Rapid cold hardening in the predatory mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae)

A rapid cold hardening response was studied in diapause and non-diapause females of the predatory mite Euseius finlandicus. When laboratory reared diapause and non-diapause females were transferred and maintained from the rearing temperature of 20 degrees C for 2 h to -11.5 degrees C and -10 degrees C, 10 to 20% survived respectively. However, conditioning of diapause females for 4 h at a range of temperatures from 0 to 10 degrees C before their exposure for 2 h to -11.5 degrees C, increased survival to approximately 90%. Similarly, conditioning of non-diapause females for 4 h at 5 degrees C before their exposure for 2 h to -10 degrees C increased survival to 90%. A similar rapid cold hardening response in both diapause and non-diapause females was also induced through gradual cooling of the mites, at a rate of approximately 0.4 degrees C per min. The rapid increase in cold tolerance after prior conditioning of the mites to low temperatures, was rapidly lost when they returned to a higher temperature of 20 degrees C. Rapid cold hardening extended the survival time of diapause and non-diapause females at sub-zero temperatures. The cost of rapid cold hardening in reproductive potential after diapause termination was negligible. In non-diapause females, however, the increase in cold tolerance gained through gradual cooling could not prevent cold shock injuries, as both fecundity and survival were reduced.     

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.     

Cold shock injury and ecological costs of rapid cold hardening in the grain aphid Sitobion avenae (Hemiptera: Aphididae)

The ability of first instar nymphs and newly moulted pre-reproductive adults of the grain aphid S. avenae to rapidly cold harden was investigated. When nymphs reared at 20 degrees C were transferred directly to -8 degrees C for 3 h, there was 18% survival. This exposure was selected as the discriminating temperature. Maximum increases in survival were achieved by acclimating nymphs for 2 h at 0 degrees C and adults for 3 h at 0 degrees C, resulting in survival of 83% and 68%, respectively. Cooling nymphs from 10 to 0 degrees C at different rates (1, 0.1 and 0.05 degrees C min(-1)) also increased cold hardiness, with the slowest rate of 0.05 degrees C min(-1) conferring the highest survival following exposure to the discriminating temperature. Adult aphids also expressed a rapid cold hardening response but to a lesser extent, with survival increasing from 16% to 68% following 3 h at 0 degrees C. There were no 'ecological costs' associated with rapid cold hardening in terms of development, longevity or fecundity. The data support the hypothesis that rapid cold hardening can be induced during the cooling phase of natural diurnal temperature cycles, allowing insects to track daily changes in environmental temperatures.     

Rapid cold hardening and expression of heat shock protein genes in the B-biotype Bemisia tabaci

This paper describes the rapid cold hardening processes of the sweetpotato whitefly, Bemisia tabaci (Gennadius). It was found that all developmental stages of B. tabaci have the capacity of rapid cold hardening and the length of time required to induce maximal cold hardiness at 0 °C varies with stage. There was only 18.3% survival when adult whiteflies were transferred directly from 26 °C to -8.5 °C for 2 h. However, exposure to 0 °C for 1 h before transfer to -8.5 °C increased the survival to 81.2%. The whiteflies show "prefreeze" mortality when they were exposed to temperatures above the supercooling point (SCP), although the range of SCP of whiteflies is -26 °C to -29 °C. The rapid cold hardening had no effect on SCP and reduced the lower lethal temperature of adults from -9 °C to -11 °C. Rapid cold-hardened adults had a similar lifespan as the control group but deposited fewer eggs than nonhardened individuals. The expression profiles during cold hardening and recovery from this process revealed that HSP90 did not respond to cold stress. However, HSP70 and HSP20 were significantly induced by cold with different temporal expression patterns. These results suggest that the rapid cold hardening response is possibly advantageous to whiteflies that are often exposed to drastic temperature fluctuations in spring or autumn in northern China, and the expression of HSP70 and HSP20 may be associated with the cold tolerance of B. tabaci.     

Stress-induced accumulation of glycerol in the flesh fly, Sarcophaga bullata: evidence indicating anti-desiccant and cryoprotectant functions of this polyol and a role for the brain in coordinating the response

Nondiapausing larvae of the flesh fly, Sarcophaga bullata, responded to several forms of short-term environmental stress (low temperature, anoxia and desiccation) by accumulating glycerol. Elevation of this polyol, regardless of the type of stress that induced accumulation, conferred cold resistance: larvae with high glycerol levels were 3-4 times more tolerant of a 2h exposure to -10 degrees C than unstressed larvae. Protection against low temperature injury, as well as dehydration, was also attained by injection of exogenous glycerol into third instar larvae. This artificially induced cold hardiness was only temporary: when glycerol-injected larvae were exposed to -10 degrees C immediately after injection, survival was high, but none survived if they were injected and then held at 25 degrees C for 2 days before the -10 degrees C exposure. Larvae ligated behind the brain immediately after low temperature exposure failed to accumulate glycerol, but glycerol did accumulate in larvae ligated 6-24h after cold treatment, thus implying a critical role for the brain in initiating glycerol production. Interestingly, a much shorter exposure (2h) to low temperature was sufficient to reduce the maximum rate of water loss. Collectively, these observations suggest that multiple pathways may be exploited in response to stress: one pathway is most likely associated with rapid cold hardening (RCH) which generates immediate protection, and a second pathway remains activated for a longer period to enhance the initial protection afforded by glycerol.     

Relationship between rapid cold-hardening and cold acclimation in the eggs of the yellow-spotted longicorn beetle, Psacothea hilaris

Rapid cold-hardening (RCH) and cold acclimation (ACC) were examined in eggs of the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae). When eggs incubated at 25 degrees C were transferred directly to conditions of -22 degrees C for 2h, less than 30% survived, whereas exposure to 0 degrees C for 4h prior to transfer to -22 degrees C increased survival to nearly 60%. The rapidly enhanced cold tolerance (RCH) was transient and lost rapidly after 1h at 25 degrees C. Incubation at 15.5 degrees C for 9 days (ACC) also enhanced cold tolerance. Comparison of the cold tolerance of non-treated eggs and eggs pre-treated to give RCH, ACC, or ACC+RCH allowed the relationship between the two hardening processes to be determined. At a mild subzero temperature (-10 degrees C) an RCH effect was not detected, whereas only RCH is effective at the severest subzero temperature just above the SCP (-26 degrees C). At intermediate temperatures (-16, -22 and -25 degrees C), ACC and RCH enhanced survival in combination. Therefore, the two hardening processes have different physiological bases but operate concomitantly over a wide temperature range.     

Rapid cold hardening in the olive fruit fly Bactrocera oleae under laboratory and field conditions

A rapid cold hardening response was studied in females and males of the olive fruit fly Bactrocera (Dacus) oleae. When laboratory-reared females and males were transferred and maintained from the rearing temperature of 24 °C for 2 h to –6.5 °C approximately 5% survived. However, conditioning of both females and males for 2 h at various temperatures from 0 to 10 °C before their exposure for 2 h to –6.5 °C increased survival to 80 to 92%. A similar rapid cold hardening response in both females and males was also induced through gradual cooling of the flies at a rate of approximately 0.4 °C per min. The rapid increase in cold tolerance after prior conditioning of the flies to low temperatures, was rapidly lost when they returned to a higher temperature of 24 °C. In the field, in late February and early March, females and males were capable of a rapid cold hardening response. After exposure to the critical temperature they suffered a high mortality when tested in the afternoon and low mortality early in the morning on consecutive days, probably because of differences in the prevailing field temperatures a few hours before testing. This plasticity of cold tolerance gained through rapid cold hardening may allow the flies to survive during periods of the year with great fluctuation in circadian temperatures.     

Critical thermal limits,temperature tolerance and water balance of a sub-Antarctic caterpillar,Pringleophaga marioni (Lepidoptera: Tineidae)

Thermal tolerance, supercooling point, water balance and osmoregulatory ability of Pringleophaga marioni Viette (Lepidoptera: Tineidae) are investigated in this study. Field-fresh larvae had a mean CT(Min) (cold stupor) of -0.6 degrees C and a mean CT(Max) (heat coma) of 38.7 degrees C. The mean supercooling point of field-fresh individuals was -5.0 degrees C. Caterpillars showed 100% survival of freezing to -6.5 degrees C, but at -12 degrees C mortality rose to 100%. Survival of a 30h exposure to -6.0 degrees C was 80%, but declined to 30% in the 6-12h interval at -7.5 degrees C. No caterpillars survived for longer than 12h at -9.0 degrees C. Survival of high temperatures (35 degrees C and above) was poor. Tolerance of water loss (46% of fresh mass) and rates of water loss (1% fresh massh(-1)) were similar to those found in other mesic insects. P. marioni larvae were incapable of metabolizing lipids to replenish lost water and showed no haemolymph osmoregulatory ability. It is suggested that the preponderance of freeze tolerance in high-latitude southern hemisphere species may be associated with their occurrence in moist habitats, and that the "freeze tolerance" category be re-examined in the light of the range of strategies adopted by such arthropods.     

Anoxia blocks thermotolerance and the induction of rapid cold hardening in the flesh fly, Sarcophaga crassipalpis

Abstract. Anoxia induced by nitrogen or carbon dioxide, or hypoxic/hypobaric conditions generated by a partial vacuum sensitizes red-eye pharate adults of Sarcophaga crassipalpis Macquart to a high temperature exposure that is normally nonlethal (40C for 2–3 h). Thermotolerance induced by a2h exposure to 40C (under aerobic conditions) doubles the pharate adults' tolerance to 45C but provides no protection against a combined exposure to 45C and anoxia, and only modest protection against a combined exposure to 40C and anoxia. Under aerobic conditions, exposing pharate adults to 0C for 2 h increases their tolerance to -10C (rapid cold hardening). Rapid cold hardening at 0C is not induced under anoxia. These results imply that tolerance to high temperatures and rapid cold hardening are dependent on aerobic processes and suggest that certain forms of temperature stress can be further exacerbated with anoxia.     

Induction of rapid cold hardening by cooling at ecologically relevant rates in Drosophila melanogaster

Over a decade ago it was hypothesized that the rapid cold hardening process allows an organism's overall cold tolerance to track changes in environmental temperature, as would occur in nature during diurnal thermal cycles. Although a number of studies have since focused on characterizing the rapid cold hardening process and on elucidating the physiological mechanisms upon which it is based, the ecological relevance of this phenomenon has received little attention. We present evidence that in Drosophila melanogaster rapid cold hardening can be induced during cooling at rates which occur naturally, and that the protection afforded in such a manner benefits the organism at ecologically relevant temperatures. Drosophila melanogaster cooled at natural rates (0.05 and 0.1 degrees C min(-1)) exhibited significantly higher survival after one hour of exposure to -7 and -8 degrees C than did those directly transferred to these temperatures or those cooled at 0.5, or 1.0 degrees C min(-1). Protection accrued throughout the cooling process (e.g., flies cooled to 0 degrees C were more cold tolerant than those cooled to 11 degrees C). Whereas D. melanogaster cooled at 1.0 degrees C min(-1) had a critical thermal minimum (i.e., the temperature at which torpor occurred) of 6.5+/-0.6 degrees C, those cooled at an ecologically relevant rate of 0.1 degrees C min(-1) had a significantly lower value of 3.9+/-0.9 degrees C.     

Factors affecting the freeze tolerance of the hoverfly Syrphus ribesii (Diptera: syrphidae)

Larvae of Syrphus ribesii collected from overwintering sites in the U.K. are strongly freeze tolerant with 70% survival at -35 degrees C. The cold tolerance of laboratory reared insects increased with increasing periods of acclimation at 0 degrees C, with a concurrent rise in the supercooling point (SCP) from -6.8+/-0.1 to -5.1+/-0.3 degrees C. There was 50% survival in the most cold-hardy group 72h after brief exposures to -30 degrees C. The retention of gut contents caused a decrease in cold hardiness, with only 13% of larvae surviving 72h after exposure to -15 degrees C, with no subsequent pupation or emergence. Wet larvae had a significantly higher SCP (-5.0+/-0.2 degrees C) compared to dry larvae (-7.8+/-0.4 degrees C), although survival of larvae was similar in both groups. There was no nucleator activity in the haemolymph of field collected larvae. The importance of these findings are discussed in relation to the freeze tolerance strategy of S. ribesii.     

蠋蝽抗寒性对快速冷驯化的响应及其生理机制

快速冷驯化可以提高某些昆虫的耐寒性.为了探讨不同冷驯化诱导温度对蝎蝽抗寒性的影响及其生理机制,以室内人工饲养的第3代蝎蝽成虫为对象,利用热电偶、液相色谱分析等技术手段,测定了经15、10、4℃冷驯化4h和梯度降温(依次在15、10、4℃各驯化4h)冷驯化后,蠋蝽成虫过冷却点、虫体含水率及小分子碳水化合物、甘油和氨基酸含量,及其在不同暴露温度(0、-5、-10℃)下的耐寒性.结果表明:处理后暴露在-10℃时,梯度处理组和4℃冷驯化处理组的蝎蝽成虫存活率为58.3％,其他处理组及对照组(室温饲养)的存活率显著降低,平均为8.9％;梯度处理组与4℃冷驯化处理组蠋蝽成虫过冷却点平均为-15.6℃,比其他处理平均降低1.3℃;各处理虫体含水率无显著差异,平均为61.8％;与其他各组相比,梯度处理组和4℃冷驯化组蠋蝽成虫的葡萄糖、山梨醇和甘油含量分别增加2.82、2.65和3.49倍,丙氨酸和谷氨酸含量分别增加51.3％和80.2％,海藻糖、甘露糖和脯氨酸含量分别下降68.4％、52.2％和30.2％,而果糖含量各组间无显著差异.快速冷驯化对蠋蝽成虫具有临界诱导温度值,梯度降温驯化不能在快速冷驯化的基础上提高蠋蝽成虫的抗寒性.     

Effect of high and low temperatures on the drugstore beetle (Coleoptera: Anobiidae)

The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae), is a pest of stored medicinal and aromatic plants. Generally, mortality of each stage increased with an increase of temperature and exposure time. Heat tolerance for different stages from highest to lowest was young larvae, old larvae, eggs, adult, and pupae. The mortality after 7 h at 42 degrees C for young larvae, old larvae, eggs, adults, and pupae, respectively, was 16 +/- 5, 31 +/- 6, 48 +/- 3, 63 +/- 8, and 86 +/- 2% (mean +/- SEM). Similar trends for stage specific mortality were seen with the lethal time for 90% mortality (LT90) at 42 degrees C; 773, 144, 12, and 11 h for old larvae, eggs, adults, and pupa respectively. Mortality was too low with young larvae to estimate LT90. The LT90 for young larvae at 42, 45, 50, 55, and 60 degrees C was 25, 20, 3.9, 0.18, and 0.08 h, respectively. The cold tolerance of different stages at 0 degree C from highest to lowest was adults, old larvae, young larvae, pupae, and eggs. The LT90 at 0 degrees C was 298, 153, 151, 89, and 53 h, respectively. The LT90 for adults at 5, -5, -10, and -15 degrees C was 792, 58, 2, and 0.8 h, respectively. The supercooling point of adults was -15.2 +/- 2 degrees C; young larvae, -9.0 +/- 0.8 degrees C; old larvae, -6.5 +/- 0.5 degrees C; and pupae, -4.0 +/- 1.4 degrees C. Heat treatments that control young larvae should control all other stages of S. paniceum. Cold treatments that control adults should control all other stages of S. paniceum. Dried plants stored at 5 degrees C for 45 d or 42 degrees C for 30 h and then kept below 18 degrees C throughout the rest of the year, should remain pest-free without any chemical control.     

Hardening trumps acclimation in improving cold tolerance of Drosophila melanogaster larvae

Abstract Chill‐susceptible insects are able to improve their survival of acute cold exposure over both the short term (i.e. hardening at a relatively severe temperature) and longer term (i.e. acclimation responses at milder temperatures over a longer time frame). However, the mechanistic overlap of these responses is not clear. Four larval stages of four different strains of Drosophila melanogaster are used to test whether low temperature acclimation (10 °C for 48 h) improves the acute cold tolerance (LT₉₀, ～2 h) of larvae, and whether acclimated larvae still show hardening responses after brief exposures to nonlethal cold or heat, or a combination of the two. Acclimation results in increased cold tolerance in three of four strains, with variation among instars. However, if acclimation is followed by hardening pre‐treatments, there is no improvement in acute cold survival. It is concluded that short‐term thermal responses (e.g. hardening) may be of more ecological relevance to short‐lived life stages such as larvae, and that the mechanisms of low temperature hardening and acclimation in D. melanogaster may be antagonistic, rather than complementary.     

The influence of developmental stage on cold shock resistance and ability to cold-harden in Drosophila melanogaster

Thermal sensitivity and ability to rapidly cold- and heat-harden may change during ontogeny. This study reports how inherent cold tolerance and ability to rapidly cold-harden change across eight developmental stages in both genders of Drosophila melanogaster using a similar experimental approach for all stages. Inherent cold tolerance was estimated as LT50 by assaying cold shock survival over a wide range of temperatures (-16 to 5 degrees C). Rapid cold-hardening (RCH) was applied by cooling from 25 to 0 degrees C at -0.25 degrees C min(-1) followed by 1 h at 0 degrees C. Individuals were cold shocked either directly or after RCH to estimate the effect of RCH. We found large variation in cold tolerance among developmental stages and minor differences between genders. Eggs were most tolerant followed by adults, pupae and larvae. In the light of this and other studies it is suggested that there is a general pattern of stage specific thermal stress resistance in Drosophila. The capacity to rapidly cold-harden was found in both sexes of larval, pupal and adult stages, though some developmental stages showed negative or neutral effects of RCH which was probably due to the cost associated with the hardening treatment in these cold susceptible stages. The early presence of RCH indicates that the mechanisms behind hardening are not stage specific and that RCH may be an ecologically important trait in early stages of ontogeny.     

Rapid cold hardening increases cold and chilling tolerances more than acclimation in the adults of the sycamore lace bug, Corythucha ciliata (Say) (Hemiptera: Tingidae)

The sycamore lace bug, Corythucha ciliata is a new, invasive pest of Platanus trees in China. Although C. ciliata is often subjected to acute low temperatures in early winter and spring in northern and eastern China, the cold tolerance of C. ciliata has not been well studied. The objectives of this study were to determine whether adults of C. ciliata are capable of rapid cold hardening (RCH), and to compare the benefits of RCH vs. cold acclimation (ACC) in the laboratory. When the adult females incubated at 26 °C were transferred directly to the discriminating temperature (−12 °C) for 2 h, survival was only 22%. However, exposure to 0 °C for 4 h before transfer to −12 °C for 2 h induced RCH, i.e., increased survival to 68%. RCH could also be induced by gradual cooling of the insects at rates between 0.1 and 0.25 °C min⁻¹. The protection against cold shock obtained through RCH at 0 °C for 4 h was lost within 1 h if the adults were returned to 26 °C before exposure to −12 °C. Survival at both −12 and −5 °C was greater for RCH-treated than for ACC-treated adults (for ACC, adults were kept at 15 °C for 5 days), and the lethal temperature (2 h exposure) was lower for RCH-treated than for ACC-treated adults. The results suggest that RCH may help C. ciliata survive the acute low temperatures that often occur in early winter and early spring in northern and eastern China.     

Rapid responses to high temperature and desiccation but not to low temperature in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera,Tineidae)

A broad definition of rapid cold hardening (RCH) is that it is the process whereby insects increase their survival of a sub-zero temperature after a brief (h) pre-exposure to a less severe low temperature. The effects of various pre-treatments on survival of two h at -7.9 degrees C were investigated in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera: Tineidae), the first time RCH has been investigated in a freeze tolerant arthropod. All caterpillars froze when exposed to -7.9 degrees C, and none of the low temperature pre-treatments (-5, 0, 5 and 15 degrees C, as well as -5 degrees C and 0 degrees C with a delay before freezing) nor slow cooling (0.1 degrees C/min) elicited any improvement in survival of -7.9 degrees C as compared to controls. However, high temperature treatments (25, 30 and 35 degrees C), desiccation and acclimation for 5 days at 0 degrees C did result in significant increases in survival of the test temperature, possibly as a result of heat shock protein production. Haemolymph osmolality was elevated only by the 35 degrees C pre-treatment. It is suggested that the unpredictable environment of Marion Island means that P. marioni must always be physiologically prepared to survive cold snaps, and that this year-round cold hardiness therefore supersedes a rapid cold hardening response.     

Interactions between desiccation resistance,host-plant contact and the thermal biology of a leaf-dwelling sub-antarctic caterpillar,Embryonopsis halticella (Lepidoptera: Yponomeutidae)

During May 1997 thermal tolerance, supercooling point (SCP), low and high temperature survival, and desiccation resistance were examined in field-fresh Embryonopsis halticella Eaton larvae from Marion Island. SCPs were also examined in acclimated larvae, larvae starved for seven days, larvae within their leaf mines, and in larvae exposed to ice crystals. Field-fresh larvae had a critical minimum temperature (CT(Min)) and critical maximum temperature (CT(Max)) of 0 degrees C and 39.7 degrees C, respectively. Mean SCP of field-fresh caterpillars was -20.5 degrees C and this did not change with starvation. Field-fresh larvae did not survive freezing and their lower lethal temperatures (70% mortality below -21 degrees C) and survival of exposure to constant low temperatures (100% mortality after 12hrs at -19 degrees C) indicated that they are moderately chill tolerant. SCP frequency distributions were unimodal for field-fresh larvae, but became bimodal at higher acclimation temperatures. Contact with ice-crystals caused an increase in SCP (-6.5 degrees C), but contact with the host plant had less of an effect at higher subzero temperatures. It appears that the remarkable desiccation resistance of the larvae is selected for by the absence of a boundary layer surrounding their host plant, caused by constant high winds. This suggests that the low SCPs of E. halticella larvae may have evolved as a consequence of pronounced desiccation resistance.     

Cold hardiness,supercooling ability and causes of low-temperature mortality in the soft tick,Argas reflexus,and the hard tick,Ixodes ricinus (Acari: Ixodoidea) from Central Europe

Seasonal supercooling points (SCPs=temperature of crystallization) and cold hardiness were investigated in the indigenous hard tick, I. ricinus, and in A. reflexus, a soft tick introduced to Central Europe from the South. Both species proved to be freeze-susceptible as well as highly susceptible to inoculative freezing. None of the postembryonic developmental stages of either species showed any distinct seasonal pattern of SCP. Unexpectedly, the introduced A. reflexus exhibited a distinctly higher degree of cold hardiness in terms of lower lethal temperature (LT(50): 24h exposure) as well as lethal time (T(50): time of survival at -10.1 degrees C) than I. ricinus. Engorged I. ricinus larvae as well as engorged summer acclimatized A. reflexus larvae showed some mortality at temperatures well above the SCP. This mortality was generally expressed as a failure of the following stage to eclose properly. A 10-day cold acclimation at +3 degrees C eliminated that kind of mortality in summer acclimatized A. reflexus larvae, but not in I. ricinus larvae. It was frequently observed that freezing of ticks resulted-possibly via leakage from the midgut-in a subsequent reddish brown discoloration of the ticks after thawing. Taking into account that discoloration was an indication of previous freezing, it was concluded, that after long-term exposure (for >/=30 days) at -10.1 degrees C, a temperature well above the SCP, some tick mortality could be observed that was not caused by previous freezing. Weighing experiments clearly demonstrated, that the level of dehydration was not critical for survival of A. reflexus during long-term cold exposure, even at low RH. This indicates, that cold-related factors other than freezing and dehydration were detrimental to this species.     

Cold tolerance and cold hardening strategy of the Japanese pine sawyer Monochamus alternatus (Coleoptera: Cerambycidae)

The Japanese pine sawyer, Monochamus alternatus , is an important pine forest pest and vector transmitting the pine wilt nematode that causes pine wilt disease. Low temperatures in autumn, winter and spring often differentially affect mortality of M. alternatus larvae. In this paper, we mainly compared the differences of mortality and cold hardening of larvae from different seasons, based on supercooling point (SCP) and cumulative probability of individuals freezing (CPIF). The cold hardening of the larvae from autumn, winter and spring seasons were largely different. Correlations between mortality and CPIF of autumn and spring larvae were highest on day 1/4, and gradually decreased with prolonged exposure duration. This beetle's death mainly resulted from freezing in short exposure duration. However, the correlation between mortality and CPIF of winter larvae increased gradually with the prolonged exposure duration. Death did not mainly result from freezing in long exposure duration. Autumn larvae are more susceptible and adaptable than winter and spring larvae. Winter larvae have a slight freeze-tolerance trend. Our research showed that M. alternatus came into complex cold-hardening strategies under natural selection. Freeze avoidance is the primary strategy; with prolonged exposure duration to above SCP or < 0 °C, chill tolerance is more important; this is followed by freeze tolerance during harsh winters.