Completion Of Diapause Research Articles

Lower Concentrations of the Glyphosate-Based Herbicide Roundup® Cause Developmental Defects in Artemia salina.

Roundup® is the most used glyphosate-based herbicide. During agricultural use it may directly contaminate existing aquatic ecosystems, posing severe concerns for the safety of nontarget terrestrial and aquatic organisms. We investigated the outcome of exposure to different concentrations of glyphosate in Roundup on cyst hatchability, toxicity, and teratogenic effects in the aquatic crustacean Artemia salina that inhabits diverse types of salt waters and, as a filter feeder, carries a greater risk of being exposed to pollutants. We found that exposure to 144 and 288 μg/ml glyphosate in Roundup resulted in cysts unable to complete diapause, and hatchability was completely inhibited during all exposure times tested (17-48 h). A glyphosate concentration of 288 μg/ml in Roundup was lethal to A. salina nauplii, and the lower concentrations (9, 18, 36, 72 μg/ml) had no significant effects on viability. In addition, sublethal and environmentally safe concentrations of glyphosate (0.72 μg/ml) in Roundup affected the early development of A. salina nauplii, with significantly decreased body lengths and reduced widths of the tail, abdomen, and head. The increased level of catalase activity observed in nauplii exposed to 0.72 μg/ml glyphosate for 24 h and those exposed to 7.2 and 72 μg/ml glyphosate for 48 h may be linked to excessive reactive oxygen species levels that had been induced by Roundup. In conclusion, Roundup containing >72 μg/ml glyphosate totally inhibited hatching of cysts and exerted toxic effects on A. salina nauplii. The increased prevalence of developmental defects in the nauplii observed at 0.72 μg/ml glyphosate signifies possible teratogenicity of Roundup exposure even at environmentally relevant concentrations of glyphosate, possibly due to disturbance of the antioxidant defenses, which needs further investigation. Environ Toxicol Chem 2023;00:1-9. © 2023 SETAC.

Phylogenomics revealed migration routes and adaptive radiation timing of Holarctic malaria mosquito species of the Maculipennis Group

BackgroundPhylogenetic analyses of closely related species of mosquitoes are important for better understanding the evolution of traits contributing to transmission of vector-borne diseases. Six out of 41 dominant malaria vectors of the genus Anopheles in the world belong to the Maculipennis Group, which is subdivided into two Nearctic subgroups (Freeborni and Quadrimaculatus) and one Palearctic (Maculipennis) subgroup. Although previous studies considered the Nearctic subgroups as ancestral, details about their relationship with the Palearctic subgroup, and their migration times and routes from North America to Eurasia remain controversial. The Palearctic species An. beklemishevi is currently included in the Nearctic Quadrimaculatus subgroup adding to the uncertainties in mosquito systematics.ResultsTo reconstruct historic relationships in the Maculipennis Group, we conducted a phylogenomic analysis of 11 Palearctic and 2 Nearctic species based on sequences of 1271 orthologous genes. The analysis indicated that the Palearctic species An. beklemishevi clusters together with other Eurasian species and represents a basal lineage among them. Also, An. beklemishevi is related more closely to An. freeborni, which inhabits the Western United States, rather than to An. quadrimaculatus, a species from the Eastern United States. The time-calibrated tree suggests a migration of mosquitoes in the Maculipennis Group from North America to Eurasia about 20–25 million years ago through the Bering Land Bridge. A Hybridcheck analysis demonstrated highly significant signatures of introgression events between allopatric species An. labranchiae and An. beklemishevi. The analysis also identified ancestral introgression events between An. sacharovi and its Nearctic relative An. freeborni despite their current geographic isolation. The reconstructed phylogeny suggests that vector competence and the ability to enter complete diapause during winter evolved independently in different lineages of the Maculipennis Group.ConclusionsOur phylogenomic analyses reveal migration routes and adaptive radiation timing of Holarctic malaria vectors and strongly support the inclusion of An. beklemishevi into the Maculipennis Subgroup. Detailed knowledge of the evolutionary history of the Maculipennis Subgroup provides a framework for examining the genomic changes related to ecological adaptation and susceptibility to human pathogens. These genomic variations may inform researchers about similar changes in the future providing insights into the patterns of disease transmission in Eurasia.

Gradually Increasing the Temperature Reduces the Diapause Termination Time of Trichogramma dendrolimi While Increasing Parasitoid Performance.

Simple SummaryTrichogramma dendrolimi is one of the most widely used biological control agents around the world, and diapause is a vital way to preserve Trichogramma products during mass production. However, diapause is a time-consuming process. In this study, we evaluated the effect of gradually increasing temperature on the diapause termination and the quality of Trichogramma products. The diapause termination rate reached the 95% required by practical applications when the induction period was high or in the treatments involving at least two-step variable temperatures (preceded by an induction period of 55, 60, and 70 days). Moreover, treatments consisting of at least two different temperatures led to higher parasitism and emergence rates while keeping the other parameters constant. In addition, the treatment with the highest temperature variation preceded by only 55 days of induction period had the highest population trend index. Our results demonstrate that gradually increasing temperature allows T. dendrolimi to complete diapause earlier than at present while increasing its potential pest control capacity and providing additional flexibility in mass production of T. dendrolimi.Trichogramma dendrolimi Matsumura is widely used as a biological control agent of many lepidopteran pests. Diapause has been used as an effective method to preserve the Trichogramma products during mass rearing production. However, it currently takes at least 70 days to break diapause, and we tested whether gradually increasing the temperature instead of using constant temperature could reduce the time of diapause termination and offer a higher flexibility to Trichogramma producers. The diapause termination rates of individuals kept at different conditions were measured, and five groups for which diapause termination rate reached the 95% were selected to test five biological parameters, including the number of eggs parasitized, the parasitism and emergence rates, the female sex ratio, the wing deformation rate, and the parasitoid longevity. Compared to the currently used procedure (70 days at 3 °C), treatments with at least two different temperatures resulted in higher parasitism and emergence rates while keeping the other parameters constant. The treatment that consisted of at least two different temperatures preceded by only 55 days of induction period had the highest population trend index, meaning that the population under these conditions grows more rapidly. Our results demonstrate that gradually increasing temperature allows T. dendrolimi to complete diapause earlier than at present while increasing its potential pest control capacity and providing additional flexibility in mass production of T. dendrolimi.

Diapause Termination in Invasive Populations of the Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) in Response to Photoperiod.

Understanding cues for diapause termination in insects can be valuable in predicting phenological events in their lifecycles. Once identified, such cues can be utilized as a biofix, the point at which the majority of individuals within a population begin to accumulate degree days. We investigated the impact of photoperiod on completion of reproductive diapause in the invasive eastern North American population of the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), by exposing diapausing females to varying light regimes in otherwise identical environments. The critical photoperiod estimated to initiate reproductive development in at least 50% of the potential reproductive population was 13.0-13.5 h, with increasing photoperiods coinciding with increased probability of females reproducing, earlier time to first oviposition, and higher rates of fecundity. These data on the species' response to photoperiod are in agreement with previous modeling that predicted the twin constraints of photoperiod and temperature on H. halys reproduction prevents populations that undergo diapause from producing more than two generations annually anywhere within the continental U.S. However, the facultative nature of diapause in H. halys leaves open the possibility that sub-populations may not enter diapause in some conditions, potentially allowing for additional annual generations.

Experimental Evidence Supporting an Obligate Adult Diapause for Spruce Beetle (Coleoptera: Curculionidae) from British Columbia.

Insects respond to environmental conditions with a variety of developmental responses which include changing developmental rates, or suppressing development altogether in quiescence or diapause. Such responses have important implications for survival and voltinism. The spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), has long been assumed to have an obligatory adult diapause based on field observations that adults always overwinter prior to dispersing and reproducing; however, it has never been experimentally demonstrated and recent evidence suggests that adults in some populations may exhibit facultative tendencies. We examined the emergence of adults at a constant 22°C after exposure to 2°C for 0 (no cold), 25, 50, and 75 d. Our observations of a delayed and extremely protracted emergence period in the absence of a substantive cold period, which could last several months, in combination with rapid, synchronous mass emergence after a substantive cold period, are most consistent with an obligate diapause. Approximately 50% of individuals could complete diapause in 55 d at 2°C, and 75 d of cold was adequate for almost all individuals to complete diapause. Beetles that emerged slowly over time may still have been in diapause; however, additional research would be required to test this hypothesis. Conditions throughout the beetle's range in Canada should facilitate successful completion of diapause. An obligate adult diapause for spruce beetle populations in western Canada would limit the shortest possible life cycle to 1 yr, but would also serve to maintain an adaptive 1-yr life cycle, especially under a changing climate.

Effects of photoperiod, temperature and aging on adult diapause termination and post-diapause development in female Asian comma butterflies, Polygonia c-aureum Linnaeus (Lepidoptera: Nymphalidae).

Polygonia c-aureum females exhibit photoperiodically induced imaginal diapause, characterized by cessation of ovarian development. Females grown at a short daylength (SD) entered imaginal diapause, whereas those grown at a long daylength (LD) produced eggs rapidly after adult emergence at 21°C. The termination of diapause was influenced by daylength: diapause ended faster at LD than SD. Complete termination of diapause took 30 days in unchilled females reared under LD at 21°C. On the other hand, prompt, synchronized and strong diapause termination occurred at post-chilling periods. Photoperiods at post-chilling periods affected ovarian development, when the length of pre-chilling periods or the length of chilling periods was shorter, suggesting that these treatments were not enough to complete diapause development. Ovarian development proceeded earlier in chilled and subsequent warmed females than unchilled females. Wing damage was remarkable at post-chilling periods when females were reared under an adequate length of pre-chilling and chilling periods, especially comparing with females under pre-overwintering conditions without chilling, indicating that post-diapause reproductive development was weak in unchilled females. Thus, exposure to low temperatures is necessary for a strong diapause termination in this butterfly.

The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), a vector of dengue, chikungunya and zika viruses, reaches Portugal (Diptera: Culicidae).

The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), is a tropical species originally from south-eastern Asia (Hawley, 1988). It has experienced a rampant human-mediated range expansion since the 1970s to now occupy almost the whole of the tropical and subtropical areas of the world. As an eclectic haematophagous species, it attacks humans and is able to use a number of man-made and natural structures where stagnant water is present (Estrada-Franco Craig, 1995). Eggs are able to survive for extended periods of time in complete dryness and diapause over unsuitable cold season, making it an especially resilient species (Hawley, 1988).

Impact of Prolonged Absence of Low Temperature on Adult Eclosion Patterns of Western Cherry Fruit Fly (Diptera: Tephritidae).

Western cherry fruit fly, Rhagoletis indifferens (Curran) (Diptera: Tephritidae), is a serious pest of cherries (Prunus spp.) in the Pacific Northwest of the United States. Previous research suggests that R. indifferens is unlikely to establish in commercial cherry production areas in California and in tropical export markets because cold temperatures, below 5 °C, in those regions appear insufficient to complete diapause. However, it is unclear how prolonged absence of cold exposure affects diapause termination in R. indifferens. Here, we examined this question by exposing R. indifferens pupae for 40 wk to simulated temperate and tropical conditions of 23 or 26 °C, 40 or 80% RH, and a photoperiod of 16:8 or 12:12 (L:D) h. Eclosion patterns among fly groups in the four conditions did not differ. For all groups, fly eclosion from pupae not exposed to cold exhibited a bimodal distribution. The first major peak, comprising 3.2% of the total fly emergence, occurred at 1-10 wk. The second major peak, comprising the remaining 96.8%, occurred at a mode of ∼30 wk. Based on responses to no cold and cold (3 ± 1.5 °C) exposures, there were three distinct pupal diapause groups: the first eclosion group was likely nondiapausing pupae; the second eclosion group was likely diapausing pupae; a third group that remained viable but did not produce adults after 40 wk may represent prolonged dormancy pupae. We suggest that eclosion of adults after prolonged absence of cold exposure needs to be incorporated into models for potential fly establishment in warm climates.

Emergence of the overwintering generation of peach fruit moth (Carposina sasakii) depends on diapause and spring soil temperatures

Survival rate and emergence timing of the overwintering generation of many temperate agricultural pests is expected to affect their population dynamics and damage potential. However the impact of fluctuating winter and spring conditions on the successful emergence of insects post-diapause is generally poorly known. Here we characterize diapause responses in the peach fruit moth (PFM) pest, Carposina sasakii Matsumura, which overwinters at the larval stage in soil. Temperatures at a depth of 5cm fluctuated markedly in early spring during the critical PFM post-diapause period (late December to mid-April). By removing outdoor larval samples over this period, we show that the completion of diapause for PFM in northern China starts from late January and continues until March. This extended developmental period is accompanied by an ongoing loss of cold resistance. Temperature conditions experienced in the field were associated with cold tolerance and emergence times, and reduced cold tolerance was associated with shorter emergence time. Cryoprotectants declined from late December, and levels were associated with changes in the supercooling point (SCP) of the larvae, but both correlated weakly to survival under cold stress during the post-diapause period. These findings suggest that diapause stage and soil temperatures should be taken into account when predicting field dynamics of soil-dwelling overwintering insects based on degree day accumulation models and other approaches.

Why is the number of days required for induction of adult diapause in the linden bug Pyrrhocoris apterus fewer in the larval than in the adult stage?

Adult females of Pyrrhocoris apterus, programmed for diapause by short-day (SD) photoperiod and those programmed for reproduction by long-day (LD) retain photoperiodic information in continuous darkness (DD) until death. However, if the interruption of SD by DD is made in the course of diapause programming in adults, then the incidence of diapause depends on the number of SD cycles received before DD, with no evidence that the photoperiodic clock is free-running at DD to complete diapause induction. These results indicate that the photoperiodic clock is stopped after transfer to DD and the information accumulated before transfer to DD is maintained. Diapause programming in the adult stage requires 9–10 SD cycles to induce diapause in 80% of individuals. However, if the diapause programming starts after ecdysis of LD-larvae to the last instar, only 3 SD cycles before transfer to DD are required for diapause in 80% of individuals. Surprisingly, if the newly ecdysed last instar LD-larvae, sensitive to photoperiod, are transferred to DD (thus they did not experience any SD), diapause occurs in 40% of the individuals. Thus, diapause ‘information’ is present in LD-larvae and is responsible for a lower number of SD required for diapause induction in the larval than in the adult stage.

Mosquito body clock regulates winter shut down

For some species, surviving winter is too much of an ordeal to keep everything ticking over. So, as soon as the days reach a certain length, adult Northern house mosquitoes (Culex pipiens) prepare for their seasonal reproductive winter shut down (diapause), ready to re-commence reproduction in the spring. ‘Much is known about the photoperiodic cues, endocrine signals and physiological changes that regulate and accompany diapause’, says Megan Meuti from The Ohio State University, USA. However, little was known about the mechanism that the insects use to measure day length or how they convert the information into the hormone signals that orchestrate the insects' diapause. Although many insects are known to regulate body functions using a light-regulated circadian clock, it was not clear whether this mechanism triggered preparation for diapause in C. pipiens, so Meuti and her colleagues, Mary Stone, Tomoko Ikeno and David Denlinger, began investing the effects of day length on key components of the mosquito's circadian clock (p. 412).The team explain that the expression levels of the five components of the molecular clock (Clock, cycle, period, timeless and cryptochrome2) rise and fall in relation to the length of daylight exposure over a 24 h period, so they decided to find out whether the clock continued running during diapause. Measuring expression of period, timeless, cycle and cryptochrome2 in the brains of adult female mosquitoes that had been exposed to daylight periods of different length to stimulate the onset and duration of diapause, the team discovered that the mRNA levels continued cycling – even when the insects were plunged into the depths of winter. Meuti explains that the clock has to function throughout the seasons to ensure that the insect knows when to emerge from diapause and says, ‘Our observations… support the circadian basis for diapause initiation and maintenance in C. pipiens and suggest that the rhythmic oscillations of these transcripts may be involved in continually measuring night length throughout diapause’. The team were a little perplexed when they discovered that expression of cryptochrome became reversed (peaking at night) after emergence from diapause; however, they suspect that this reflects that the insects are most active in the early morning.Having confirmed that the insect's circadian clock plays a role in regulating diapause, the team began investigating the individual role of each of the clock's components. Injecting an RNA molecule designed to lock up the mRNA and prevent transcription of one individual component of the clock into young female adult mosquitoes and then monitoring the effect of the component loss on their fatness and fertility, the team found that females that were experiencing short daylight exposures – which should have induced diapause – failed to enter the condition when period, timeless and cryptochrome mRNA levels were reduced. However, when the team inactivated another component of the molecular clock – pigment dispersing factor – under long daylight conditions, the loss triggered diapause in insects that should have been able to reproduce.‘Our results implicate the circadian clock in the initiation of diapause in C. pipiens’, says Meuti, who adds that she is keen to understand the complete diapause pathway, from the measurement of day length to the physiological mechanisms that allow the mosquitoes to survive the winter. Explaining that C. pipiens is a carrier of major diseases such as West Nile virus, St Louis encephalitis and filariasis, Meuti is hoping to use this knowledge against the insect to control disease transmission – by either averting diapause in winter or initiating diapause in other seasons.

Temperature during the free-living phase of an ectoparasite influences the emergence pattern of the infective phase

Understanding the population dynamics and co-evolution of host–parasite systems requires detailed knowledge of their phenology which, in turn, requires a deep knowledge of the effect of abiotic factors on the life cycles of organisms. Temperature is known to be a key environmental influence that participates in the regulation of diapause. Yet, not much is known about the effect of temperature on the free-living stages of true parasites and how it may influence host–parasite interactions. Here we experimentally study the effect of ambient temperature on overwintering pupae of Carnus hemapterus (Diptera, Carnidae), an ectoparasitic fly of various bird species. We also test whether chilling is a prerequisite for completion of diapause in this species. In the course of three winter seasons we experimentally exposed carnid pupae from nests of various host species to spring temperatures with and without chilling and recorded the emergence patterns in experimental and control groups. Experimental groups showed an advanced emergence date, a lower emergence rate and, consequently, a protracted emergence period. Chilling had no obvious effect on the start of emergence but it did advance the mean emergence date, shortened the length of the emergence period when compared with the control treatment and increased the emergence rate when compared with the spring treatment. This study identifies an environmental cue, namely temperature during the free-living stage, affecting the emergence of a widespread parasite and demonstrates the plasticity of diapause in this parasite. Our findings are of potential significance in understanding host–parasite interactions.

Optimal Low Temperature and Chilling Period for Both Summer and Winter Diapause Development in Pieris melete: Based on a Similar Mechanism

The cabbage butterfly, Pieris melete hibernates and aestivates as a diapausing pupa. We present evidence that the optimum of low temperature and optimal chilling periods for both summer and winter diapause development are based on a similar mechanism. Summer or winter diapausing pupae were exposed to different low temperatures of 1, 5, 10 or 15°C for different chilling periods (ranging from 30 to 120 d) or chilling treatments started at different stages of diapause, and were then transferred to 20°C, LD12.5∶11.5 to terminate diapause. Chilling temperature and duration had a significant effect on the development of aestivating and hibernating pupae. The durations of diapause for both aestivating and hibernating pupae were significantly shorter when they were exposed to low temperatures of 1, 5 or 10°C for 50 or 60 days, suggesting that the optimum chilling temperatures for diapause development were between 1 and 10°C and the required optimal chilling period was about 50–60 days. Eighty days of chilling was efficient for the completion of both summer and winter diapause. When chilling periods were ≥90 days, the durations of summer and winter diapause were significantly lengthened; however, the adult emergence was more synchronous. The adaptive significance of a similar mechanism on summer and winter diapause development is discussed.

Evidence for reversible change in intensity of prolonged diapause in the chestnut weevil Curculio sikkimensis

The chestnut weevil Curculio sikkimensis undergoes a prolonged larval diapause that is completed by repeated exposure to chilling and warming. We examined the possible reversibility of diapause intensity in response to temperature changes. All larvae were subjected to an initial chilling followed by incubation at 20°C to force pupation of the 1-year-type larvae that require only one winter for diapause completion. We then exposed the larvae remaining in prolonged diapause to a second chilling at 5°C for different lengths of time, preceded or not preceded by incubation at 20°C (moderately high) and/or 25°C (high) and followed by a final post-chilling reincubation at 20°C. Many of the prolonged-diapausing larvae subjected only to a brief second chilling were re-activated upon reincubation. However, short exposure to 25°C before this second chilling dramatically decreased the percentage of larvae completing diapause. When larvae were exposed to 25°C for a short period, then incubated at 20°C and subjected to the brief second chilling, many were re-activated during reincubation. The chilling time required for most of the larvae to complete diapause decreased after pre-chilling incubation at 20°C and increased after incubation at 25°C. These results demonstrate that diapause intensity in C. sikkimensis changes reversibly in response to changes in ambient temperature.

The long summer: Pre-wintering temperatures affect metabolic expenditure and winter survival in a solitary bee

The impact of climate change on insect populations depends on specific life cycle traits and physiological adaptations. The solitary bee Osmia lignaria winters as a pre-emergent adult, and requires a period of cold temperature for winter diapause completion. It is a univoltine species, and diapause induction does not depend on photoperiod. To understand the potential effects of longer summers on O. lignaria populations, we exposed individuals to three treatments simulating early, mid and late winter arrivals, and measured respiration rates, metabolic expenditure, weight loss, fat body depletion, lipid levels and winter mortality. The early-winter treatment disrupted diapause development, but had no apparent negative effects on fitness. In contrast, late-winter bees had a greater energetic expenditure (1.5-fold), weight (1.4-fold) and lipid (2-fold) loss, greater fat body depletion, and a 19% increase in mortality compared to mid-winter bees. We also monitored adult eclosion and arrival of winter temperatures under natural conditions in four years. We found a positive correlation between mean degree-day accumulation during pre-wintering (a measure of asynchrony between adult eclosion and winter arrival) and yearly winter mortality. Individually, bees experiencing greater degree-day accumulations exhibited reduced post-winter longevity. Timing of adult eclosion in O. lignaria is dependent on the duration of the prepupal period, which occurs in mid-summer, is also diapause-mediated, and is longer in populations from southerly latitudes. In a global warming scenario, we expect long summer diapause phenotypes to replace short summer diapause phenotypes, effectively maintaining short pre-wintering periods in spite of delayed winter arrivals.

The effect of temperature and light conditions on diapause induction in a Korean population of Neoseiulus womersleyi Schicha (Acari: Phytoseiidae)

To determine the condition for diapause induction of a Korean population of Neoseiulus womersleyi, combinations of constant temperatures (14, 16, 18, 20 and 25 °C) and photoperiods (0, 8, 10, 12, 14, 16 and 24 h photophase) were used from egg to adult emergence. Diapause induction was determined by reproductive cessation of adult females. Lower temperature and shorter photophase resulted in higher diapause induction. Critical photophases for diapause induction were 10 and 12 h at 18 and 16 °C, respectively. Diapause-induced N. womersleyi adult females consumed significantly fewer eggs of the two-spotted spider mite, Tetranychus urticae, than non-induced females. Field monitoring of N. womersleyi showed that there was no egg-bearing female after 282 Julian date, while a model estimated complete diapause induction at 288 Julian date. Diapause of this predatory mite occurred approximately 2 weeks before diapause of its main prey, T. urticae, in Korean apple orchards. Further study perspectives are discussed relative to the spider mite biological control system in fruit orchards.

The combined effect of photoperiod and temperature on egg dormancy in an island and a mainland population of the hemlock looper, Lambdina fiscellaria

AbstractEmbryonic dormancy characteristics of the hemlock looper (HL), Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae), an important coniferous defoliator, were investigated using eggs from an island (Newfoundland) and a mainland (Quebec) population in eastern Canada. We determined (1) the pre‐diapause duration or time required for eggs to change color at 15 °C, under L16:D8 and L12:D12, (2) the percent hatch and time to hatch of early‐diapausing eggs that were, as of 1 September, either (a) incubated under each combination of three photoperiods (L16:D8, L12:D12, or L8:D16) and three temperatures (15, 20, or 25 °C) or (b) stored outdoors prior to their monthly incubation (October–May) under the same treatments, and (3) the diapause duration at 15 °C. The two HL ecotypes completed their pre‐diapause phase in ca. 15 days under long‐day photoperiod. In the mainland ecotype, photoperiod did not influence the pre‐diapause duration. Regardless of photoperiod and ecotype, only eggs incubated continuously at 15 °C hatched successfully after ca. 120 days. Temperature was the most important factor modulating the dormancy of eggs acclimated outdoors, in both ecotypes. From October to December (diapause phase), percent egg hatch at 20 and 25 °C increased from low (20%) to levels similar to those obtained at 15 °C (70%). These percentages remained stable throughout the post‐diapause phase (January–May). Time to hatch, which was shorter at warmer temperatures, decreased from October to December at all temperatures. It remained stable from January to March (quiescence), however, and declined thereafter. Eggs from the island were heavier than those from the mainland and their odds of hatching were 2.3 times higher. At 15 °C, diapause lasted ca. 90 days. Our findings indicate that eggs from the two HL ecotypes (1) undergo an obligatory diapause, (2) complete diapause without pre‐exposure to cold, (3) respond similarly to photoperiod and temperature during diapause and post‐diapause, and (4) do not hatch successfully after prolonged exposure to high temperatures.

Effect of temperature regime on diapause intensity in an adult-wintering Hymenopteran with obligate diapause

Osmia lignaria is a solitary bee that over-winters as a fully eclosed, cocooned, unfed adult. Our objective is to understand the effect of wintering temperature on diapause maintenance and termination in this species. We measure respiration rates and weight loss in individuals exposed to various wintering temperatures (0, 4, 7, 22 degrees C, outdoors) and durations (28, 84, 140, 196, 252 days). We use time to emerge and respiration response (respiration rate measured at 22 degrees C) as indicators of diapause intensity. Adults spontaneously lower their respiration rates to approximately 0.1 ml/gh within 1 month after adult eclosion, indicating obligatory diapause. Non-wintered individuals maintain low respiration rates, but lose weight rapidly and die by mid-winter. In wintered adults, two phases can be distinguished. First, respiration response undergoes a rapid increase and then reaches a plateau. This phase is similar in bees wintered at 0, 4 and 7 degrees C. In the second phase, respiration response undergoes an exponential increase, which is more pronounced at the warmer temperatures. Composite exponential functions provide a good fit to the observed respiration patterns. Adults whose respiration response has reached 0.45 ml/gh emerge promptly when exposed to 20 degrees C, indicating diapause completion. Individuals wintered for short periods do not reach such respiration levels. When exposed to 20 degrees C these individuals lower their metabolic rate, and their emergence time is extended. The relationship between respiration rates and emergence time follows a negative exponential function. We propose two alternative models of diapause termination to interpret these results.

Reversible change in embryonic diapause intensity by mild temperature in the Chinese rice grasshopper, Oxya chinensis

AbstractThe effects of temperature on maintenance and termination of embryonic diapause were investigated in Jining (35.4°N, 116.6°E) and Sihong (33.5°N, 118.2°E) strains of the Chinese rice grasshopper, Oxya chinensis Thunberg (Orthoptera: Catantopidae). Eggs of both strains entered diapause when incubated at 30, 25, or 20 °C. Chilling at 8 °C had an evident effect on diapause termination and almost all eggs chilled for 60 days ended diapause development. Chilling of eggs at 8 °C for only 20 days failed to result in any hatching at 20 °C, suggesting that such level of chilling was not enough to induce diapause termination. However, the treatment combining incubation of eggs at 30 °C for varying lengths of time with subsequent incubation to 20 °C had a distinct effect on the completion of diapause of the eggs. The results indicate that there were two temperature optima, that is, low temperature (chilling) and high temperature, for diapause development in this grasshopper species. Incubation of chilled eggs at 20 °C for 5–15 days followed by further incubation at 25 °C reduced termination of diapause significantly compared with the eggs only chilled at 8 °C. Exposure of eggs chilled at 8 °C to a pulse of 25 °C from 1 to 7 days, separated by a 20‐day interval at 8 °C, resulted in a decrease in the percentage of successfully hatched eggs as the length of the pulse of 25 °C increased. The results suggest that diapause intensity may be restored at moderately high temperatures. This reversible change in diapause intensity would play an important role in maintaining diapause before winter.

Factors affecting the natural duration of diapause and post-diapause development in the Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae)

Sesamia nonagrioides responds to photoperiod for diapause termination at high temperature with a Type II response curve, and only photoperiods longer than 12:12 terminate diapause. However, these photoperiods never occur in the field when diapausing larvae are competent to terminate diapause. Under a temperature similar to the natural field temperatures diapause terminates spontaneously in approximately 4 months, which ensures that the larvae reach the middle of winter without pupation. S. nonagrioides larvae pupate after going through a specific number of light–dark cycles or days: the required day number (RDN) for diapause completion. This RDN could be modulated by temperature but more research is necessary to clarify this point. In post-diapause development, when a suitable temperature threshold is considered, the absolute accumulation of heat is more important than whether the temperature received is fluctuating or constant. The temperature threshold for diapause and post-diapause development was lower than the temperature threshold of larvae in continuous development. This is important for adjusting phenological models in S. nonagrioides and in other species, and may explain why in many cases adults appear in the field when the supposed temperature threshold for development has not been attained.