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

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

Cold hardiness in immature stages and adults in the adult‐diapausing spider mite Stigmaeopsis longus

The cold hardiness of arthropods is an important characteristic associated with overwintering success. Cold‐tolerant stages affect overwintering strategy, especially in arthropods that continuously feed on evergreen host plants in temperate regions. However, cold hardiness to mildly low temperature is rarely investigated. In the present study, we estimate the stage‐specific cold hardiness of a population of the spider mite Stigmaeopsis longus (Saito) (Acari: Tetranychidae) occurring on evergreen Sasa bamboo in a temperate area (Kochi City, southwestern Japan). Individuals of each stage developing under diapause‐inducing conditions (LD 10 : 14 h at 20 °C) are maintained at 4 °C (approximating the mean daily minimum temperature for December in Kochi City) for 30 days (eggs are cooled immediately, without short‐day development first). They are then returned to the initial conditions to assess survival rates. The survival rate of adult females (i.e. the diapausing stage) is high (99.5%), as is that of adult males and deutonymphs of both sexes (84.2–98.7% and 89.7–89.8%, respectively). The survival rate of mobile immature stages tends to increase toward adulthood in both sexes, whereas the survival rate of the eggs and quiescent stages is extremely low (16–23% and 0–20%, respectively). The poor cold hardiness of the eggs and quiescent stages presumably prevents the normal development of immature individuals during winter.     

Over-wintering stage polymorphism of a bruchine beetle: geographical variation in optimal diapause strategy

Abstract.  1. Most temperate insects undergo diapause at a specific developmental stage to overcome severe winters. The bruchine beetle Bruchidius dorsalis in a warmer region in Japan, however, has diverse over-wintering stages – non-diapausing larvae, diapausing larvae, and diapausing adults, whereas in a cooler region, it over-winters only as the final instar larva or adult in diapause.
2. The geographical pattern of over-wintering stages in 12 populations was investigated over a wide range along the mainland of Japan. It revealed that a distinct geographical pattern of over-wintering stages exists in relation to temperature conditions. In regions with warmer climates, the proportion of non-diapausing larvae increased and B. dorsalis had a more complex over-wintering stage structure.
3. Life cycles were also compared between two areas of Japan by field experiments. In the cooler area, the first generation over-wintered in the diapausing larval or adult stage. Conversely, in the warmer area, diapause was induced later and some of the first-generation adults produced second-generation offspring before over-wintering.
4. Based on the geographical cline of climates and the differences in cold hardiness among stages, we can demonstrate that the over-wintering stage variation among and within populations results from an adaptive timing of diapause induction in each region, because the late larval or adult diapauses protect pupae or eggs – which unlike other stages are not cold hardy – from being produced late in the season.     

Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over-wintering at raised temperatures: indications of different sensitivities of spruce and pine

Long-term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two-year-old seedlings with the same pre-history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.     

RAPID COLD HARDENING PROVIDING HIGHER COLD TOLERANCE THAN COLD ACCLIMATION IN THE PINE NEEDLE GALL MIDGE THECODIPLOSIS JAPO‐NENSIS LARVAE*

Abstract The responses of overwintering larvae of the pine needle gall midge Thecodiplosis japonensis Uchida et Inouye to rapid cold hardening and cold acclimation were studied. A rapid cold hardening response is found in the 3rd instar larvae of T. japonensis. When overwintering larvae are transferred directly from 27°C to ‐ 15°C for 3 h, there is only 17.9% survival, whereas exposure to 4°C for 2 h prior to transfer to ‐ 15°C increases survival to 40.0%. The acquired cold tolerance is transient and is rapidly lost (after 15 min at 27°C). Rapid cold hardening is more effective in maintaining larval survival than cold acclimation. Different mechanisms are suggested to regulate the insect's cold hardiness under rapid cold hardening and cold acclimation.     

Supercooling and cold-hardiness in eggs of western and northern corn rootworms

Oviposition by northern corn rootworms, Diabrotica barberi Smith and Lawrence, and western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), key pests of corn in the Great Plains of the USA, occurs in the soil during late summer. Overwintering eggs are exposed to variable soil moisture and temperatures below ?5 °C. The winter mortality of eggs in the soil is a primary factor that determines the potential for larval injury to corn the following spring. Our studies aimed to determine the comparative supercooling capacities of northern and western corn rootworm eggs and to assess egg mortality following brief exposure to extreme low temperature, ranging from ?12.0 to ?21.5 °C, under three moisture regimes. Eggs of northern corn rootworm were supercooled to a temperature as low as ?27 °C, and survived supercooling to a greater extent than did western corn rootworm eggs. Moisture treatment prior to supercooling had little effect on northern corn rootworm eggs. Western corn rootworm eggs were more resistant than northern corn rootworm eggs to the effects of desiccation followed by supercooling. The survival of northern corn rootworm eggs was better than western corn rootworms under dry conditions, followed by exposure to temperatures of ?12.0 and ?17.5 °C, but was very low at ?21.5 °C, regardless of the moisture regime. The results suggest that moisture and temperature may interact in the soil environment to determine the overwintering survival of corn rootworms. It is evident from these studies that both rootworm species experience mortality at temperatures well above the supercooling points of the eggs, but that differences exist in the effects of substrate moisture treatments on the cold‐hardiness of eggs from the two species.     

False codling moth Thaumatotibia leucotreta (Lepidoptera,Tortricidae) larvae are chill‐susceptible

Abstract This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7°C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is ?11.5 ± 0.3°C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from ?15.6°C to ?17.4°C after larvae were fasted for 24 h. Twenty‐four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to ?17.2°C and ?18.2°C respectively. Inoculative freezing (by water contact) raised SCP from ?15.6°C to ?6.8°C which could have important implications for post‐harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life‐stage, at least over the short time‐scales investigated here. In conclusion, larvae of T. leucotreta are chill‐susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post‐harvest sterilization efficacy.     

Differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail,Papilio machaon (Lepidoptera: Papilionidae), from the Osaka population

To clarify differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail, Papilio machaon, we reared larvae from the Osaka population under photoperiods of 16 h light : 8 h dark (LD 16:8) (long day) or LD 12:12 (short day) at 20°C. We examined the relationship between food consumption and weight during the final larval stadium and pupae, and measured the pupal supercooling point (SCP). Although the ratio of assimilation to consumption did not differ significantly between photoperiods, the ratio of assimilation to pupal weight differed significantly between individuals reared under long and short days. All diapausing pupae were brown, whereas 56% of non‐diapausing pupae were green with the remainder brown. The mean pupal body length (L), dorsal width (W₁) and lateral width (W₂) were larger in non‐diapausing than in diapausing pupae, and the W₁/L and W₁/W₂ ratios differed significantly between non‐diapausing and diapausing pupae. SCP was approximately –20°C and did not differ among pupae 5, 15 and 30 days after pupation under long‐day conditions. However, under short‐day conditions, mean SCP gradually decreased, stabilizing at approximately –24 to –25°C by 30 days after pupation. After freezing, some diapausing pupae emerged as adults, whereas all non‐diapausing pupae died. Both egestion and assimilation were greater under long‐day conditions. The results revealed that pupae of this papilionid exhibit seasonal polyphenism in physiological and morphological traits. Energy from food appears to be expended on increasing cold hardiness in the overwintering generation and on reproduction in the non‐overwintering generation.     

Geographic variation in embryonic diapause,cold‐hardiness and life cycles in the migratory locust Locusta migratoria (Orthoptera: Acrididae) in China

To investigate geographic adaptation of the migratory locust Locusta migratoria in China, locusts were collected from six localities, ranging from 47.4°N to 19.2°N. Using offspring from the various populations, we compared embryonic diapause, reproductive traits, cold‐hardiness and adult body size. The incidence of embryonic diapause was influenced by the genetic makeup, parental photoperiod, and incubation temperature of the eggs. The northern strain (47.4°N) produced diapause eggs under all photoperiodic conditions, whereas the other strains produced a higher proportion of diapause eggs when exposed to a short photoperiod. The incubation temperature greatly influenced diapause induction. At a low temperature, all eggs entered diapause, even some of those from a tropical strain (19.2°N) in which no diapause was induced at high temperatures. Photoperiodic changes during the parental generation affected the incidence of embryonic diapause. Diapause intensity decreased with decreasing original latitude. Cold hardiness was compared by exposing eggs in diapause to either ?10 or ?20°C for various periods; the northern strain was more cold‐hardy than the southern strain, although some eggs in the tropical strain were probably not in a state of diapause. Adult body size and head width showed a complicated pattern of variation along the latitudinal gradient, whereas egg pod size (egg pod width and egg number) and hatchling weight tended to decrease with decreasing latitude. These results reveal that L. migratoria has adapted to local environments and that the latitudinal gradient appears to play an important role in shaping L. migratoria life cycle and development.     

Low temperature tolerance and starvation ability of the oak processionary moth: implications in a context of increasing epidemics

• 1 We investigated how modifications in winter and spring temperature conditions may affect the survival of a spring‐hatching Lepidoptera, the oak processionary moth Thaumetopoea processionea.
• 2 Supercooling and chilling injury experiments indicate that eggs are especially cold hardy at the start of the winter period, although this ability is reduced later in the season. In the spring, young larvae are sufficiently cold hardy to ensure no direct mortality as a result of late frosts.
• 3 A comparison of phenological models shows that neonate larvae may await the unfolding of new oak leaves for relatively long periods (e.g. 1–30 days). Under both low (4°C after 5 days at 16°C) and high temperature experimental scenarios (constant 16°C), the majority of neonate larvae can survive starvation for more than 2 weeks.
• 4 Larvae may also suffer from food depletion once their development has been initiated (e.g. during cold springs) if the threshold temperature for feeding is not reached for several consecutive days, or in the case of late frosts affecting foliage availability. When temperature is reduced to 4°C, developing larvae become inactive and do not feed anymore; their starvation survival capability is reduced to approximately 2 weeks (cold spring hypothesis). At 16°C, developing larvae that are deprived of food can only survive for 10 days (late frost hypothesis).
• 5 We conclude that, in the oak processionary moth, neonate larvae are relatively well adapted to early hatching relative to budburst, ensuring them the highest foliage quality for development. In some years, however, phenological asynchrony or cold spring conditions may affect the persistence of populations at the limits of the species' range.

     

Development ofDiatraea Saccharalis [Lep.: Pyralidae] at constant temperatures

At constant temperatures between 15.6 and 32°C the incubation time of eggs ofDiatraea saccharalis (F.) was reduced by each increase in temperature. At 34°C the time decreased. Highest (98.6%) and lowest (9.9%) egg hatch occurred at 26 and 34°C, respectively. Larvae completed development at temperatures ranging from 22 to 34°C; however, only 4.4% of the larvae pupated at 34°C. Duration of the larval stage at 30°C (♂=18.1 days; ♀=19.1 days) was ca. 14 days shorter than at 22°C. Maximum rate of development in the pupal stage occurred at 28°C (ca. 6.8 days), and a higher temperature increased developmental time and mortality. Adult longevity and egg production generally were reduced with increasing temperatures and egg production was highest at 24°C (729.8 eggs/ moth). As many as 7 larval stages occurred; but most larvae completed development in 5 stages, and none completed development in less than 5 stages. The female larval stage was ca. 1 day longer than that of males, and this difference occurred primarily in the 5th stage.     

Effect of cold acclimation and rapid cold-hardening on the survival of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) under cold stress

Spodoptera frugiperda is a highly invasive pest species that recently invaded Africa and Asia causing severe economic losses, primarily related to corn and rice crops. Temperature is one of the most important environmental factors that influence the invasion of pests into new habitats. However, little is known regarding the thermal tolerance characteristics of invasive S. frugiperda. Thus, we investigated the response of four developmental stages of S. frugiperda (i.e., eggs, third and sixth instar larvae, and pupae) to cold acclimation (CA) and rapid cold-hardening (RCH). All individuals suffered high mortality with 24-h temperature treatments at <?5°C and >35 °C. The CA treatment significantly increased the survival rate of the eggs and third instar larvae, although it did not affect the sixth instar larvae and it decreased the pupation rate. The RCH treatment at 5 °C for 5 h or 2 °C for 2 h increased the cold tolerance capabilities of the third and sixth instar larvae, respectively. Thus, the larval stage appears to be crucial for the cold tolerance of S. frugiperda. Our findings improve the current understanding of the cold tolerance characteristics of S. frugiperda and indicate its potential for survival in the newly invaded temperate regions of Asia.     

Cold tolerance of the invasive larch casebearer and implications for invasion success

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Plasticity in the timing of a major life‐history transition and resulting changes in the age structure of populations of the salamander Hynobius retardatus

Variation in age and size at life‐history transitions is a reflection of the diversifying influence of biotic or abiotic environmental change. Examples abound, but it is not well understood how such environmental changes influence the age structure of a population. I experimentally investigated the effects of water temperature and food type on age and body size at metamorphosis in larvae of the salamander Hynobius retardatus. In individuals grown at a cold temperature (15 °C) or given Chironomidae as prey, the time to metamorphosis was significantly prolonged, and body size at metamorphosis was significantly enlarged, compared with individuals grown at a warmer temperature (20 °C) or fed larvae. I also examined whether larval density (a possible indicator of cannibalism in natural habitats) generated variation in the age structure of natural populations in Hokkaido, Japan, where the climate is subarctic. Natural ponds in Hokkaido may contain larvae that have overwintered for 1 or 2 years, as well as larvae of the current year, and I found that the number of age classes was related to larval density. Although cool water temperatures prolong the larval period and induce later metamorphosis, in natural ponds diet‐based enhancement of development translated into a shorter larval duration and earlier metamorphosis. Geographic variation in the frequency of cannibalism resulted in population differences in metamorphic timing in H. retardatus larvae. It is important to understand how environmental effects are ultimately transduced through individual organisms into population‐level phenomena, with the population response arising as the summation of individual responses. Without a thorough comprehension of the mechanisms through which population and individual responses to environmental conditions are mediated, we cannot interpret the relationship between population‐level and individual‐level phenomena. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 100–114.     

Seasonal changes in glycerol content and cold hardiness in two ecotypes of the rice stem borer, Chilo suppressalis, exposed to the environment in the Shonai district, Japan

The rice stem borer, Chilo suppressalis, is divided into at least two ecotypes in Japan, the Shonai ecotype (SN) which is distributed in the northern part of Japan, and the Saigoku ecotype (SG) which is distributed in the southwestern region. Cold hardiness is positively correlated with the level of glycerol in both ecotypes. To investigate whether ecological distribution affects glycerol accumulation and cold hardiness development in these two ecotypes, overwintering larvae of the SN and SG ecotypes were concurrently exposed to the Shonai district. Obvious differences in the progress of glycerol accumulation and cold hardiness development in SN and SG larvae were found in early winter in the Shonai district. The levels of glycerol content and cold hardiness were low in October and high in January in both ecotypes, but those levels were different within this period (November and December) between ecotypes; the levels in SN larvae quickly reached their maximum, whereas, in SG larvae levels increased slowly. Under controlled conditions, the effect of the period of acclimation at 10 degrees C and subsequent low-temperature (5 degrees C) exposure on glycerol accumulation was investigated. These results indicated that glycerol accumulation in SN was stimulated by the progression of diapause termination, whereas a higher cumulative effect on glycerol production in SG was found when diapause was in a deep state.     

Tetraploid Induction by Inhibiting Mitosis I with Heat Shock, Cold Shock, and Nocodazole in the Hard Clam Mercenaria mercenaria (Linnaeus, 1758)

Tetraploid induction by inhibiting mitosis I with heat shock (32, 35, and 38°C), cold shock (1, 4, and 7°C), and nocodazole (0.02 to 1.6 mg/L) was investigated in the hard clam Mercenaria mercenaria. All treatments were applied to fertilized eggs about 5 min before the first cell division at 22 to 23°C, and lasted for 10, 15, and 20 min. Three replicates were produced for each treatment with different parents. The ploidy of resultant larvae and juveniles was determined with flow cytometry. Heat shock of 35 and 38°C was effective in inhibiting mitosis I, producing 54% to 89% tetraploid larvae. Heat shock of 32°C accelerated embryonic development without inhibiting mitosis or producing tetraploids. In all heat-shock groups, the survival to D-stage larvae was lower than in controls, suggesting that heat-shock treatments and tetraploidy were detrimental to larval development. At the juvenile stage, survivors from heat-shock groups contained no tetraploids. Cold shocks suspended the first cell division during the treatment, but produced no tetraploids in the 4°C and 7°C treatment groups. Cold shock of 1°C produced 31% tetraploid larvae in one replicate, with none surviving to juvenile stage. Nocodazole inhibited mitosis I at concentrations of 0.04 mg/L or higher, but did not produce tetraploids. This study indicates that heat shock is most effective in inducing tetraploids through mitosis I inhibition, although none of the induced tetraploids survived to juvenile stage.     

Variation in early developmental stages in two populations of an intertidal crab, Neohelice (Chasmagnathus) granulata

Duration of embryonic development, egg size, larval size at hatching, and starvation tolerance of the first zoeal stage were studied in an intertidal crab from the southwestern Atlantic, Neohelice (formerly Chasmagnathus) granulata. These reproductive traits were quantified comparing (a) two populations living in ecologically contrasting coastal habitats in Argentina, a brackish lagoon, Mar Chiquita, MC vs. an open marine habitat near San Antonio, Patagonia, SA, (b) beginning vs. end of the reproductive season, and (c) two temperatures during egg development (18 vs. 27°C). Eggs in an early stage of embryonic development were in both populations larger at the beginning than at the end of the season, and were consistently larger in the SA population. These size differences persisted through larval hatching, independent of the temperature during embryogenesis. At 18°C, eggs produced at the beginning of the season developed in both populations more rapidly than those from the end of the reproductive season, while the opposite trend was observed at 27°C. The stage duration of the zoea I was in both populations shorter at the beginning as compared to the end of the season. The nutritional flexibility of the zoea I stage was compared using as indices the point-of-reserve-saturation (PRS₅₀) and the point-of-no-return (PNR₅₀). The PRS₅₀ was consistently lower in larvae from SA than in those from MC. In the MC population, this index was lower at the beginning than at the end of the season, while no significant seasonal difference was observed in larvae from SA. The PNR₅₀ varied between temperatures of embryonic development and populations, showing also significant interactions between all three factors. The PRS₅₀ was on average lower, and the PNR₅₀ was higher, than values previously reported for N. granulata, suggesting a stronger nutritional flexibility in the larvae used in the present study. Our results indicate significant intraspecific variability among separate populations, seasonal variation, and carry-over effects of environmental conditions prevailing during the embryonic phase, all of which may affect the performance of the larval phase.     

Embryonic and larval development of a Japanese spinous loach,Cobitis takatsuensis

The embryonic and larval development ofCobitis takatsuensis, a mountain stream spinous loach, was surveyed by incubating artificially inseminated eggs. The mean diameter of the inflated eggs and mean total length of newly-hatched larvae were 2.7 mm and 5.7 mm, respectively. The eggs were spherical, transparent and unpigmented, with a pale yellow yolk and no oil globule. The daily cumulative temperature to hatching was estimated to be 70–110°C. day. Hatched larvae were unpigmented with outer gill filaments on their cheeks, as in otherCobitis species, but the melanophores were comparatively less obvious at each developmental stage. The larvae started feeding eleven days after hatching yolk absorption being completed sixteen days after hatching. All the fin rays were fully developed and the juvenile stage reached at 16 mm TL, 38 days after hatching. Embryonic and larval developmental traits ofC. takatsuensis, such as egg size, clutch size and larval pigmentation, were similar to the Korean species,Niwaella multifasciata, that lives in the upper reaches of the Nak-tong river, andN. delicata, which inhabits Japanese mountain streams, rather than to its congeners. Among cobitine fishes, the spawning of a small number of larger eggs yielding larger larvae without pigmentation, characteristics shared byC. takatsuensis, N. multifasciata andN. delicata, is attributable to adaptation to cold mountain streams.     

Effects of temperature,photoperiod and soil humidity on induction of pseudopupal diapause in the bean blister beetle Epicauta gorhami

Larvae of the bean blister beetle Epicauta gorhami Marseul (Coleoptera: Meloidae) feed on grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis in meloid beetles. The effects of temperature, photoperiod and soil humidity on larval development of E. gorhami are examined in a population in Miyazaki, Japan, using egg pods of Locusta migratoria L. as food. At lower temperatures (20 and 22.5 °C), all larvae become pseudopupae, regardless of the photoperiod. By contrast, at higher temperatures (27.5 and 30 °C), almost all larvae pupate at the end of the fourth instar, again regardless of the photoperiod. A long‐day photoperiodic response occurs only at an intermediate temperature (25 °C): under an LD 12 : 12 h photocycle, all larvae enter diapause, although the diapause incidence tends to decrease as the day length becomes longer. Pseudopupae are immobile and remain in diapause for ≥120 days when they are kept under the same conditions, except that diapause terminates within a relatively short time at 30 °C. Although lower soil humidity retards post‐feeding development, soil humidity has no effect on the diapause incidence. On the basis of the short developmental period and diapause avoidance under summer conditions, it is suggested that this beetle partially produces two generations a year in southwestern Japan.     

Induction of larval diapause in the blowfly, Calliphora vicina R.-D. (Diptera, Calliphoridae) under field and laboratory conditions

Field experiments conducted in the environs of St. Petersburg (Russia) with a local population of Calliphora vicina showed that induction of larval diapause under natural conditions was significantly dependent on day lengths and temperature. The maternal photoperiodic response had a distinct threshold: the first diapausing larvae hatched from the eggs laid in the middle of August when the day length was 16 h; at shorter photoperiods, the fraction of diapausing larvae depended only on temperature. At the mean temperature of 16°C, larval diapause was rarely recorded; at 12–13°C, about 50% of the larvae entered diapause; at 7–9°C, nearly all the larvae entered diapause. These results of the field experiments agree well with the parameters of photoperiodic and thermal responses studied in the laboratory at constant temperatures and photoperiods.