Repeated cycles of chilling and warming effectively terminate prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

Curculio sikkimensis (Coleoptera: Curculionidae) requires one or more years to complete its life cycle, owing to prolonged larval diapause. To compare the effects of temperature cycles and total periods of chilling on the termination of prolonged diapause, larvae were subjected to different chilling (5 degrees C) and warming (20 degrees C) cycles ranging from 30 to 720 days, and all cycles were repeated until the sum of chilling and warming periods reached 720 days. The prolonged diapause of C. sikkimensis was more effectively terminated by repeated cycles of chilling and warming than by prolonging the continuous chilling period. However, extremely short temperature cycles were not highly effective in enhancing diapause termination, even when such cycles were repeated many times. To examine the role of warming periods on diapause termination, diapause larvae were subjected to a sequence of chilling (120 days at 5 degrees C) and warming (240 days at 20 degrees C) with a warming period (0-120 days at 20 degrees C) inserted in the chilling period. Diapause larvae that were not reactivated in the first chilling period required exposure to a certain period of warming before they were able to complete diapause development in the subsequent chilling. Thus, C. sikkimensis appears to spread its reactivation times over several years in response to seasonal temperature cycles.     

Induction and development of winter larval diapause in a drosophilid fly,Chymomyza costata

Photoperiodic response during induction of larval hibernal diapause of Chymomyza costata was characterized and the course of diapause development was analyzed in the laboratory. C. costata becomes sensitive to photoperiodic stimuli during an unspecified stage of its early development (embryo, 1st larval instar); the sensitivity gradually increases during the 2nd and early 3rd larval instars and reaches its maximum just before the moment when it abruptly ceases at the age of 15-19 days after oviposition. Diapause intensifies during a period of 2-3 weeks after induction and, later, is maintained without apparent development until death (between 150 and 250 days) under 18 degrees C and a short-day photoperiod (L10:D14, SD). Diapause may be terminated in a horotelic process by exposure to a low temperature (2 degrees C) during which larvae subsequently (1) synchronize their post-diapause development (requires up to 14 days of chilling), (2) lose photoperiodic sensitivity (2 months), and finally (3) terminate diapause (5 months). Alternatively, diapause may be terminated in a tachytelic process by exposure to a high temperature (18 degrees C) and long-day photoperiod (L16:D8, LD) during which no synchronization occurs and pupariation takes place after a mean of 25.2 days (with a broad range from 8 to more than 50 days). Larvae that are transferred from LD to SD during their sensitive period switch their developmental programming from pupariation to diapause. Proliferation of adult primordial structures (imaginal discs, neuroblasts) slows down within 1 day after transfer. In contrast, whole body growth continues for at least 3 days before its rate slows down and matches the rate characteristic for SD conditions.     

Control of diapause in codling moth larvae

Diapause in a New Zealand strain of codling moth (Cydia pomonella Linnaeus [Lepidoptera: Olethreutidae]) was induced in larvae by photoperiods of 15 h or less. Once diapause had been initiated, it could not be terminated by any combination of conditions tested for at least 20 days after cocooning. In diapausing larvae a low rate of pupation occurred at 25 °C under a long day (18 h) photoperiod. A high rate of pupation was achieved under a long day regime when larvae were decocooned, and provided with apple as nourishment. Diapause could be terminated predictably in 94–100% of larvae by 1) conditioning at 15 °C and constant darkness for periods of 40–100 days, then 2) chilling at 2±2 °C and constant darkness for 20–50 days followed by 3) any post-chill condition periods at 25 °C, 18 h photoperiod. Complete diapause termination was achieved when 100 days conditioning was followed by 30 days or 50 days post-chill period. Under these conditions, 76% termination occurred in the post-chill period after 10 days, and 93% after 25 days.To terminate diapause in codling moth larvae, we recommend that a 100 days conditioning followed by 30 days chilling and 50 days post chilling periods be used.     

Effect of temperature on the termination of prolonged larval diapause in the chestnut weevil Curculio sikkimensis (Coleoptera: Curculionidae)

Adults of the chestnut weevil Curculio sikkimensis emerged over a 3-year period under laboratory and quasi-field conditions due to a prolonged diapause that occurred at the mature larval stage. Variable proportions of the larvae remained in diapause after a single cold (5 degrees C) treatment of 120 days. Extension of the chilling period to as long as 540 days did not increase the percentage of diapause termination, and excessively long chilling actually reduced the percentage. Chilling was not indispensable to the termination of larval diapause. Diapause intensity was very high and variable, and more than 1000 days at 20 degrees C was necessary to reactivate all diapause larvae. When the diapause larvae were exposed to cycles of low (5 degrees C for 120 days) and high (20 degrees C for 240 days) temperatures, the percentage of diapause termination reached 100% after two or three such cycles. Thus, the prolonged diapause of C. sikkimensis has characteristics similar to the common short winter diapause in other insects, but has unique characteristics that ensure polymodal reactivation over several years.     

Effects of temperature during chilling and pre-chilling periods on diapause and post-diapause development in a katydid, Eobiana engelhardti subtropica

In Eobiana engelhardti subtropica, early laid eggs reach the diapause stage in early autumn. For long periods before winter, the eggs are exposed to temperatures higher than their theoretical lower threshold for development. In contrast, late-laid eggs cannot reach their diapause stage before winter. Our study showed that E. e. subtropica copes with these difficulties via the thermal response involving embryonic diapause. In this katydid, the almost fully developed embryo undergoes an obligatory diapause. When diapause eggs were maintained at a temperature of 20 degrees C or higher, diapause persisted for a long time. Diapause was effectively terminated by temperatures ranging from 1 to 11 degrees C, and hatching occurred successfully at temperatures from 11 to 15 degrees C. In addition to the chilling temperature, pre-chilling temperature modified diapause intensity and hatching time. Diapause eggs hatched earlier after chilling when the pre-chilling temperature was lower, within a range of 14.5-25 degrees C. Thus, the low-temperature requirement for diapause termination prevents early laid eggs from untimely hatching in autumn, and low temperatures before and during winter decrease diapause intensity and shorten the hatching time in the following spring. When eggs were chilled before diapause, they tolerated chilling and averted diapause. Thus, even if eggs encounter low temperatures before diapause, they can hatch in the following spring.     

Diapause avoidance induced by low temperature in the yellow-spotted longicorn beetle, Psacothea hilaris

The diapause-averting effect of low temperature on pre-diapause larvae was examined in the yellow-spotted longicorn beetle, Psacothea hilaris. Larvae that had been reared under diapause-inducing conditions (25 °C , L12:D12) were temporarily exposed to 10 °C for various periods, and returned to the initial condition. Diapause was not averted by chilling for 15 days irrespective of the age of the larvae at chilling. After a 30-day chilling treatment, all of the 40- and 60-day-old larvae averted diapause, while diapause was averted in only one-third of the 10- and 20-day-old larvae. None of the pre-diapause larvae chilled for 60 days entered diapause irrespective of the age at chilling. With diapause avoidance, larvae that overwintered in earlier instars can start growing in earliest spring without any arrest; this phenomenon probably subserves the synchronization of larval development in a population.     

Thermal response and reversibility of prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

Curculio sikkimensis undergoes prolonged larval diapause that is terminated by chilling and warming cycles. To examine the effects of warming temperatures and their duration on diapause termination, we exposed diapause larvae that had not been reactivated after chilling at 5 °C to 20 or 25 °C and chilled them again before incubation at 20 °C. With increasing warming duration at 20 °C, diapause termination after chilling increased and shorter chilling durations became effective. In contrast, few or no larvae warmed at 25 °C terminated diapause after chilling, irrespective of the warming duration. To investigate the effect of warming temperature on diapause intensity, larvae with diapause weakened by initial incubation at 20 °C after the first chilling were subsequently incubated at 15, 20, or 25 °C, then chilled at 5 °C before incubation at 20 °C. Diapause termination increased significantly after the larvae were treated at 15 or 20 °C but decreased significantly after they were treated at 25 °C. The intensification of prolonged diapause at 25 °C was reversed when the larvae were transferred to 20 °C. Diapause intensity in C. sikkimensis therefore decreases at 20 °C, increases at 25 °C, and can be reversed by alternately exposing diapause larvae to 20 and 25 °C. In C. sikkimensis, prolonged diapause does not always proceed in one direction, and its intensity fluctuates in response to ambient temperature conditions.     

Cold-Hardiness and Supercooling Capacity in Diapausing and Nondiapausing Stages of the Cabbage Root Fly Delia radicum

Supercooling point (SCP) values and cold-hardiness were measured in individual ontogenetic stages of Delia radicum (Diptera:Anthomyiidae) in various physiological states (winter diapause, summer quiescence, and normal development). Winter diapause-destined mature third-instar larvae had a lower SCP (-9.9 degrees C) than their nondiapause counterparts (-5.2 degrees C), and more of them survived exposure to -10 degrees C for 5 h to pupariation and adult emergence. Values of SCPs were equal in both diapause and nondiapause states of prepupal and pupal stages. The lowest SCP (ca. -20 degrees C) was found in the stage of phanerocephalic pupa (PCP) regardless of the physiological state. The cold-hardiness of PCP corresponded with a low SCP value only in diapausing pupae stored for 80 days at 3 degrees C and in pupae which had terminated their diapause and whose further development was inhibited by storage at low temperatures (3 degrees C). Such pupae survived exposure to temperatures close to their SCP (14 days at -17 degrees C). However, this high cold-hardiness was only acquired after some time and/or exposure to 3 degrees C, as the PCP at the beginning of diapause showed significantly impaired cold-hardiness despite the fact that their SCP was low. The cold-hardiness of nondiapausing PCP did not correspond at all to that of low SCP, as no pupa survived the exposure to -17 degrees C for 1 day; survival rates at temperatures of -13.5 and -10 degrees C were also remarkably lower than those in diapausing pupae. Cold-hardiness in D. radicum was closely connected with the diapause syndrome but the changes in SCP value corresponded rather with the ontogeny of this insect. Copyright 1993, 1999 Academic Press.     

Biphasic effect of low temperature on completion of winter diapause in the onion maggot,Delia antiqua

The effect of low temperature on completion of winter diapause was investigated in the onion maggot, Delia antiqua (Diptera: Anthomyiidae). Diapause was completed under constant diapause-inducing conditions of 15 degrees C and 12L-12D, without any exposure to lower temperature. The pupal period for 50% adult emergence was 117 days. None of the cold treatments at 5.6 degrees C examined in the present study advanced adult emergence; on the contrary, they delayed it. Detailed analyses of the results revealed that diapause development in D. antiqua comprises two phases which differ in sensitivity to low temperature, with the phase shift occurring at around day 60 at 15 degrees C and 12L-12D. In the first phase of diapause development, low temperature (5.6 degrees C) had no effect on diapause development. In the latter phase, by contrast, diapause development was retarded in proportion to the duration of cold treatment.     

松毛虫赤眼蜂滞育诱导及解除条件研究

【目的】以柞蚕Antheraea pernyi卵为繁殖寄主,对松毛虫赤眼蜂Trichogramma dendrolim滞育诱导及解除条件进行研究,以解决赤眼蜂工厂化生产和大面积应用中面临的的中、长期储存问题。【方法】通过观测不同发育阶段(寄生柞蚕卵在26℃培养40、96和144 h)、滞育诱导温度(10、13和16℃)和诱导时间对松毛虫赤眼蜂滞育的影响,确定松毛虫赤眼蜂滞育诱导条件;通过观测滞育诱导温度和滞育后的贮藏温度对滞育解除的影响,确定松毛虫赤眼蜂滞育解除条件。【结果】在松毛虫赤眼蜂的不同发育阶段对其进行持续的低温刺激均能使其导入滞育,但以小幼阶段(26℃培养40 h)开始效果最佳,寄生卵在26℃培养40 h后,转入10℃和13℃下连续诱导31 d,滞育率可达100%和99.12%。滞育诱导温度和滞育后的贮藏温度对松毛虫赤眼蜂解除滞育所需时间和解除滞育后的羽化出蜂率有较大影响,10℃诱导滞育后置于1℃冷藏的赤眼蜂解除滞育所需时间最短,解除滞育后的羽化出蜂率和单卵出蜂数更高,更耐储存。此条件下冷藏约30 d开始打破滞育,在正常发育下温度下羽化出蜂,60 d羽化出蜂率达到95.24%,冷藏4个月后羽化出蜂率仍在60%以上,单卵出蜂数高于50头。【结论】松毛虫赤眼蜂最佳滞育诱导条件为26℃培养40 h后,转入10℃连续低温诱导31 d;最佳滞育解除条件为1℃低温储存,但储存期不能超过4个月。     

Diapause development in the chestnut weevilCurculio elephas

Larval diapause development in the chestnut weevilCurculio elephas (Coleoptera, Curculionidae) was studied in the laboratory at different temperatures. The results proved that exposure to low temperatures (3–6°C) in the period December–February is not required to complete diapause. The diapause is terminated in December and from January on, the larvae can initiate post-diapause morphogenesis in the laboratory, if temperatures allow it. In the field developmental rates are negligible during winter cold (4–6°C) and only after March morphogenesis can proceed with no interruption until adult emergence. Diapause and post-diapause quiescence contribute to individual synchronization for initiation of development. The observed spread of adult emergence was 30 days in the laboratory. This variability produced during post-diapause development may be a response to annual variation in the phenology of the chestnuts.     

Factors influencing the duration and termination of diapause in the Warehouse moth, Ephestia elutella

The influence of environmental factors on the duration of diapause was evaluated in larvae of Ephestia elutella (Hübner) reared in short photo-periods at 25C or below. Termination of diapause was hastened by long photoperiods, high temperatures, long periods at low temperature, or exposure to fumigants. Diapause terminated rapidly under long photoperiods at 30 or 25C, but not at 20C. The critical photoperiod for the termination of diapause was similar to that for induction, lying between 13 and 16 h at 25C. The longest duration of diapause occurred in constant darkness (DD) at 20C. However, batches of larvae reared at 20C in DD pupated a little sooner than batches reared under LD, if both were transferred at the start of diapause to warm, long-day conditions. Long exposure to low temperature reduced the number of long photoperiods necessary for the rapid termination of diapause at high temperature. Samples of larvae brought to the laboratory at monthly intervals from an unheated outbuilding in which they were overwintering, required an average of c. 200 days to pupate in DD at 25C when transferred in December, compared with only 32 days when transferred in February or March. By comparison, batches transferred to LD 16:8 at 25C required 39 days when transferred in December and 20–24 days in February and March. Holding at low temperature for long periods also encouraged synchronous emergence of the sexes. Duration of diapause was generally shorter in a laboratory stock than in a stock collected from the field.     

Effects of larval food shortage on diapause induction and adult traits in Taiwanese Monochamus alternatus alternatus

To confirm the facultative diapause of Monochamus alternatus alternatus Hope (Coleoptera: Cerambycidae) and to determine the relationships between available larval food resources, diapause, and adult traits, newly hatched larvae were inoculated singly on 98 Pinus densiflora Siebold & Zuccarini (Pinaceae) bolts and reared at 25 °C, 100% r.h., and L16:D8. Fifty adults emerged from them, between 70 and 126 days after larval inoculation. The remaining 48 bolts that did not produce adults were divided into two groups. One group was transferred to 10 °C, 100% r.h., and L8:D16, and returned 140–154 days later to the original conditions, resulting in adult emergence. The other group was maintained under the original conditions for a mean of 358 days. These bolts did not produce adults. Dissection revealed that development was arrested at final instar in pine bolts. The larvae developed into adults after being exposed to 10 °C, 100% r.h., and L8:D16 for 146 days. Consequently, this species has facultative diapause. Diapause incidence was estimated to be 0.42. Non‐linear model and one‐way ANOVA showed a positive correlation between adult body size and available food resources under conditions of food shortage, and no effects of diapause or available food resources on the ovariole number, respectively. When larvae were inoculated on 28 pine branch sections, the results were similar to those obtained from pine bolts and led to estimation of a low diapause incidence of 0.045. The combined data showed the inhibitory effect of food shortage on diapause induction. Diapause of M. a. alternatus, especially reduced diapause induction in response to environmental deterioration (food shortage), is discussed in relation to risk‐spreading.     

Effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle (Psacothea hilaris)

Abstract. .The effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae), were examined using a population from Ino, Japan. Diapausing insects obtained by rearing larvae under short daylength (12 or 13 h) at 25^oC were subjected to various treatments. When the photoperiod was changed at the same temperature, diapausing larvae showed a long-day response with a critical daylength between 13.5 and 14h. The diapause was terminated and consequently pupation occurred if the daylength was longer than 13.5 h. Chilling the diapausing larvae at 10^oC for 30 or more days also terminated diapause in most larvae irrespective of the photoperiods during and after chilling treatment. In contrast, the post-chilling photoperiod had a critical effect on development of diapausing larvae chilled for only 15 days.     

Effect of anoxia on diapause termination in eggs of the false melon beetle, Atrachya menetriesi

The effect of anoxia on diapause development in the leaf beetle Atrachya menetriesi was investigated to elucidate the role of oxygen in regulation of egg diapause. While anoxia alone had no effect on diapause termination, it decreased diapause intensity before chilling. Such an effect reached a maximum level when anoxia lasted for about 10 days. Anoxia applied during the pre-diapause stage also reduced diapause intensity. On the other hand, anoxia terminated diapause when the diapause intensity had been lowered by sufficient duration of chilling (50 days at 7.5 degrees C). The effect of anoxia was temperature dependent; the larger effect was elicited when anoxia was combined with a higher temperature. A 50-day chilling caused more than 20% of eggs to terminate diapause upon transfer to warm conditions. However, when this chilling period was interrupted on the 20th day by a 5-day exposure to a high temperature of 20, 25 or 30 degrees C, the effect of the former chilling was cancelled partially or completely, suggesting that warming reversed diapause development. This reversing effect of a high temperature, however, was not manifested when the warming was combined with anoxia. The results suggest that anoxia inhibits diapause reversal and facilitates a certain process of diapause development. The sequence of exposure to anoxia and chilling is not important.     

Life history traits of Pseudasphondylia rokuharensis (Diptera: Cecidomyiidae) affecting emergence of adults and synchronization with host plant phenology

To identify adaptive strategies of gall-inducing cecidomyiids, we studied the life history traits of Pseudasphondylia rokuharensis (Diptera: Cecidomyiidae), a univoltine species inducing fruit galls on a deciduous shrub, Viburnum dilatatum. Although univoltine gall midges that are associated with trees or shrubs are usually difficult to rear from immature stages under artificial conditions, we successfully reared P. rokuharensis from first instar to adult. Mature larvae entered diapause in autumn, and the diapause terminated after low temperature treatment (4 mo of incubation at 5 degrees C). The adults emerged within a shorter period of time than those without low temperature treatment. Thus, the diapause provides better synchronization of adult emergence in the spring. Because adults live for only a few days, this synchronization improves the chances of adults finding a mate. This is the first report on the mechanism of larval diapause termination for univoltine and tree- or shrub-associated gall midges. The numbers of days needed for adults to emerge under laboratory conditions after low temperature incubation were significantly different between two different localities. This result might suggest the possible existence of ecoclines in their life history parameters.     

Effects of temperature and photoperiod on the termination of larval diapause in Lucilia sericata (Diptera: Calliphoridae)

Larvae of the blow fly, Lucilia sericata (Meigen), enter diapause in the third instar after cessation of feeding. The effects of temperature and photoperiod on the termination of diapause were examined. The diapause terminated spontaneously under the diapause-inducing condition of 20 degrees C and LD 12:12, although pupariation was not synchronous. Diapause development proceeded under a low temperature of 7.5 degrees C. Transfer to long-day conditions of LD 16:8 or to a high temperature of 25 degrees C induced prompt and synchronous pupariation. Low temperatures in winter probably play a predominant role in the termination of diapause under natural conditions.     

Observations on the intensity of diapause and cold tolerance in larvae from twelve populations and two reciprocal crosses of the Indian meal moth, Plodia interpunctella

ABSTRACT. The duration of diapause in larvae of Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae) was assessed at 20°C in LD 11:13. Mean times from hatch to pupation for diapausing larvae from different populations ranged from 88 to 236 days. Most non-diapausing larvae pupated within 70 days at this temperature. Transferring diapausing larvae to 25°C and LD 9:15, or to 20°C and LD 15:9, 70 days after hatch reduced the subsequent mean time to pupation by 18–82% and 9–63% respectively. Only two population samples terminated diapause faster under LD 15:9 at 20°C than under LD 9:15 at 25°C. The mortality of diapausing larvae caused by 6- or 10-week exposures at 5, 7.5 or 10°C was generally less than 25%. Hybrids produced from a reciprocal cross between a temperate and a tropical African stock survived well. For other stocks there was some correlation between survival and diapause intensity. The low temperature regime which resulted in the greatest shortening of pupation time after return to the conditions used to induce diapause, did not always coincide with the temperature permitting the best survival. Results, however, indicate that some individuals of all stocks but one from the tropics are likely to survive in the U.K.     

Diapause Induction and Termination in Hyphantria cunea (Drury) (Lepidoptera: Arctiinae)

The fall webworm, Hyphantria cunea (Drury), enters facultative diapause as a pupa in response to short-day conditions during autumn. Photoperiodic response curves showed that the critical day length for diapause induction was 14 h 30 min, 14 h 25 min and 13 h 30 min at 22, 25 and 28°C, respectively. The photoperiodic responses under non-24 h light–dark cycles demonstrated that night length played an essential role in the determination of diapause. Experiments using a short day length interrupted by a 1-h light pulse exhibited two troughs of diapause inhibition and the effect of diapause inhibition was greater in the early scotophase than in the late scotophase. The diapause-inducing short day lengths of 8, 10 and 12 h evoked greater intensities of diapause than did 13 and 14 h. Diapause can be terminated without exposure to chilling, but chilling at 5°C for 90 and 120 d significantly accelerated diapause development, reduced mortality, and synchronized adult emergence. Additionally, the potential for H. cunea from the temperate region (Qingdao) to emerge and overwinter under field conditions in subtropical regions (Nanchang) of China was evaluated. Pupae that were transferred to Nanchang in early July showed a 60% survival rate and extremely dispersed pupal period (from 12 to 82 days), suggesting that some pupae may undergo summer diapause. Diapausing temperate region pupae that were moved out-of-doors in Nanchang during October showed approximately 20% overwintering survival; moreover, those pupae that overwintered successfully emerged the next spring during a period when their host plants would be available. The results indicate that this moth has the potential to expand its range into subtropical regions of China.     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).