Influence of photoperiod on low temperature acclimation for cold-hardiness in Drosophila auraria

ABSTRACT. Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold-hardiness at low temperatures to a greater extent when exposed to a diapause-inducing photoperiod (LD10:14 h) than when exposed to a diapause-preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to -5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post-diapause females the ability to develop cold-hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non-diapause females. These results suggest that the physiological mechanism which promotes cold-hardiness under a diapause-inducing photoperiod is not directly linked to the process causing reproductive diapause.
In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.     

Synchronization of larval emergence in winter moth (Operophtera brumata L.) and budburst in pedunculate oak (Quercus robur L.) under simulated climate change

1. The hypothesis that a 3 °C elevation in temperature and doubled CO₂ concentration would have no effect on the synchronization of winter moth egg hatch with budburst in oak was tested by comparing the separate and interactive effects of ambient and elevated (+ 3 °C) temperature and ambient and elevated (doubled to 340 p.p.m.) CO₂ in eight experimental Solardomes. In addition, an outdoor control was compared with the ambient temperature/CO₂ treatment combination.
2. Elevated temperature accelerated darkening (preceding egg hatch by about 5–10 days) and hatching of eggs developing off the trees; elevated CO₂ had no effect. The same effects were observed in eggs developing on the trees.
3. Within treatments, date of egg hatch was the same on trees with early or late budburst.
4. Egg darkening and budburst were closely synchronized at both ambient and elevated temperatures.
5. Both eggs and trees required fewer cumulative heat units (day degrees > 4 °C), for hatching and budburst, respectively, at ambient than elevated temperatures. The requirements in the outdoor control treatment were similar to those in the ambient Solardome treatment.
6. Egg hatch between 10 and 25 °C, on a temperature gradient in the laboratory, required a constant number of heat units; fewer were required below 10 °C.
7. Elevated temperatures, in the Solardomes and the field, delayed adult emergence from the pupae.
8. The results suggest that a general increase in temperature with climatic change would not affect the closeness of the synchronization between egg hatch of winter moth and budburst of oak.     

Geographical variation in egg cold hardiness: a study on the adaptation strategies of the migratory locust Locusta migratoria L.

Abstract. 1. For many species of insect, cold hardiness is an important trait that enables a population to develop in the next season and to extend its range. To elucidate the role of cold hardiness of the migratory locust Locusta migratoria L. in its outbreak and distribution areas, egg cold hardiness was examined in locusts derived from four locations from latitude 18°23'N to latitude 41°10'N in eastern China.
2. The supercooling points of eggs from different geographic populations did not differ significantly for the first development stage, with an average ± SE of −24.5 ± 0.51 °C, or for the second stage, −22.06 ± 0.68 °C, however there was a significant difference for the embryonic development phase among the four geographical populations. The egg supercooling point increased gradually from neonatal egg to old egg; eggs prior to hatching always had a much higher supercooling point.
3. Comparisons of the cold hardiness of four populations were carried out by validating the close correlation between latitude and the effects of cold on hatching, low lethal temperature (Ltemp₅₀), and low lethal time (Ltime₅₀). There were significant differences among the four populations; the northern population was more cold hardy than the southern population, and the two mid-latitude populations were intermediately cold hardy.
4. The cold hardiness of all populations was enhanced to various degrees by short-term cold acclimation at 0 °C and 5 °C. For most populations, a 2-day acclimation period seemed to be optimal.     

Hatching of cladoceran resting eggs: temperature and photoperiod

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

Effects of temperature of adults and eggs on the induction of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus

Abstract.  Eggs laid by adult female Dianemobius nigrofasciatus , reared under long-day (LD 16 : 8 h, 25 °C) or short-day (LD 12 : 12 h, 25 °C) conditions from the nymphal stage, are kept at several constant temperatures. At 22.5–30.0 °C, eggs laid by long-day adults show lower incidences of diapause than those laid by short-day adults. In both eggs laid by adults under long-day conditions and those under short-day conditions, the higher the temperature at which the eggs are kept, the lower the incidence of diapause. When eggs of long-day adults are exposed to a low-temperature pulse (10 °C, 24 h) on the day of deposition (day 0), the incidence of diapause increases. The low-temperature pulse on day 1 does not increase the incidence of diapause. By contrast, when the eggs of short-day adults are exposed to a high-temperature pulse (35 °C, 24 h) on day 0 or day 1, the incidence of diapause decreases. The temperature pulses on day 0 are more effective at diapause prevention. Staining of diapause eggs by the Feulgen–Rossenbeck method shows that the eggs enter diapause at the blastoderm stage, which is on day 1 or day 2 at 25 °C. The exposure of adults to long days and higher temperatures prevents the eggs from entering diapause. In D. nigrofasciatus , embryonic diapause is controlled by maternal effects, adult photoperiod and temperature, and egg temperature before or at diapause.     

Diapause in a Glasgow strain of the flour moth, Ephestia kuehniella

ABSTRACT. The incidence of diapause in Ephestia kuehniella Zeller from an unhealed granary in Scotland was influenced by both photoperiod and temperature. At 25°C, nearly 50% of larvae entered diapause when reared in continuous darkness (DD) and up to 30% did so in short photoperiods. Little diapause was detected around LD 14:10 but a second, smaller peak of about 20% occurred at LD 16:8 and LD 18:6, falling away again to nearly zero in continuous light. More larvae entered diapause when reared continuously at 15 or 20°C than at 25 and 30°C. However, when larvae reared from hatch at 25°C in LD 16:8 were transferred after 1 week to 15°C in LD 9:15, almost twice as many entered diapause as did those reared at 15°C throughout. The sensitive phase for diapause induction occurred near the start of the final instar. The mean duration of diapause was between 2 and 3 months in most photoperiods at 20 and 25°C, and was shorter at 15°C. However, in DD at 25°C, it lasted about 7 months. Termination of diapause was hastened in larvae reared at 25°C in DD by transferring them to LD 14:10, and also by chilling them at 7.5°C for 6 weeks before returning to 25°C in DD. In an unhealed store in southern England, viable adults emerged from May to July and originated from larvae which terminated diapause relatively late. It would appear from the results of transferring larvae back to the laboratory at various times during the winter that some phases of diapause development were completed quite early after exposure to low temperatures, although no further development took place in the store until temperatures rose again in April.     

Overwintering ecology of alpine Collembola and oribatid mites from the Austrian Alps

Abstract. 1. Collembola and oribatid mites from windswept mountain ridges at about 2700 m a.s.l. in the Austrian Alps were all killed by freezing, and depend on supercooling to survive low winter temperatures. The Collembola Tetracanthella afurcata Handschin, Xenylla acauda Gisin and Isotoma spp. collected in January had average supercooling points between -25 and -29°C, and the oribatid mites Fuscozetes fuscipes (Koch) and Lepidozetes singularis Berlese of about -28 and -31°C respectively. The ability to supercool was not increased during storage at -5°C, and was generally lower in species collected in March.
2. The oribatid mites Fuscozetes intermedius Caroli and Maffia, F. fuscipes, Damaeus diversipilis (Willmann) and L.singularis contained from 9 to 16 μg glycerol per mg fresh weight after storage at -5°C, while no glycerol could be detected in the Collembola Isotoma spp., T.afurcata and Onychiurus vontoernei Gisin.
3. Activity below 0°C was observed in T.afurcata and O.vontoernei , which had chill-coma temperatures of -7.7 and -4.9°C respectively.
4. Some specimens of F.intermedius survived more than 90 days of anoxia at 0°C, T.afurcata up to 60 days and O.vontoernei up to 24 days.
5. The overwintering biology of Collembola and oribatid mites from the Austrian Alps appears similar to that of Norwegian species, except that those from Austria have slightly lower supercooling points and higher contents of glycerol.     

Reproductive response of a tropical mammal, the musk shrew (Suncus murinus), to photoperiod

Musk shrews (Suncus murinus) were maintained for 8 weeks in long (16 h light:8 h darkness) or short (8 h light:16 h darkness) daylengths. Males housed in short daylength had significantly lighter androgen-dependent sex accessory organs than did males kept in long daylengths. This same trend was noted in male sexual behaviour. However, the weights of the testes and epididymides and sperm numbers did not differ. Females housed in short daylengths had significantly lighter cervices and were less likely to demonstrate sex behaviour than animals kept in under long daylengths. Ovarian and uterine weights did not differ. These results suggest that the ability to respond to photoperiod can exist in tropical mammals, even if it is not used as a cue to time seasonal breeding.     

Observations on periodicity of hatching of eggs of the potato cyst nematode, Heterodera rostochiensis Woll.

Soil containing new-generation cysts of Heterodera rostochiensis was taken from the field at monthly intervals during late summer and autumn and kept in various conditions for up to a year. The number of eggs that hatched in the stored cysts was compared each month with the number that hatched in cysts taken directly from the field. Eggs did not hatch readily when stimulated during the late autumn and early winter, although more did so in cysts taken from the field before August than after. A few more eggs hatched in cysts stored in air-dried soil than in cysts stored in moist soil. Some cysts were kept at 15 or 20 °C continuously and others at 5, 15 or 30 °C for 6 weeks followed by 20 °C continuously. Storage at 30 °C caused eggs to hatch sooner, but otherwise the temperature of storage had little effect on hatch at any time of the year. Warmth also increased the hatch of H. cruciferae sooner, and some synthetic hatching agents did so with both of these species. When freed from new cysts, more eggs of H. rostochiensis hatched than in intact cysts and hatch was further increased when the fragments of tanned cyst-wall were left with the freed eggs. Puncturing the cyst-wall of new brown cysts had little effect on the hatch in potato root diffusate. Like eggs in new cysts, those in 1-year-old cysts stored out of doors ceased to hatch during the autumn and winter. The term ‘dormancy’ is inadequate to describe the inability of eggs of H. rostochiensis and other Heterodera spp. to hatch in the appropriate stimulant and the term ‘facultative diapause’, as applied to insects, better fits the phenomenon.     

Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae)

The cold-hardiness of Dermacentor marginatus using laboratory-reared offspring of ticks collected in Germany was characterized. Investigations of unfed stages revealed that adult ticks suffered 50% mortality at –10°C after 4–5 months, but larvae and nymphs suffered mortality within few days, whereas –15°C was lethal for all stages within a very short period. Larval hatch and moulting of engorged larvae and nymphs did not occur at 10°C. Embryonic development of eggs with larval hatch was considerably reduced by exposure of eggs to 10°C. Engorged females did not lay eggs at 10°C, the oviposition capability, however, persisted over 6 months at 10°C, 5 months at 5°C, 3 months at 0°C and 2 months at –10°C without substantial decrease of the oviposition capacity or reduction of viable eggs. These results present evidence that unfed adult ticks are the ecoepidemiologically most effective stages, which are capable to tolerate long and extremely cold winters without substantial impairment of the population density. It is also considered that engorged females interrupt their oviposition at low and subzero temperatures delaying it for months and so contribute in bypassing winter conditions. None of the stages survived supercooling indicating that D. marginatus is freeze intolerant. Mean supercooling point (SCP) ranged between –26°C in eggs and –12, 6°C in engorged females. Compared with eggs, the SCP of the other stages was significantly higher. In conclusion, the SCP is considered to have no predictive value in the context with cold-hardiness.     

The fecundity, development and host relationships of Ceratobaeus spp. (Hymenoptera: Scelionidae), parasites of spider eggs

Abstract. 1. Ceratobaeus spp. enter the nest of their host spider and oviposit into eggs through the thin silk eggsac.
2. Temperatures below 15° C limit oviposition by slowing parasites down.
3. Males emerge prior to females and mate with their sibs. Sex ratios of 6.6–6.0:1 in favour of females were observed in the field and laboratory for two species.
4. Even though females can oviposit almost immediately after emergence their full complement of eggs (= 65) is not reached until several days later.
5. Superparasitism is low and appears to occur from subsequent accidental ovipositions. No marking of the external surface of hosts was observed.
6. Parasites overwinter as adults under bark. They do not feed as adults nor do they reabsorb their eggs, but rather oviposit as soon as host eggs become available in spring.
7. Successful oviposition occurs in later stages of host eggs reared at 15° C and 20° C than it does at 25°C. Different rates of development between host and parasite is proposed as an explanation for this phenomenon.
8. The species studied show varying degrees of specificity but each has a dominant host. Location of hosts involves cues from the habitat (bark), silk nests of spiders, and some factor associated with host eggs.     

The effect of light and darkness on hatching in the pomacentrid Abudefduf saxatilis

Synopsis Reports that pomacentrid embryos hatch after dusk are confirmed by photic manipulation of sergeant major eggs. Embryos placed in the dark for 20 minutes or longer prior to their normal hatching after sunset hatched, whereas controls held in light did not hatch. Percent of hatched embryos correlated with increasing exposure to darkness up to one hour after which no further improvement in hatching was observed. Embryos maintained in continuous light during their normal twilight hatching period did not hatch. Also, embryos exposed to 60 minutes of darkness, if interrupted by one minute of light every 10 minutes did not hatch. The percent hatch in dark treatments varied significantly between nests and, in some treatments, correlated negatively with the size of the egg clumps (number of eggs per clump) tested. To initiate hatching in the presence of light required intensities of 0.03 lux or less. These low intensities are not reached until about 20 minutes after sunset on the reef where the embryos occur. We conclude that hatching for some embryos occurs about 30 minutes after sunset but for most is not completed until at least one hour after sunset. Hatching therefore takes place at a time long after potential diurnal fish predators have refuged in the reef structure.     

Temperature effects on embryonic development and the life cycle of Diphyllobothrium dendriticum

Diphyllobothrium dendriticum eggs collected from hamster faeces were incubated at 10 or 20 degrees C, or maintained at 4 degrees C for 11-30 months. On day 65, 20-50% of eggs failed to hatch at 10 degrees C and 42-51% did not hatch by day 21 at 20 degrees C. Our study indicates that eggs begin to hatch in mid-August and persist until October in many lakes within the natural range of D. dendriticum. Our results demonstrate that eggs stored at 4 degrees C will hatch, suggesting they can persist in the environment for long periods and contribute to the D. dendriticum life cycle in high Arctic lakes by hatching months or years after release.     

Seasonal variation in the cold-hardiness of a free-living predatory antarctic nematode,Coomansus gerlachei (mononchidae)

Summary Coomansus gerlachei shows a strong seasonal variation in its supercooling ability, with most individuals freezing between -5° and -7°C, in a discrete high group, or between -15° and -26°C in a more diffuse low group. Increased cold-hardiness in winter is achieved by a strategy of freeze avoidance with an increase in the proportion of the population showing extensive supercooling ability. Smaller life-stages also exhibit lower supercooling points. Ice-nucleation at high sub-zero temperatures increases the probability of surviving freezing, a capacity which is enhanced in larger life-stages; adults and J4 stage juveniles show 50% survival at a supercooling point of -8.65° C. Laboratory incubations of field-fresh worms suggest that recent feeding is responsible for the movement between low and high groups. The cold-hardiness data for C. gerlachei provide interesting comparisons to the available data for microarthropods and create a precedent for seasonal changes between strategies of freezing tolerance and freezing intolerance in a field invertebrate population.     

Effect of Storage Environment on Hatching of the Cyst Nematode Globodera ellingtonae

Globodera spp. eggs go through a diapause, which remains dormant until favorable hatching conditions are reached. Because of the regulatory concerns with cyst nematodes, it is often only possible to rear eggs for research in the greenhouse. However, hatch is often lower for greenhouse-produced eggs than for eggs obtained from the field. The goal of this research was to determine storage conditions for Globodera ellingtonae eggs produced in the greenhouse that would increase percentage hatch. Over 3 yr, G. ellingtonae greenhouse-produced eggs were stored in different environments (−20°C, 4°C, room temperature, and the field) in either dry or moist soil. Percentage hatch after exposure to the different environments was determined in potato root diffusate. Across two experiments, field-produced eggs had higher hatch rates (65.2%) than greenhouse-produced eggs (10.4%). Temperature did not have an appreciable influence on hatch of eggs stored dry in two experiments (2.8% to 8.4% and 3.8% to 8.6%), but hatch of eggs stored in moist soil was significantly higher than in dry soil at all temperatures except −20°C (26.8% and 28.7%). However, the ability of G. ellingtonae greenhouse-, microplot-, and field-produced eggs to reproduce on potato in field microplots was not different. Although it may not be possible to produce G. ellingtonae eggs in the greenhouse that have the magnitude of hatch as those produced in the field, hatching can be greatly increased by storing eggs in moist soil at either 4°C or room temperature.     

Relationships between oviposition date, hatch date, and offspring size in the grasshopper Chorthippus brunneus

Abstract 1. The grasshopper Chorthippus brunneus has been shown to increase egg size with maternal age under constant laboratory conditions, such that late-laid eggs are larger than early laid eggs. In this study, an increase in the size of eggs (and hatchlings from those eggs) was recorded with date of oviposition in a field cage population. This suggests that the relationship between maternal age and egg size, observed previously in the laboratory, also occurs in the field. There was, however, some evidence that the behaviour of the maternal females in field cages was modified by the onset of autumnal weather at the end of the breeding season. Only a small number of eggs was laid in the last 3 weeks of the summer but these yielded relatively small hatchlings.
2. The date on which eggs were laid was correlated positively with their date of hatch in the following year. A consequence of this relationship, and that between oviposition date and egg size, was that size at hatch increased with date of hatch through most of the spring but then declined as the last few eggs hatched. Temporal variation in size at hatch parallelled temporal variation in the maternal females' investment in egg size in the previous year.
3. An undisturbed field population was monitored to assess whether the temporal variation in size at hatch resulted in size variation at eclosion in subsequent developmental stages. There were negative correlations between size at eclosion and date of eclosion at the third and fourth instars, suggesting that despite their smaller size at hatch, early hatchers experienced more favourable conditions for juvenile growth than late hatchers. The larger size at hatch of late hatchers may enhance their survival and compensate (albeit incompletely) for their reduced opportunity for growth. Female reproductive behaviour may represent an adaptive response to a predictable seasonal decline in offspring fitness at hatch.     

Neural function in an alpine grylloblattid: a comparison with the house cricket, Acheta domesticus

ABSTRACT. The effect of temperature on evoked activity in giant interneurons was compared in Grylloblatta sp. (an alpine insect with a temperature preference close to 0°C) and Acheta domesticus. The response to sound and air-puff stimulation of the abdominal cerci was monitored with extracellular electrodes placed under the ventral nerve cord. Responses to air puffs were elicited in Grylloblatta while the animal was supercooled to -6°C. The supercooling point was reached and freezing occurred in the range -5.5 to 8.5°C. The upper extinction temperature could not be determined due to massive spontaneous giant fibre activity in the 12–15°C range masking responses to air puffs. Lethal heat coma occurred at 15–20°C, although most animals did not recover from the spontaneous CNS activity which preceded it. The extinction ranges for Acheta giant neurons were 3.5-4.0°C and 42–44°C. Spike number peaked at 33–36 C and amplitude levels diminished as heat or cold coma was approached; -7.5 C was the mean supercooling point. Both species recovered from cold coma if supercooling was avoided; in Acheta , heat coma was also reversible. Giant fibre latencies in Acheta displayed a Q₁₀ of 1.2 above 11–14°C, below which a break occurred in the curve and delays increased sharply. Latencies for the grylloblattid exhibited a Q₁₀ of 2 but no break in the curve was observed until 0° C was approached. Spike number and amplitude increased with temperature until spontaneous CNS activity obliterated responses to air puffs. The potential role of unsaturated fatty acids in low temperature adaptation in Grylloblatta is discussed.     

Methods for the activation of the resting eggs of Daphnia

SUMMARY. 1. The conditions required to initiate development of resting eggs of thirty-six clones of Daphnia representing seven species were investigated.
2. The temperature of both dark incubation and subsequent light treatment are shown to affect hatch success. By varying these parameters the majority of resting eggs from each test clone were stimulated to develop. Arctic clones required a low hatching temperature (7°C), whereas clones from warmer climates hatched best at 14–21°C.
3. Variation in hatching cues existed between conspecific individuals from different collection sites. These differences suggest that research determining macro- and microgeographic patterns in hatching phenology would be fruitful.     

Photoperiod and temperature interaction in the determination of reproduction of the edible snail, Helix pomatia

Snails were kept in self-cleaning housing chambers in an artificially controlled environment. Mating was frequent under long days (18 h light) and rare under short days (8 h light) regardless of whether the snails were kept at 15 degrees C or 20 degrees C. An interaction between photoperiod and temperature was observed for egg laying. The number of eggs laid (45-50/snail) and the frequency of egg laying (90-130%) were greater in long than in short days (16-35/snail and 27-77%) but a temperature of 20 degrees C redressed, to some extent, the inhibitory effect of short days. At both temperatures only long photoperiods brought about cyclic reproduction over a period of 16 weeks, confirming the synchronizing role of photoperiod on the neuroendocrine control of egg laying in this species of snail.     

Effects of temperature on the development and survival of an endangered butterfly, Shijimiaeoides divinus barine (Leech) (Lepidoptera: Lycaenidae)

The effects of temperature on the development and survival of Shijimiaeoides divinus barine were examined in the laboratory in 2008. The eggs and larvae were reared at temperatures of 15, 17.5, 20, 25, 30 and 35°C with a long-day photoperiod of 16 h light : 8 h dark (16L : 8D). The highest hatchability of eggs was 88.0% at 20°C, but hatchability at high temperatures of 30 and 35°C was 30 and 0%, respectively. The lowest and highest survival rates from the first to third instar were 18.8% at 15°C and 76.9% at 20°C. Few deaths were observed after the fourth instar. The shortest developmental periods of the eggs and larvae were 4.0 and 15.8 days at 30°C, and the durations of the egg and larval stages increased significantly as the temperature decreased. The developmental zero and thermal constants were 9.6°C and 82.6 degree–days for the egg stage, and 10.7°C and 306.8 degree–days for the larval stage. The developmental period of the natural population of S. divinus barine in Azumino City, Nagano Prefecture was calculated using the developmental zero, thermal constants and Azumino City temperature data.