Asymmetric song responses in coexisting Japanese cicadas

Diel partitioning of singing, which has been observed from the tropics to the temperate regions, is among the various mechanisms of sound partitioning found in multispecies cicada assemblages and is regarded as an important mechanism of coexistence. Using playback experiments, we studied interspecific interference between two Japanese cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata, which exhibit similar peak frequencies in their calling songs and different diel patterns of song activity. We found that the males of the two species had different song response patterns: C. facialis responded significantly more to conspecific calling songs than G. nigrofuscata. These results suggest that male C. facialis have evolved more intense conspecific song recognition than G. nigrofuscata. This may cause male G. nigrofuscata to avoid destructive acoustic interference during their active singing time.     

An analysis of diapause and resistance in the egg stage of Floronia bucculenta (Araneida: Linyphiidae)

Summary Floronia bucculenta hibernates in the egg stage; the egg sacs are deposited on the leaves of grass tussocks without any shelter. The morphogenesis of the eggs was divided into 10 arbitrarily chosen stages, in order to test the dependence of embryonic development on temperature in the laboratory. The eggs developed slowly at 23°C, 16°, 12.5°; embryogenesis stopped after 70–45 days, when prosomal appendage rudiments began to form. At 10°, 7.5°, 5°, 0° complete embryogenesis was possible until the emergence of the first complete stage. The eggs developed most rapidly at 5° (mean developmental time 203 days). The egg development was normal at 5° and 0°, when compared with the timetable of the embryogenesis of the linyphiid Bathyphantes gracilis, a species which has no egg diapause. At 7.5° and 10° the embryogenesis was strongly delayed during the median phases of development (elongation of the germ band, formation of prosomal appendages); after reversion the development was accelerated (postdiapause phase). After long exposure to low temperatures (-10° to +10°) the diapause was terminated. A temperature of 0° was optimal (minimal time of exposure 8–9 weeks). The time required for embryonic development of postdiapause eggs decreased hyperbolically with increasing temperature. In the field the median phases of embryogenesis were retarded by low ambient temperatures; diapause was terminated from late December to mid-January. The spread of hatching in spring was 7–15 days.During the diapause phase the O₂-consumption of the eggs at 25° was depressed. It rose from 1.55 (in late diapause) to 4.21 ml/100 eggs·h at the onset of postdiapause, whereas O₂-utilization did not change significantly at 5° (from 0.54 to 0.61 ml/100 eggs·h just after the termination of diapause).The diapause phase was not characterized by higher resistance to cold, drought, or flooding. As compared with single eggs removed from the cocoon, the silken wall of the intact egg sac did not affect the survival of postdiapause eggs exposed to-15° (LD₅₀=28 days); it raised, however, the survival time of eggs exposed to a R.H. of 32% (at 5°) or flooding by distilled water (at 5°): from LD₅₀=37 to 68 days at drought, from LD₅₀=30 to 92 days at flooding.Diapause is important for synchronizing the life-cycle of F. bucculenta with the seasonal fluctuations of environment. The egg stage is highly tolerant to the extreme factors of the winter. Some implications of the relation of the studied spider to its habitat are discussed.     

Inheritance of the photoperiodic response controlling imaginal summer diapause in the cabbage beetle, Colaphellus bowringi

Adults of the cabbage beetle Colaphellus bowringi display a summer diapause in response to the exposure of their larvae to long photoperiods. In the present study, the inheritance of the photoperiodic response controlling summer diapause in C. bowringi by crossing a high diapause strain (D strain) with a laboratory selected nondiapause strain (N strain) was investigated under different photoperiods at 22, 25 and 28 °C. The beetles in both reciprocal crosses and backcrosses showed a clear short-day response for the induction of diapause at all temperatures, similar to that of the D strain, suggesting that photoperiodic response of this beetle is heritable. The diapause incidences in the progeny from all the crosses under LD 15:9 or LD 12:12 at 25 °C suggest that genetic and genetic-environmental interactions are involved in diapause induction. The incidence of diapauses in F₁ progeny was significantly lower than that in the D × D strain but significantly higher than that in the N × N strain, indicating that the diapause capability is inherited in an incomplete dominant manner. The incidence of diapause was greater among the offspring of hybrid females when those females had a D strain mother or grandmother rather than a N strain mother or grandmother, indicating that maternal effects on diapause induction are stronger than paternal effects. The laboratory selected nondiapause strain also showed a short-day photoperiodic response at a low temperature of 22 °C, indicating that the photoperiodic photoreceptor and photoperiodic clock still function in the nondiapause strain.     

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.     

Diapause pupal color diphenism induced by temperature and humidity conditions in Byasa alcinous (Lepidoptera: Papilionidae)

We investigated whether diapause pupae of Byasa alcinous exhibit pupal color diphenism (or polyphenism) similar to the diapause pupal color polyphenism shown by Papilio xuthus. All diapause pupae of B. alcinous observed in the field during winter showed pupal coloration of a dark-brown type. When larvae were reared and allowed to reach pupation under short-day conditions at 18 °C under a 60 ± 5% relative humidity, diapause pupae exhibited pupal color types of brown (33%), light-brown (25%), yellowish-brown (21%), diapause light-yellow (14%) and diapause yellow (7%). When mature larvae reared at 18 °C were transferred and allowed to reach pupation at 10 °C and 25 °C under a 60 ± 5% relative humidity after a gut purge, the developmental ratio of brown and light-brown, yellowish-brown, and diapause light-yellow and diapause yellow types was 91.2, 8.8 and 0.0% at 10 °C, and 12.2, 48.8 and 39.0% at 25 °C, respectively. On the other hand, when mature larvae reared at 18 °C were transferred and allowed to reach pupation at 10 °C, 18 °C and 25 °C under an over 90% relative humidity after a gut purge, the developmental ratio of brown and light-brown, yellowish-brown, and diapause light-yellow and diapause yellow types was 79.8, 16.9 and 3.3% at 10 °C, 14.5, 26.9 and 58.6% at 18 °C, and 8.3, 21.2 and 70.5% at 25 °C, respectively. These results indicate that diapause pupae of brown types are induced by lower temperature and humidity conditions, whereas yellow types are induced by higher temperature and humidity conditions. The findings of this study show that diapause pupae of B. alcinous exhibit pupal color diphenism comprising brown and diapause yellow types, and suggest that temperature and humidity experienced after a gut purge are the main factors that affect the diapause pupal coloration of B. alcinous as environmental cues.     

Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28 °C for 2 h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3 °C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT₅₀ of −19.7 and −13.3 °C, respectively. Further, we also examined the effects of cold acclimation (10 d at 0 or 5 °C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5 °C. Acclimation at 5 °C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT₅₀ of −22.0 and −17.1 °C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.     

Diapause termination, post-diapause development and reproduction in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

Effects of photoperiod and cold exposure on diapause termination, post-diapause development and reproduction in Loxostege sticticalis were examined. Larvae were reared at diapause inducing condition (22 °C, L:D 12:12) consistently or transferred to long day photoperiod (L:D 16:8) and darkness (L:D 0:24) respectively, after entering into diapause. Diapause was terminated in approximately 40% of the larvae after 36 days, and no significant differences were observed between photoperiods, suggesting larval diapause was terminated spontaneously without being induced by photoperiods. Cold exposure significantly hastened diapause termination. The diapause termination incidence increased significantly with peaks of 98% at both 5 °C and 0 °C exposure for 30 days, as compared to 42% in controls not exposed to cold, while the mortality and number of days required for diapause termination decreased dramatically. The optimal low temperature exposure periods under 5 °C or 0 °C were 20 days and 30 days, showing a higher termination incidence and shorter time for diapause termination. This suggests that the low temperatures in winter play an important role in diapause termination under natural conditions. The threshold temperatures for post-diapause development in prepupae and pupae were 9.13 °C and 10.60 °C respectively, with corresponding accumulations of 125 and 200 degree-days. Adults that experienced larval diapause significantly delayed their first oviposition, oviposition period was prolonged, and the lifetime number of eggs laid was decreased, however both males and females have significantly longer longevity. The field validation of diapause termination, the degree-days model, and the relationship between diapause and migration in L. sticticalis were also discussed.     

Preliminary studies on cryopreservation of snakehead (Channa striata) embryos

This paper reports the findings of the ongoing studies on cryopreservation of the snakehead, Channa striata embryos. The specific objective of this study was to collect data on the sensitivity of C. striata embryo hatching rate to low temperatures at two different developmental stages in the presence of four different cryoprotectants. Embryos at morula and heartbeat stages were selected and incubated in 1 M dimethyl sulfoxide (Me₂SO), 1 M ethylene glycol (EG), 1 M methanol (MeOH) and 0.1 M sucrose solutions at different temperatures for a period of time. Embryos were kept at 24 °C (control), 15 °C, 4 °C and −2 °C for 5 min, 1 h and 3 h. Following these treatments, the embryos were then transferred into a 24 °C water bath until hatch to evaluate the hatching rate. The results showed that there was a significant decrease of hatching rate in both developmental stages following exposure to 4 °C and −2 °C at 1 h and 3 h exposure in each treatment. Heartbeat stage was more tolerant against chilling at −2 °C for 3 h exposure in Me₂SO followed by MeOH, sucrose and EG. Further studies will be conducted to find the best method to preserve embryos for long term storage.     

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle,Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.     

Expression of heat shock protein 70a mRNA in Bombyx mori diapause eggs

In an effort to understand whether heat shock protein 70 (Hsp70) participates in the environmental 5 °C signal reception/transduction toward breaking embryonic diapause of the silkworm Bombyx mori, we isolated a cDNA for Hsp70a and examined the expression of Hsp70a mRNA in B. mori diapause and nondiapause eggs by quantitative real-time PCR. Hsp70a mRNA gradually increased in diapause eggs continuously kept at 25 °C after oviposition to maintain diapause. When diapause eggs were exposed to the diapause-terminating condition of 5 °C beginning at 2 days post-oviposition, Hsp70a mRNA increased beginning at 5 days post-cold treatment. Even in nondiapause eggs, Hsp70a mRNA increased slightly with exposure to 5 °C. These results suggest that Hsp70a is involved in reception/transduction of the diapause-terminating (5 °C) signal via gene activation. The expression patterns of Hsp70a mRNA are discussed in relation to those of the cold-response gene Samui.     

Diapause induction, maintenance and termination in the rice stem borer Chilo suppressalis (Walker)

The rice stem borer, Chilo suppressalis, enters facultative diapause as fully grown larvae in response to short-day conditions during the autumn. Our results showed that the critical night length for diapause induction in C. suppressalis was between 10 h 22 min and 10 h 45 min at 22, 25 and 28 °C, 11 h 18 min at 31 °C, and between 10 h 5 min and 10 h 20 min under field conditions (average temperature ranged from 27.2 to 30.7 °C). The diapause incidence declined in ultra-long nights (18-22 h scotophases) and DD, and increased in ultra-short nights (2-6 h scotophases) and LL. Moreover, we found that the third instar was the stage most sensitive to the photoperiod, and night length played an essential role in the initiation of diapause. Night-interruption experiments with a 1-h light pulse at LD 12:12 (light 12:dark 12) exhibited two troughs of diapause inhibition, with one occurring in early scotophase and the other in late scotophase. Field observations for six years showed that most larvae entered winter diapause in August in response to declining day lengths, despite the high temperatures prevailing during August. By periodically transferring the field-collected overwintering larvae to different photoperiods and temperatures, the results showed that photoperiod had a significant influence on diapause development during the early phase of diapause, while high temperature significantly accelerated the termination of larval diapause.     

The influence of temperature on the duration of egg development in West European grasshoppers (Orthoptera: Acrididae)

Summary The relationship between embryonic postdiapause development (PDD) and temperature in ten Acridid species was studied by culturing eggpods from diapause onwards at constant temperatures (ranging from 15.0° C to 37.5° C). In six species PDD was also studied at fluctuating temperatures (12 h at 27.5° C and 12 h at 13.0° C). The PDD duration was strongly temperature dependent in all species studied (Q₁₀ values between 3.0 and 4.1) and differed greatly between species. To assess whether these differences affect habitat determination, PDD duration was related to habitat microclimate. We found that species with a relatively long PDD are restricted to relatively warm grasslands, while species with a short PDD are also found in colder grasslands. Two species have a more limited occurrence than predicted from PDD duration. It is argued that the length of PDD (and consequently hatching date) is crucial to the completion of the annual cycle. The results are applicable to conservation of grasshoppers in grasslands subject to eutrophication. Here increase of vegetation density and height will lead to lower maximum temperatures in the egg environment (i.e. near the soil surface) and consequently to a delay in hatching and loss of thermophilous species. Grassland management rules are proposed that should aid conservation of these species.     

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.     

Diapause termination and thermal requirements for postdiapause development inAphelinus mali at constant and fluctuating temperatures

Diapause termination under natural and simulated overwintering conditions, the effect of subzero temperature on postdiapause development and the relationship between postdiapause development rate and constant and fluctuating temperatures was studied in a Dutch population ofAphelinus mali Hald. (Hymenoptera: Aphelinidae).The rate of diapause termination was similar in larvae overwintering under natural and simulated conditions. Most larvae had terminated diapause by the last week of February. Some female larvae may have remained in diapause until the end of March. The exposure of postdiapause larvae to –10°C for two weeks did not affect their survival or postdiapause development rate.PostdiapauseA. mali larvae could complete development and the adults emerge from their mummified aphid hosts at constant temperatures from 12 to 24°C. Although some larvae completed postdiapause development at 10°C, few emerged. The theoretical threshold temperature (t_o) for postdiapause development was 9.4°C and the thermal constant (K) 136.4 degree-days. K was 121.4 and 134.8 for first and 50% emergence, respectively.The number of heat units accumulating above 9.4°C to 1st and 50% emergence was similar under constant and fluctuating temperatures.

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Fin de la diapause et exigences thermiques pour le développement après la diapause d'Aphelinus mali soumis à des températures constantes ou à des thermopériodes

Résumé L'achèvement de la diapause en conditions naturelles ou simulant l'hiver, les effets des températures inférieures à zéro sur le développement après la diapause et les relations entre la vitesse de développement après la diapause et les températures constantes ou en thermopériodes ont été examinés sur des populations néerlandaises d'A. mali (Hymenop.; Aphélinidae).Les taux d'achèvement de la diapause de larves hivernantes étaient semblables en conditions naturelles ou simulées. La plupart des larves ont terminé leur diapause la dernière semaine de février. Quelques larves femelles sont restées en diapause jusqu'à fin mars. L'exposition pendant 2 semaines des larves sorties de diapause à –10 °C ne compromet pas leur survie ou leur taux de développement après la diapause.Les larves ayant diapause peuvent terminer leur développement et les adultes émerger des pucerons momifiés aux températures constantes comprises entre 12 et 24 °C. Bien que quelques larves achèvent leur développement à 10 °C, peu émergent. La température seuil théorique de développement après la diapause (t_o) a été de 9,4 °C et la constante thermique (K), 136,5 degrés-jours. Pour la première émergence et pour 50% d'émergences, les valeurs de K étaient respectivement: 121,4 et 134,8.Le nombre d'unités thermiques pour la première émergence et pour 50% d'émergences était le même à température constante ou avec une thermopériode.

     

Seasonal patterns of the thermal response in relation to sugar and polyol accumulation in overwintering adults of elm leaf beetle, Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola (Muller), is one of the key pests of elm trees that survive winter in reproductive diapause in sheltered locations. Overwintering adults of the elm leaf beetle showed a complex sugar/polyol cryoprotectant system. The major components of the multiple systems were glucose, myo-inositol and trehalose. In this study, we investigated the seasonal profile of low molecular weight compounds and glycogen in natural population and also in response to thermal constant regimes (5 and 15 °C). Among these components, a remarkable seasonal pattern of accumulation/depletion was observed in myo-inositol over the course of hibernation with the development of diapause progress. Incubating at 5 °C only elicited a strong response in myo-inositol synthesis during diapause. It suggests that the elm leaf beetle accumulates myo-inositol not only in relation to entering diapause but also in response to low temperatures and their interactions. The laboratory acclimation experiments showed that adults exposed to 15 °C had no chance for accumulation of low molecular weight carbohydrate even during diapause. The results of this study illustrated that overwintering adults of elm leaf beetle produce myo-inositol as the primary substance which plays a specific role in some biochemical adjustments in overwintering adults of X. luteola.     

Geographic variation in embryonic development time and stage of diapause in a grasshopper

Embryonic development times and the stage at which embryonic diapause occurs varied dramatically among 23 populations of the Melanoplus sanguinipes/ devastator species complex in California, USA. Grasshoppers were collected from a wide range of latitudes (32°57N to 41°20N) and altitudes (10m to 3031 m), spanning much of the variation in climatic conditions experienced by these insects in California. When reared in a common garden in the laboratory, total embryonic development times were positively correlated to the mean annual temperature of the habitat from which the grasshoppers were collected (varying from about 19 days to 32 days when reared at 27°C). These grasshoppers overwinter as diapausing eggs and the proportion of embryonic development completed prior to diapause was significantly higher in populations collected from cool habitats (>70%) than in populations collected from warm environments (<26%). The length of pre-diapause development time is determined by the stage of embryonic development at which diapause occurs, and varies considerably among populations of these grasshoppers; grasshoppers from warmer environments tend to diapause at very early stages of embryogenesis, while grasshoppers from cooler environments diapause at very late stages. The combined effect of variation in embryonic development times and variation in the stage at which diapause occurs results in a dramatic reduction in the time needed to hatch in the spring; populations from warm environments required up to 20 days (at 27°C) to hatch while populations from cool environments required as few as 5 days to complete embryonic development prior to hatching. Egg size also varied significantly among populations, but tended to be larger in populations with shorter embryonic development times. Significant family effects were observed for development time and stage of diapause, suggesting significant heritabilities for these traits, although maternal effects may also contribute to family level variation. We interpret these findings to support the hypothesis that embryonic development time and the stage of embryonic diapause have evolved as adaptations to prevailing season lengths in the study populations.     

Mixed oviposition in individual females of Gryllus firmus: Graded proportions of fast-developing and diapause eggs

Summary Eggs of field crickets (Gryllus spp.) held at 25±1°C hatch in 2–4 weeks (fast-developing eggs) or 5–28 weeks (diapause eggs). Most species lay but one type: at least 10 species lay only fast-developing eggs, and pennsylvanicus and ovisopis lay only diapause eggs. Gryllus firmus from Gainesville, Florida, lays both types, and individual females do so for as long as 8 weeks. The proportion of diapause eggs laid weekly by captive females exposed to outdoor photoperiods and temperatures varies seasonally from <5% (March–June) to ca. 50% (November–December). At outdoor temperatures in late fall some eggs that are presumptively fast-developing (at 25° C) enter diapause.Some firmus from Carolina Beach, North Carolina, lay both diapause and fast-developing eggs. Outdoor rearing experiments established that spring adults could result from fast-developing eggs of fall adults, refuting the hypothesis that spring and fall adults at that locality represent temporally isolated demes.High variance in hatching times for eggs laid by one female is appropriate to the unpredictable extremes of moisture and temperature that occur in the open, sandy habitats of G. firmus. Physiological mechanisms of the mixed oviposition and specific environmental determinants of the varying proportions are unknown.     

Geographic variation in diapause induction and termination of the cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Overwintering diapause in Helicoverpa armigera, a multivoltine species, is controlled by response to photoperiod and temperature. Photoperiodic responses from 5 different geographical populations showed that the variation in critical photoperiod for diapause induction was positively related to the latitudinal origin of the populations at 20, 22 and 25 °C. Diapause response to photoperiod and temperature was quite different between northern and southern populations, being highly sensitive to photoperiod in northern populations and temperature dependence in southern populations. Diapause pupae from southern population showed a significantly shorter diapause duration than from northern-most populations when they were cultured at 20, 22, 25, 28 and 31 °C; by contrast, overwintering pupae from southern populations emerged significantly later than from northern populations when they were maintained in natural conditions, showing a clinal latitudinal variation in diapause termination. Diapause-inducing temperature had a significant effect on diapause duration, but with a significant difference between southern and northern populations. The higher rearing temperature of 22 °C evoked a more intense diapause than did 20 °C in northern populations; but a less intense diapause in southern population. Cold exposure (chilling) is not necessary to break the pupal diapause. The higher the temperature, the quicker the diapause terminated. Response of diapause termination to chilling showed that northern populations were more sensitive to chilling than southern population.