Variable egg development of Dinocras spp. (Plecoptera, Perlidae) and the stonefly seed bank theory

1. Temperature dependence of egg development of Dinocras cephalotes (Curtis) (three German and one Norwegian population) and Slovenian D. megacephala (Klapálek) was studied under a constant 14 : 10 light : dark photoperiod and constant temperature ranges of 4–24 °C and 4–18 °C, respectively. D. cephalotes was also incubated under seasonal field conditions; natural daylength and fluctuating temperatures had no modifying effect. 2. Both species have very similar lower threshold temperatures (4 and 3.5 °C, respectively), thermal demand for development (c. 600 degree days) and high dependence of mean incubation period on temperature (exponents of regressions near 1.5). Present data on D. cephalotes agree with the literature on British and Norwegian material of the same species. 3. Development occurs only at cue temperatures above the lower threshold. Cue temperatures range from 6 °C (some D. megacephala) to 14 °C (some D. cephalotes) and vary strongly within and between egg masses of D. cephalotes. Variation is not random, but seems to be genetically determined. 4. The variable temperature response renders study of effects of particular experimental regimes, and comparisons between local populations, difficult. 5. A latitudinal gradient in cue temperatures for development from 6 °C at c. 46 °N to 12 or even 14 °C at c. 61 °N seems to reflect reduced diversity at high latitudes. 6. Average success of spontaneous hatching exceeded 90% between 12 and 20 °C, but declined towards higher and lower temperatures. 7. Unhatched eggs were not dead but in parapause; development at other, higher or lower, temperatures was induced. Spontaneous plus induced hatching success approached 90%. Developing eggs rarely died; most dead eggs were apparently unfertilized. 8. Dormant plecopteran eggs are proposed to form a seed bank in stream bed sediments. Highly successful development after up to 220 days of dormancy was ascertained in Dinocras, and survival for up to 3 years is reported for other Perloidea. 9. Only systellognathan egg morphology provides options for long dormancy; the other plecopteran superfamilies, notably Nemouroidea, follow different strategies.     

Induction of adult diapause and of low and high reproductive states in a parasitoid wasp,Ooencyrtus nezarae, by photoperiod and temperature

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was reared on eggs ofRiptortus clavatus (Thunberg) (Heteroptera: Alydidae) at various temperatures under long-day (L16:D8) or short-day (L10:D14) conditions. There was no diapause during egg, larval or pupal stages under any set of conditions examined. However, at 15°C under short-day conditions, vitellogenesis was arrested in all adult females and they entered diapause. At 15°C under long-day conditions, or at 20°C under short-day conditions, some adult females entered diapause. Under the latter set of conditions, the adult females laid eggs but they laid fewer eggs than under long-day conditions, Even at 25°C, under short-day conditions, adult females laid fewer eggs than under long-day conditions, and this low rate of oviposition was attributed to the retarded development of ovaries. Diapause adults reared at 15°C were more resistant to low temperature than nondiapause adults reared at 25°C.     

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.     

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.     

Effects of incubation temperature on the energetics of embryonic development and hatchling morphology in the Brisbane river turtle Emydura signata

Incubation temperature and the amount of water taken up by eggs from the substrate during incubation affects hatchling size and morphology in many oviparous reptiles. The Brisbane river turtle Emydura signata lays hard-shelled eggs and hatchling mass was unaffected by the amount of water gained or lost during incubation. Constant temperature incubation of eggs at 24 °C, 26 °C, 28 °C and 31 °C had no effect on hatchling mass, yolk-free hatchling mass, residual yolk mass, carapace length, carapace width, plastron length or plastron width. However, hatchlings incubated at 26 °C and 28 °C had wider heads than hatchlings incubated at 24 °C and 31 °C. Incubation period varied inversely with incubation temperature, while the rate of increase in oxygen consumption during the first part of incubation and the peak rate of oxygen consumption varied directly with incubation temperature. The total amount of oxygen consumed during development and hatchling production cost was significantly greater at 24 °C than at 26 °C, 28 °C and 31 °C. Hatchling mass and dimensions and total embryonic energy expenditure was directly proportional to initial egg mass. Accepted: 18 March 1998     

Female reproductive cycles in the northernmost populations of the two gekkonid lizards,Hemidactylus frenatus andLepidodactylus lugubris

Lepidodactylus lugubris, a parthenogenetic gekkonid lizard of possible tropical origin, occurs on Kita-Daitojima Island of the Ryukyu Archipelago and lays eggs almost throughout the year. The oviposition season of the sympatric population of another primary tropical, but bisexual gecko,Hemidactylus frenatus, is confined to between April and September. Laboratory experiments indicate that the hatching ratio of the egg reduces with the decrease of incubation temperature in both species. Some eggs ofL. lugubris develop at 14°C of ambient temperature, wheras eggs ofH. frenatus always die at temperatures of 18°C or lower. Examinations of stomach contents and fat body mass in the monthly samples suggest that food availability is not severely low for the geckos even during the winter, rejecting the previous assumption that food stress suppresses vitellogenesis inH. frenatus. No other environmental factors that may induce reproductive seasonality as phenotypic physiological responses were detected either. Tropical populations ofH. frenatus andL. lugubris are known to lack distinct annual reproductive cyclicity. Thus, it is probable that the East AsianH. frenatus has evolved the winter quiescence of reproduction, presumably due to the poor embryonic tolerance of low temperatures. The absence of such seasonality in the sympatricL. lugubris seems to be attributable to its clonal nature which predicts the low genetic variability of the population from the colonization stage.     

Temperature‐mediated survival,development and hatching variation of Pacific cod Gadus macrocephalus eggs

Laboratory‐validated data on the survival, development and hatching responses of fertilized Pacific cod Gadus macrocephalus eggs from the northern Japan stock were determined through an incubation experiment. The optimum temperature for survival until hatching ranged from 4 to 8° C. No significant difference in development rates was found between the populations from Mutsu Bay, Japan, and western Canadian coastal waters even though the samples may belong to different G. macrocephalus stocks. Gadus macrocephalus larvae hatched asynchronously from egg batches despite incubation under the same environment during their development. Both incubation temperature and temperature‐mediated hatch rank affect size and yolk reserve. These data suggest that variations in water temperatures within an ecological range markedly influence the development rates, survival and hatching of the eggs, as well as the stage at hatch larvae of G. macrocephalus. Asynchronous hatching and the production of offspring with variable sizes and yolk reserves are considered evolutionary bet‐hedging strategies that enable the species to maximize their likelihood of survival in an environment with variable temperatures.     

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.     

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.     

Artificial incubation of California condor Gymnogyps californianus eggs removed from the wild

The currrent California condor (Gymnogyps californianus) recovery plan entails increasing the reproductive rate via replacement-clutch manipulation of eggs. During the period from 1983 to 1985, 15 eggs were removed from wild nesting pairs for artificial incubation. The eggs were incubated at a dry bulb temperature of 36.4°C in modified forced-air Lyon Electric incubators. The incubation humidity was adjusted for individual eggs based on weight loss data (water = weight), 25.6–30.0°C wet bulb (41.0–63.0% Relative Humidity (RH)). The chicks were hatched initially under forced-air conditions of 36.1°C dry bulb, 31.1–01.7°C wet bulb (70.0–73.0% RH). In 1984, hatching parameters were changed to still-air conditions, 36.1°C dry bulb (top of the egg), 35.0°C dry bulb (bottom of the egg), 31.1–31.7°C wet bulb (70.0-73.0% RH). Tactile and auditory stimulation was utilized during the pip-to-hatch interval. From among 15 eggs collected, 13 hatched, and 12 condor chicks were raised successfully (hatchability: 86.7%; survivability: 92.3%).     

SOME PHYSICAL REQUIREMENTS FOR OSTRICH EGG INCUBATION

Jarvis, M. J. F., Keffen, R. H. & Jarvis, C. 1985. Some physical requirementsfor Ostrich egg incubation. Ostrich 56: 42–51.

Eggs from wild and domesticated Ostriches Struthio camelus australis were studied to determine temperature and humidity requirements for successful incubation. Wild eggs in Zimbabwe included some collected and incubated artificially, and others that were naturally incubated until just before hatching. Egg-weight losses during incubation were measured. The eggs artificially incubated at 35 °C to 36°C and 40–42% relative humidity, lost nearly the same weight as did eggs in naturally incubated nests. Comparisons were made between the wild eggs and chicks, and those from domesticated hybrid-strain Ostriches in Bophuthatswana. The discussion outlines some of the remaining problems associated with Ostrich egg incubation.     

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.     

Effect of constant temperatures on development of the walnut husk fly,Rhagoletis completa

The developmental rates of various life stages ofRhagoletis completa Cresson (Diptera: Tephritidae) were determined in the laboratory at seven different constant temperatures: 8, 12, 16, 20, 24, 28, and 32±1°C, RH 80±10%, photoperiod L 16∶D8. Preoviposition developmental rate was fastest at 28°C (10±1 days, mean±SD) and slowest at 12°C (26±1 days). About 83% of the females deposited eggs at 20 and 24°C and only 25% oviposited at 32°C. Females laid the highest number of eggs at 24°C and the lowest at 8°C. Egg development increased with increasing temperatures up to 28°C, then declined. The fastest egg development was noticed at 28°C (55±1 h) and slowest at 8°C (389±2 h). Over 90% egg hatch was observed at temperatures between 12 and 32°C, but decreased to 73% at 8°C. Larval development was fastest also at 28°C (20±0.2 days). Over 65% pupation was recorded at 20 and 24°C, but decreased to 15% at 32°C and 12% at 8°C. Pupal development was most rapid at 24°C (53±1 days) and slowest at 8°C (162±2 days). More than 70% of adult emergence was noticed in treatments between 16 and 24°C but decreased to 20% at 8°C. Based on a linear regression model of temperature-development rate relationship, the lower developmental thresholds were determined to be 6.6, 5.3, 2.9, and 5°C for preoviposition, egg, larval, and pupal stages, respectively. Based on a non-linear developmental rate model, the upper developmental thresholds were 34°C for preoviposition, egg, and larval stages and 30°C for pupal stage.     

In situ Development of Perch Eggs,Perca fluviutilis L. (Pisces,Percidae) in a Small Eutrophic Lake,Lake Plussee,Holstein, Germany

Naturally spawned egg strands of perch, Perca fluviatilis L. were sampled from exposed fir trees submerged in Lake Plußsee, Holstein, Northern Germany from April to May 1989. These were incubated in situ and in the laboratory to estimate the viability, development and abnormalities of the embryos. From the in siru incubated eggs 91.6% embryos were viable, the nonviable portion comprising 1.1 % unfertilized eggs, 5.1 % dead and 2.2 % with abnormalities. As compared to the eggs incubated in the laboratory with 84.1 % viable embryos, the nonviable portion consisting 1.1 % unfertilized eggs, 11.3 % dead and 3.5 % with abnormalities. Incubation rate of P. fluviatilis embryos both in situ and laboratory, ranged from 200-210 ATUs (10°C in situ and 8°C in the laboratory) with incubation period of 20-27 days from fertilization to 50 % hatching.     

Effects of down collection on incubation temperature, nesting behaviour and hatching success of common eiders (Somateria mollissima) in west Iceland

Incubating common eiders (Somateria mollissima) insulate their nests with down to maintain desirable heat and humidity for their eggs. Eiderdown has been collected by Icelandic farmers for centuries, and down is replaced by hay during collection. This study determined whether down collecting affected the female eiders or their hatching success. We compared the following variables between down and hay nests: incubation temperature in the nest, incubation constancy, recess frequency, recess duration, egg rotation and hatching success of the clutch. Temperature data loggers recorded nest temperatures from 3 June to 9 July 2006 in nests insulated with down (n = 12) and hay (n = 12). The mean incubation temperatures, 31.5 and 30.7°C, in down and hay nests, or the maximum and minimum temperatures, did not differ between nest types where hatching succeeded. Cooling rates in down, on average 0.34°C/min and hay nests 0.44°C/min, were similar during incubation recesses. Females left their nests 0–4 times every 24 h regardless of nest type, for a mean duration of 45 and 47.5 min in down and hay nests, respectively. The mean frequency of egg rotation, 13.9 and 15.3 times every 24 h, was similar between down and hay nests, respectively. Hatching success adjusted for clutch size was similar, 0.60 and 0.67 in down and hay nests. These findings indicate that nest down is not a critical factor for the incubating eider. Because of high effect sizes for cooling rate and hatching success, we hesitate to conclude that absolutely no effects exist. However, we conclude that delaying down collection until just before eggs hatch will minimize any possible effect of down collection on females.     

How incubation temperature influences the physiology and growth of embryonic lizards

Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures, being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic production cost of hatchling B. duperreyi (3.52 kJ · g⁻¹) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g⁻¹) than at 25 °C (3.47 kJ · g⁻¹). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling morphology. Accepted: 27 January 2000     

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.

     

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.     

Desiccation and egg viability of the ragwort flea beetle,Longitarsus flavicornis (Coleoptera: Chrysomelidae)

A study was conducted to investigate the effect of desiccation on the survival of eggs of Longitarsus flavicornis. Eclosion of L. flavicornis eggs in laboratory trials decreased with increasing desiccation time between 0 days (93% hatching) and 42 days (no egg hatching) at 50±2% relative humidity and 23±2°C. Probit analysis indicated that 25, 50 and 99% mortality of L. flavicornis eggs occurred after 5.7, 9.3 and 50.4 days desiccation, respectively. Egg development varied between a minimum of 8 days at 7 days desiccation to a maximum of 15 days at 28 days desiccation. Hatching span did not differ between treatments with all eggs hatching within 12 days of each other. A relative humidity of 88–100% was measured under ragwort rosettes in non-drought field conditions. This would be expected to facilitate successful egg eclosion. However, the occurrence of summer drought could be detrimental to egg survival.     

Influence of temperature on hatching of winter eggs of fruit-tree red spider mite, Panonychus ulmi (Koch)

The effects of the duration and degree of chilling, and the temperature of incubation, on hatching of winter eggs of Panonychus ulmi (Koch) were investigated. For chilling, 0°C and 5°C were more effective than — 5° and 9°, and the limits for the reaction were close to — 10° and 15°. As the chilling period was increased from 60 to 200 days, the percentage hatch on incubation at 21° increased, and the mean incubation time and its variance decreased. Before the maximum effect of chilling was achieved, percentage hatch on incubation at 9° and 15° was higher than at 21°; 27° was lethal to most winter eggs though not to summer eggs. After chilling, the later stages of diapause development could occur at temperatures from 0° to 21°₎ i.e. above and below the threshold temperature for morphogenesis, 6–7° in both winter and summer eggs. Diapause development cannot, therefore, be a unitary process. The significance of the results is discussed in relation to forecasting the time of hatch in the field, and to the phenological aspects of hatching in the spring.