryonic development was 20.5 ± 1.5 (26 °C), 15 ± 1 (29 °C), and 12 ± 1 (33 °C). A temperature of 29 °C was the most favorable for embryonic development in M. americanum.     

Thermal effects on the biological parameters of the predatory mirid Pilophorus gallicus (Hemiptera: Miridae)

Pilophorus gallicus Remane (Hemiptera: Miridae) is a predatory mirid reported in deciduous trees in the western Mediterranean area. This work aimed to determine the biological and demographic parameters for this species at different temperatures (15, 20, 25 and 30°C). Egg hatching times shortened from 57.8 days at 15°C to 9.2 days at 30°C, and nymphal development times declined from 62.8 days at 15°C to 11.1 days at 30°C. The hatching and nymphal survival rates were low at 15 and 30°C. The lower thermal thresholds for the egg and nymphal development were 12.4 and 12.0°C, respectively. These high thermal thresholds could be a safety mechanism to avoid the emergence of nymphs in the unfavorable winter period. Female weight increased between 15 and 25°C and decreased at 30°C. The fecundity increased from 70.2 eggs per female at 15°C to 212.4 eggs per female at 25°C, and decreased to 88.5 eggs per female at 30°C. Fertility ranged from 9.4% at 15°C to 40.9% at 25°C, being 24.9% at 30°C. The intrinsic rate of natural increase (r_m) rose from 0.001 to 0.081 between 15 and 25°C and decreased to 0.05 at 30°C. In summary, this species performs poorly at low temperatures and has a relative tolerance of high temperatures (30°C); its performance was best at 25°C. Knowledge of the variation in the biological parameters with temperature may be very useful for the understanding of its ecology and population dynamics.     

Effect of temperature on reproduction and embryonic development of the cabbage stem flea beetle,Psylliodes chrysocephala L., (Coleoptera: Chrysomelidae)

The cabbage stem flea beetle, Psylliodes chrysocephala (L.) (Coleoptera: Chrysomelidae), is a major pest of winter oilseed rape. Despite the importance of this pest, detailed information on reproduction to predict risk of crop damage is lacking. This study investigates the effect of temperature on parameters of reproduction, egg development and viability at five constant temperatures. Significant temperature effects were found on the pre‐oviposition period, total number of eggs laid, daily oviposition rate, female longevity, egg‐development rate and viability. The mean length of the pre‐oviposition period ranged from 93.1 days at 4°C to 14.6 days at 20°C. Analysis of total number of eggs laid and daily oviposition rate during female lifespan estimated the highest total number of eggs laid (696 eggs/female) at 16°C and the highest oviposition rate (6.8 eggs/female and day) at 20°C. The daily oviposition rate at 20°C was not significantly higher than 5.4 eggs/female and day at 16°C. Female longevity was significantly longer at 4°C, shorter at 20°C and not significantly different between 8, 12 and 16°C. Estimated 50% survival time of females was 239, 153, 195, 186 and 78 days at 4, 8, 12, 16 and 20°C, respectively. A linear model of egg development at 8–20°C estimated the lower developmental threshold to be 5.1°C and the thermal constant for development 184.9 degree‐days. The percentage of eggs hatching was significantly lower at 4°C than at all other temperatures tested. The estimated mean hatching percentages were 47.3%, 70.0%, 72.4%, 66.2% and 67.9% at 4, 8, 12, 16 and 20°C, respectively. These results can be used to predict the start and intensity of egg‐laying in the autumn and the appearance of larvae in the field from knowledge about time of field invasion and from monitoring the weather.     

Zur fortpflanzungsbiologie von mesostoma ehrenbergii (Focke, 1836) (Turbellaria)

1. At temperature levels from 10 to 25°C animals from resting eggs produce subitaneous eggs independent on temperature. In contrast animals from subitaneous eggs produce subitaneous eggs dependent on temperature. At a high rate subitaneous eggs are only formed at temperature levels above 20°C.
2. Below 10°C no development occurs in the juveniles. At temperatures of 30/22°C (24.7°C) the first subitaneous eggs are formed after 6–9 days, at 14/9°C (10.7°C) they are formed after 34 days. At different temperature levels the developmental rate of the young is from 10.5 to 42 days. One generation extends over 16.5 (30/22°C) to 75 days (14/9°C). The average egg production is 10–20 subitaneous eggs or 30–60 resting eggs. The maximum egg production of one individual is 50 subitaneous eggs or 84 resting eggs. 50% of the animals have just formed resting eggs, before the juveniles are hatched. Resting eggs in the first egg-batch are formed 6–20 days later than subitaneous eggs. The duration of life is between 65 (30/22°C) and 140 days (19/13°C).
3. Young worms in resting eggs have a dormance period of at least 15–30 days.

At room temperatures (20°C) no juvenile in resting eggs hatches from water. By combining room and refrigerator (3.5°C) temperatures the hatching rate increases to a maximum of 85%. To reach a hatching rate of 50–65% the influence of low temperatures must be at least 30 days. At room temperatures 60% of the young in resting eggs hatch from mud covered with water. Combining high and low temperatures the hatching success is between 67 and 81%, where the highest percentage of the young may hatch at room temperature. Up to 90 days low temperatures cause a maximum hatching rate of 79%. It decreases to approximately 30% after 180 days. At high temperatures resting eggs preserved in 100% moist mud, survive for two months. By adding a period of low temperatures the hatching rate increases to a maximum of 52%. Low temperatures are survived for more than 6 months. Up to 30 days preservation at 3.5°C causes a maximum hatching rate of 61%, up to 12o days it decreases to 30%. At room temperature the young in resting eggs are not resistant against air-dried mud (30–40% rel. air moisture). Combining high and low temperatures air-dried mud is endured 1 month (hatching rate 5–14%). Preservation of 30–120 days at 3.5°C and 70% rel. air moisture result in a hatching rate of 43–61%. li]4. In the open air in Middle-Europe there occur 5–6 generations of M. ehrenbergii per life-cycle. The first generation hatches from resting eggs in May, where the production of subitaneous eggs is independent on temperature. All other generations up to October hatch from subitaneous eggs. The egg-production of those worms is dependent on environmental factors. In summer subitaneous egg production prevails, in autumn resting egg production. The abundance during the life-cycle is dependent on the number of animals which produce subitaneous eggs. Resting eggs are predestinated to endure periods of dryness and cold. The life-cycles of the species M. lingua and M. productum are different from those of M. ehrenbergii in length and in the number of generations. In both species 7 generations occur over 8 to 8.5 respectively 5.5 months. M. nigrirostrum only forms resting eggs. The life-cycle consists of one generation from February/March to May/June.     

Effects of temperature experienced during embryonic development on biomass and C and N composition at hatching in Palaemon serratus (Pennant, 1777)

In decapod crustaceans, the conditions experienced during embryonic development trigger phenotypic plasticity of the larvae at hatching. The objective of this study was to test the effects of temperature during embryonic development of Palaemon serratus on the phenotypic plasticity of hatching larvae. We incubated egg-bearing females from eggs laying to hatching at four temperatures (10, 15, 18 and 20°C). Weight, carbon and nitrogen contents were measured on newly laid eggs and on freshly hatched larvae. The duration of embryonic development was negatively correlated with incubation temperature. At 20°C, all females abandoned their eggs during development. Incubation temperature had no effect on the weight and the percentage of N of the larvae at hatching, while it did affect their percentage of C and their C/N ratio. Embryos incubated at 10°C seemed to produce larvae with fewer lipid reserves than those incubated at 15 and 18°C. They probably overconsumed their lipid reserves to compensate for the metabolic losses due to the low temperature. These results provide information on the link between maternal investment per egg and larval development in P. serratus.     

Development of two forensically important blowfly species (Chrysomya megacephala and Chrysomya rufifacies) (Diptera: Calliphoridae) at four temperatures in India

The development of the Oriental latrine fly, Chrysomya megacephala (Fabricius), and hairy maggot blowfly, C. rufifacies (Macquart) (Diptera: Calliphoridae), was studied at four different temperatures (22°C, 25°C, 29°C and 31°C) in order to draw correlations between larval age, body length and body dry weight. The mean larval body length increased steadily from a minimum of 1.4 mm for C. megacephala and 1.8 mm for C. rufifacies to a maximum of 17.4 mm for C. megacephala and 15.9 mm for C. rufifacies at different temperatures. Similarly, the mean dry weight increased steadily from a minimum of 0.0007 g for C. megacephala (second instar) and 0.0008 g for C. rufifacies (second instar) to a maximum of 0.0290 g for C. megacephala and 0.0270 g for C. rufifacies at different temperatures. Entomological evidence is often used to estimate the minimum postmortem interval (mPMI) and both of these species are important from a forensic point of view. Graphs of age of larvae vs. body length and age of larvae vs. dry body weight at different temperatures can be used to estimate the larval age of these two species.     

Temperature‐dependent development of the parasitoid Tachinaephagus zealandicus on five forensically important carrion fly species

The influences of temperature and host species on the development of the forensically important parasitoid Tachinaephagus zealandicus Ashmead (Hymenoptera: Encyrtidae) were studied at six constant temperatures in the range of 15–30°C. T. zealandicus completed development successfully between 15°C and 27°C on five species of Calliphoridae, Calliphora albifrontalis Malloch, Calliphora dubia Macquart, Lucilia sericata Meigen, Chrysomya rufifacies Macquart and Chrysomya megacephala Fabricius. No adult parasitoids emerged from any of the host species reared at 30°C. Temperature and host species significantly influenced development time, emergence success and progeny size. Development was significantly longer on Ch. megacephala and Ch. rufifacies at 18–24°C and significantly longer on Ch. rufifacies and C. albifrontalis at 15°C and 27°C. Parasitoid emergence success was greatest at 21°C, declined at the temperature extremes (15°C and 27°C) and was significantly lower on Ch. megacephala and Ch. rufifacies than on the three other host species. Progeny numbers per host pupa were highest at 21–24°C, declined on either side of this temperature range and were significantly lower on L. sericata, Ch. rufifacies and Ch. megacephala than on either C. dubia or C. albifrontalis. An effect of host species on sex ratio was only observed at 27°C, at which a higher proportion of T. zealandicus females emerged from Ch. megacephala and Ch. rufifacies than from the other host species. The thermal requirements for development (developmental thresholds, thermal constant, optimum temperature) of T. zealandicus in each host species were estimated using linear and non‐linear models. Upper and lower developmental thresholds ranged between 29.90°C and 31.73°C, and 9.73°C and 10.08°C, respectively. The optimum temperature for development was estimated at between 25.81°C and 27.05°C. Given the significant effect of host species on development time, the use of parasitoid–host‐specific developmental data in forensic application is recommended.     

Temperature dependence for development of the whitefly predator <Emphasis Type="Italic">Clitostethus arcuatus</Emphasis> (Rossi)

This work aimed to study the biology of Clitostethus arcuatus (Rossi) (Coleoptera: Coccinellidae) under different temperatures and evaluate the optimum temperature for its mass rearing. Studies were carried out in the laboratory at four constant temperatures (15°C, 20°C, 25°C and 30°C), 75 ± 5% relative humidity and a photoperiod of 16 h light:8 h dark, in which C. arcuatus was fed ad libitum with nymphs of all instar of Aleyrodes proletella L. (Homoptera: Aleyrodidae) on Brassicae oleracea L. (var. Costata). The following biological parameters were evaluated: development time and survival rates of pre-imaginal stages, adult longevity (female and male), length of the pre-oviposition and oviposition periods, fecundity, fertility and percentage of egg hatching. Population growth parameters, the lower development threshold and the sum of effective temperatures were estimated. Temperatures ranging from 20°C to 30°C were suitable for the development of C. arcuatus, suggesting that this species is well adapted to the temperatures usually found inside greenhouses or in open fields in temperate regions. Although the intrinsic rate of natural increase and doubling time were similar at 25°C and 30°C, the temperature of 25°C was shown to be the most suitable for mass rearing and development of populations under field conditions, since the percentage of egg hatching and the accumulated survival rates of the pre-imaginal stages were the highest. Considering the estimated lower threshold for pre-imaginal development (7.9°C) and the sum of effective temperatures [293.6 degree-days (°D)], it is predicted for Ponta Delgada (Azores, Portugal) that the first adults of C. arcuatus should emerge by the first fortnight of February and that up to 12 generations per year can occur.     

Influence of temperature and light–dark cycle on hatching of <Emphasis Type="Italic">Eylais extendens</Emphasis>

Little research has been done on egg diapause and the embryonic development of water mites. The aim of this study was to check the impact of temperature and periods of light on hatching of larvae of Eylais extendens. Three batches of eggs which were spawned on 30 July were placed at one of three temperatures (4, 10 and 20 °C) and two periods of light (7 and 14 h per day). Egg hatching (both, percentage of hatched larvae and rate of hatching) was found to differ between 4 versus 10 °C and between 4 versus 20 °C, but not between 10 versus 20 °C. The periods of light had no influence on hatching. This synchronization of hatching, enabling the eggs to emerge from diapause in the spring, could be considered an evolutionary adaptation aimed at postponing hatching of late-spawned eggs until a time allowing for completion of the full development cycle, including the parasitic larval stage.     

Incubation temperature affects hatching success,embryonic expenditure of energy and hatchling phenotypes of a prolonged egg-retaining snake,Deinagkistrodon acutus (Viperidae)

We used eggs of Deinagkistrodon acutus to study the effects of incubation temperature on hatching success, embryonic expenditure of energy and hatchling phenotypes. One egg from each of the 15 fertile clutches was dissected for determination of egg composition, and a total of 164 eggs were incubated at five constant temperatures. Embryonic mortality increased dramatically at 30 °C, and none of eggs incubated at 32 °C hatched. Within the range from 24 to 30 °C, temperature affected incubation length and most hatchling traits examined. The mean incubation length at 24, 26, 28 and 30 °C was 36.4, 28.7, 21.8 and 15.7 days, respectively. Embryos developing at higher temperatures (28 and 30 °C) consumed more energy but produced less developed (and hence smaller) hatchlings, which characteristically had larger residual yolks but smaller carcasses. A principal component analysis resolved two components (with eigenvalues ⩾1) from ten size (initial egg mass)-free hatchling variables, accounting for 79.3% of variation in the original data. The first component (43.8% variance explained) had high positive loading for size-free values of dry mass, lipid mass, energy contents and ash mass of hatchlings, and the second component (35.5% variance explained) had high positive loading for size-free values of SVL, carcass dry mass and fatbody dry mass. Hatchlings from different incubation temperatures did not differ in scores on the first axis of the principal component analysis, whereas hatchlings from higher incubation temperatures (28 and 30 °C) had significantly lower scores on the second axis than did those from lower incubation temperatures (24 and 26 °C). As the second axis mainly represents traits relating to the developmental condition at hatching, the analysis therefore provided further evidence that eggs incubated at higher temperatures produced less developed hatchlings. Taken together, our data show that the optimal temperatures for embryonic development are relatively low in D. acutus largely due to its use of relatively cool habitats.     

THE EFFECT OF CONSTANT TEMPERATURES ON THE HATCHING OF EGGS AND SURVIVAL OF THE FRESHWATER SNAIL BIOMPHALARIA GLABRATA (SAY)

SUMMARY

The incubation period and percentage hatching of eggs of pigmented and unpigmented Biomphalaria glabrata at constant temperatures were investigated in the range 14 °C to 34 °C. In order to determine the influence of extreme temperatures on adult snails, specimens of the same species were exposed to 0 °C and 40 °C for selected time periods. The results indicate that sustained temperatures below 16 °C and above 32 °C are detrimental to the development and hatching of B. glabrata embryos. The optimum temperatures for incubation period and hatching differ from each other. As far as temperature is concerned, this foreign snail species should be capable of successfully colonizing the warmer parts of southern Africa.     

Influence of temperature and photoperiod on embryonic development in the dragonfly Sympetrum striolatum (Odonata: Libellulidae)

Temperature and photoperiod play major roles in insect ecology. Many insect species have fixed degree‐days for embryogenesis, with minimum and maximum temperature thresholds for egg and larval development and hatching. Often, photoperiodic changes trigger the transfer into the next life‐cycle stadium. However, it is not known whether this distinct pattern also exist in a species with a high level of phenotypic plasticity in life‐history traits. In the present study, eggs of the dragonfly Sympetrum striolatum Charpentier (Odonata: Libellulidae) are reared under different constant and fluctuating temperatures and photoperiodic conditions in several laboratory and field experiments. In general, and as expected, higher temperatures cause faster egg development. However, no general temperature or light‐days for eyespot development and hatching are found. The minimum temperature thresholds are distinguished for survival (2 °C), embryogenesis (6 °C) and larval hatching (above 6 °C). Low winter temperatures synchronize hatching. Above 36 °C, no eyespots are visible and no larvae hatch. In laboratory experiments, light is neither necessary for eyespot development, nor for hatching. By contrast to the laboratory experiments, the field experiment show that naturally changing temperature and photoperiod play a significant role in the seasonal regulation of embryonic development. The post‐eyespot development is more variable and influenced by temperature and photoperiod than the pre‐eyespot development. This developmental plasticity at the end of the embryogenesis might be a general pattern in the Libellulidae, helping them to cope with variation in environmental conditions.     

Effects of short-term heat stress on the growth and development of Bradysia cellarum and Bradysia impatiens

Bradysia cellarum Frey and Bradysia impatiens Johansen are major pests of vegetable crops, as well as edible mushrooms and ornamental plants, and damage to hosts resulting in economic losses. Temperatures above the optimum levels for these pests have been predicted to regulate their population growth during summer. The aim of the present study was to examine the effects of both heat stress and exposure time on the growth and development of eggs, larvae and pupae for two Bradysia species. The egg stage, egg hatching rate, 4th instar larval stage, pupation rate, pupal stage and adult emergence rate were observed after exposing at high temperatures of 34°C, 37°C and 40°C for 1, 2, 4 and 6 hr. The results showed that 34°C, 37°C and 40°C for 1-, 2-, 4- and 6-hr exposure treatments prolonged the developmental stage of egg, 4th instar larva and pupa, while decreasing the egg hatching rate, pupation rate and adult emergence rate. This suggests that increasing temperature or prolonging exposure time to the heat stress could significantly affect insect survival, growth and development. Our study could provide an ecological basis for pests’ management strategy by using short-term heat stress.     

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.     

Modeling egg development of the pest Clavipalpus ursinus (Coleoptera: Melolonthidae) using a temperature‐dependent approach

Abstract Predicting the population dynamics of insects in natural conditions is essential for their management or preservation, and temperature‐dependent development models contribute to achieving this. In this research the effects of temperature and soil moisture content on egg development and hatching of Clavipalpus ursinus (Blanchard) were evaluated. The eggs were exposed to seven temperature treatments with averages of 7.2, 13.0, 15.5, 19.7, 20.6, 22.0 and 25.3°C, in combination with three soil moisture contents of 40%, 60% and 80%. A linear and two non‐linear (Lactin and Briere) models were evaluated in order to determine the thermal requirements of this developmental stage. Temperature affected significantly the time of development and egg hatching, while no significant effect was observed for moisture content. Thermal requirements were set as: 7.2°C for lower developmental threshold, 20.6°C for optimum developmental threshold, 25.3°C for maximum temperature and 344.83 degree‐days for the thermal constant. The linear model described satisfactorily egg development at intermediate temperatures; nevertheless, a slightly better fit of the observed data was obtained with the Lactin model. Egg development took place inside a narrow range of temperatures. Consequently, an increment of soil temperature could generate a negative impact on the population size of this species or changes in its biological parameters.     

Temperature effects on egg development of the rosy apple aphid and forecasting of egg hatch

The development of Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) winter eggs was studied at six different constant temperatures ranging from 7.5 to 16.5 °C in order to improve the basis for phenological forecasts in early spring. The mortality was generally low at temperatures below 13.5 °C but increased considerably at 16.5 °C. The effect of temperature on development rates could be described with linear regression within the temperature range under study. The lower temperature threshold for development was estimated to be 4.0 °C and the thermal constant 140 day‐degrees. A time‐varying distributed delay approach was used to establish a temperature driven phenology model for winter egg hatch of D. plantaginea considering the intrinsic variability in development time. The model parameters such as temperature‐dependent development times and corresponding variances were quantified based on the experimental data. When compared with independent observations on egg hatch under semifield conditions, the model gave satisfactory validation results. It can be used as forecasting tool for the optimal timing of monitoring and control measures for D. plantaginea in early spring.     

Response of diapausing eggs hatching to changes in temperature and the presence of fish kairomones

It has been hypothesized that the production of diapausing eggs in Daphnia can be induced by fish kairomones. A population of Daphnia could survive severe predation using this predator avoidance strategy. However, in changing environments, diapausing eggs experience various temperature conditions, and hatchlings at emergence may be exposed to the same predation risks as their mothers. Therefore, staying in diapause or an immediate response upon hatching to available environmental information could be important for hatchling survival. For this study, we investigated the impact of water temperature (10, 15, 20, and 25°C) in the presence and absence of fish kairomones (Lepomis macrochirus) on the hatching success of resting eggs (D. galeata). Results show that no diapausing eggs hatched at the lowest temperature (10°C), and the highest hatch percentage occurred at 15°C. Although higher water temperatures reduced hatching success, diapausing eggs hatched more quickly. The number of hatchlings was significantly higher after exposure to fish kairomones, and this was more noticeable at higher temperatures (20 and 25°C). The present results suggest that the diapausing eggs were produced as a predator avoidance strategy in Daphnia; however, the presence of fish works as a positive signal to increase hatchlings when the diapausing stage is terminated.     

The effect of temperature on the development times of eggs,naupliar and copepodite stages of five species of cyclopoid copepods

The duration times of eggs, combined naupliar instars and of the different copepodite stages of five species of cyclopoid copepods — Acanthocyclops robustus, Cyclops vicinus, Diacyclops bicuspidatus, Mesocyclops leuckarti, and Thermocyclops crassus — were investigated at five different temperatures. The five species can be divided in two groups: two species, C. vicinus and D. bicuspidatus, adapted to cold water conditions and three species, A. robustus, M. leuckarti and T. crassus adapted to warm water conditions. The cold water species showed a faster egg development than M. leuckarti and T. crassus at 5–15 °C. The eggs and instars of the warm water species M. leuckarti tend to develop faster than those of the former two species at higher temperatures. A. robustus showed the shortest egg and instar development at 10–25 °C. The warm water species T. crassus produced no eggs at 10 °C and temperatures below. At higher temperatures (20, 25 °C) the egg and instar duration times were similar or longer than those of the other species. When cultured in total darkness a great part of the C_IV respectively C_V copepodites of the summer forms entered arrest and the percentage of copepodites that showed an arrest of development was highest at lowest temperatures. The present results are compared with data from literature and differences are discussed.     

Hatching of Daphnia sexual eggs. II. The effect of age and a second stimulus

• 1 We examined the effect of age on the hatching response of Daphnia magna sexual eggs of specific families. For old eggs (>2 years), hatching characteristics were compared at two storage temperatures (4°C and 20°C). Also, the hatching response after a second dark incubation and subsequent incubation under conditions favourable for hatching was compared with that after the first stimulus.
• 2 Daphnia sexual eggs were found to remain viable for several (at least 4.5) years. The effect of age on the hatching rate was family dependent. At least in some families, hatching rate was higher for old (>2 years) than for young (<5 months) eggs. Low temperature (4°C) during dark incubation resulted in a higher hatching rate compared with incubation at 20°C.
• 3 The application of a second hatching stimulus resulted in a renewed hatching response. The overall hatching rate after the second stimulus was, however, lower than that of the first stimulus.
• 4 More than 80% of the hatchlings of young eggs appeared on Day 3 or 4, with minor between-family differences in time distribution of hatching. The timing of the response to hatching stimuli was more variable in old than in young eggs, with the average time at hatching being 6.4 instead of 4.0 days. The response to the application of hatching stimuli was also slower after the second stimulus compared with the first stimulus.