Effect of cooling rates on the cold hardiness and cryoprotectant profiles of locust eggs

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse

Insect performance is linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine and polar species. To overwinter, insects have adapted a range of strategies to become truly cold hardy. However, although the mechanisms underlying the ability to avoid or tolerate freezing have been well studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this limiting cold tolerance for insects susceptible to mild chilling. Here, we investigated how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoidant mountain pine beetle (Dendroctonus ponderosae) larvae in autumn, mid-winter and spring, and related it to organismal recovery times and survival. Hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the 7-day experiment. The degree of ionoregulatory collapse correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during extensive cold exposures, where hemolymph K+ concentration was highest, and a sigmoidal relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to that of chill-susceptible insects, albeit at much lower temperatures. Based on these results, we propose that a prerequisite for the evolution of insect freeze avoidance may be a convergent or ancestral ability to maintain ion homeostasis during extreme cold stress.

Differential Cold Tolerance on Immature Stages of Geographically Divergent Ceratitis capitata Populations

Cold tolerance of adult medflies has been extensively studied but the effect of subfreezing temperatures on the immature stages remains poorly investigated, especially as far as different populations are regarded. In this study, we estimated the acute cold stress response of three geographically divergent Mediterranean fruit fly populations originating from Greece (Crete, Volos) and Croatia (Dubrovnik) by exposing immature stages (eggs, larvae, pupae) to subfreezing temperatures. We first determined the LT50 for each immature stage following one hour of exposure to different temperatures. Then eggs, larvae and pupae of the different populations were exposed to their respective LT50 for one hour (LT50 = -11 °C, LT50 = -4.4 °C, LT50 = -5 °C for eggs, larvae and pupae, respectively). Our results demonstrate that populations responded differently depending on their developmental stage. The population of Dubrovnik was the most cold-susceptible at the egg stage, whereas in that of Crete it was at the larval and pupal stage. The population of Volos was the most cold-tolerant at all developmental stages. The egg stage was the most cold-tolerant, followed by pupae and finally the 3rd instar wandering larvae. This study contributes towards understanding the cold stress response of this serious pest and provides data for important parameters that determine its successful establishment to unfavorable environments with an emphasis on range expansion to the northern, more temperate regions of Europe.

Elucidating the Effect of Temperature Stress on the Protein Content, Total Antioxidant Capacity, and Antioxidant Enzyme Activities in Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae Koch is a worldwide agricultural pest mite that feeds on more than 1100 kinds of crops. The mite has developed a high level of tolerance to high temperatures, but the physiological mechanism underlying the outstanding adaptability of this pest to high temperatures remains unclear. To clarify the physiological mechanisms of T. urticae in response to short-term heat stress, four temperatures (36, 39, 42, and 45 °C) and three short-term heat durations (2, 4, and 6 h) were conducted to test the effects on protein content, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the total antioxidant capacity (T-AOC). The results showed that protein content, antioxidant enzyme activity, and T-AOC in T. urticae were significantly induced by heat stress. These results suggest that heat stress induces oxidative stress and that antioxidant enzymes play an important role in reducing oxidative damage in T. urticae. The data of this study will provide a basis for further research on the molecular mechanisms of thermostability and ecological adaptability of T. urticae.

Effects of short-term heat stress on the activity of three antioxidant enzymes of predatory mite Neoseiulus barkeri (acari, phytoseiidae)

To study the physiological mechanisms of Neoseiulus barkeri in response to short-term heat stress, the eggs and the emerged adults were exposed to 38, 40, and 42°C, 85% ± 5%RH,16 h:8 h (L:D) for 2, 4, and 6 h. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) as well as the protein content of N. barkeri were examined. All treatments caused significant different changes compared to the untreated control. The protein content increased as the temperature increased, while it showed different changing trends with the prolongation of exposure duration. The enzymatic activity of SOD, CAT, and POD was significantly affected by the temperature treatment. Both the maximum and minimum level of the three enzymes after a short-term heat stress differed significantly to the control group (p < 0.05). The highest values of three enzymatic activities were all obtained at 40°C-4 h. Person correlation analysis indicates that the high temperature was the primary factor affecting the enzymatic activity, while the exposure duration of the heat stress was the secondary factor. In general, the short-term heat stress increased the protein content of Neoseiulus barkeri and up-regulated the expression of SOD, CAT, and POD activities as well.

Antioxidant Enzymes and Heat Shock Protein Genes from Liposcelis bostrychophila Are Involved in Stress Defense upon Heat Shock

Simple Summary

Liposcelis bostrychophila is one of the most serious pests of stored commodities among the psocids. Controlling psocids mainly relies on chemical insecticides and heat stress. In fact, L. bostrychophila has developed high levels of resistance or tolerance to heat treatment in grain storage systems. In this study, we evaluated the changes in malondialdehyde (MDA) concentration after different high temperatures. The result showed that MDA is increased slightly overall, but a drastic increase is detected at 42.5 °C for exposure of different times. To further explore the principles of L. bostrychophila in response to heat stress, we tested the changes of superoxide dismutase (SOD), catalase (CAT), peroxidases (POD) and glutathione-S-transferases (GST) activities under different heat treatments and identified four inducible LbHsp70 genes and one LbHsp110 gene. Enzyme activities and transcript levels changed drastically after different heat treatments. These findings contribute to our understanding of the mechanism of L. bostrychophila responding to heat stress and provide baseline information for further understanding the excellent targets of L. bostrychophila.

Abstract

Psocids are a new risk for global food security and safety because they are significant worldwide pests of stored products. Among these psocids, Liposcelis bostrychophila has developed high levels of resistance or tolerance to heat treatment in grain storage systems, and thus has led to investigation of molecular mechanisms underlying heat tolerance in this pest. In this study, the time-related effects of thermal stress treatments at relatively high temperatures on the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-S-transferases (GST) and malondialdehyde (MDA), of L. bostrychophila were determined. Thermal stress resulted that L. bostrychophila had a significantly higher MDA concentration at 42.5 °C, which indicated that the heat stress increased lipid peroxidation (LPO) contents and oxidative stress in this psocid pest. Heat stress also resulted in significant elevation of SOD, CAT and GST activities but decreased POD activity. Our data indicates that different antioxidant enzymes contribute to defense mechanisms, counteracting oxidative damage in varying levels. POD play minor roles in scavenging deleterious LPO, while enhanced SOD, CAT and GST activities in response to thermal stress likely play a more important role against oxidative damage. Here, we firstly identified five LbHsps (four LbHsp70s and one LbHsp110) from psocids, and most of these LbHsps (except LbHsp70-1) are highly expressed at fourth instar nymph and adults, and LbHsp70-1 likely presents as a cognate form of HSP due to its non-significant changes of expression. Most LbHsp70s (except LbHsp70-4) are significantly induced at moderate high temperatures (<40 °C) and decreased at extreme high temperatures (40–45 °C), but LbHsp110-1 can be significantly induced at all high temperatures. Results of this study suggest that the LbHsp70s and LbHsp110 genes are involved in tolerance to thermal stress in L. bostrychophila, and antioxidant enzymes and heat shock proteins may be coordinately involved in the tolerance to thermal stress in psocids.

Effect of Short-Term Low Temperature on the Growth, Development, and Reproduction of Bactrocera tau (Diptera: Tephritidae) and Bactrocera cucurbitae

The fruit flies Bactrocera tau (Walker) and B. cucurbitae (Coquillett) are economically important invasive pests on numerous vegetable and fruit species in China. Due to the instability of the early spring climate, temperatures often deviate far below the normal temperature for short periods of time. Such a sudden short-term low temperature may impact the reproduction and development of the two fruit fly species. In this study, the effects of low temperatures (8, 6, 4, 2, 0, -2, and -4°С) on the development and reproduction of these two closely related fruit fly species were studied under laboratory condition. The results showed that their survival rates decreased gradually with corresponding decreases in the tested temperatures. On the other hand, their pre-oviposition periods and their adult female to male sex ratios increased, while the average number of eggs per female of each species and longevity of male adult of B. cucurbitae initially increased and later decreased after exposure to the low-temperature treatments. Overall, low temperatures promoted reproduction in B. cucurbitae and B. tau at temperatures ranging from 24°С to as low as 8°С. Development and reproduction of the two species were negatively affected when temperatures were between 8 to -4°С. The cold resistance of each developmental stage was higher in B. tau than in corresponding stages of B. cucurbitae.

Response to Short-Term Cold Storage for Eggs of Agasicles hygrophila (Coleoptera: Chrysomelidae), a Biological Control Agent of Alligator Weed Alternanthera philoxeroides (Caryophyllales: Amaranthaceae)

The alligator weed flea beetle, Agasicles hygrophila Selman & Vogt (Coleoptera: Chrysomelidae) has been used very successfully for the biological control of the widely-distributed invasive weed Alternanthera philoxeroides (Mart.) Griseb (Caryophyllales: Amaranthaceae). In order to extend the 'shelf life' of natural enemies released in biological control programs, cold storage has proven to be a valuable commercial procedure. To determine a suitable low temperature for storage of A. hygrophila, we conducted short-term cold storage treatments of eggs (4°C for 0.5, 1, 2, 5 d, and 7.5, 10, 15°C for 5 d and a control of 25°C; all eggs were returned to 25°C after the treatments). We evaluated the effects of these treatments on the subsequent fitness of the populations based on a demographic analysis using group-reared age-stage two-sex life tables. For 5 d storage, temperatures below 10°C had lethal effects, which were also observed at 4°C for 2 d storage. Storage at 4°C for 0.5 d did not affect the fitness of A. hygrophila, but it did not prolong the developmental time. Storage at 10°C for 5 d significantly decreased rates of population increase compared with 25°C. A. hygrophila stored at 15°C for 5 d had similar age-(stage) specific survival rates, rates of population increase, increased longevity and reproductive capability to the controls at 25°C. It is concluded that there were no significant fitness costs after 5 d storage at 15°C, which is therefore potentially a suitable storage temperature for A. hygrophila eggs.

Heritability and Evolutionary Potential Drive Cold Hardiness in the Overwintering Ophraella communa Beetles

Chill tolerance plays a crucial role that allows insect species to adapt to cold environments. Two Chinese geographical populations (Laibin and Yangzhou populations) were selected to understand the chill resistance and evolutionary potential in the Ophraella communa, a biological control agent of the invasive common ragweed, Ambrosia artemisiifolia. Super-cooling point assays, knockdown tests under static low-temperature conditions and determination of glycerol content were studied. ANOVAs indicated significant differences regarding chill coma recovery time, super-cooling point, and glycerol content across populations and sexes. The narrow-sense heritability (h²) estimates of cold resistance based on a parental half-sibling breeding design ranged from 0.39 to 0.53, and the h² value was significantly higher in the Yangzhou population than in the Laibin population. Additive genetic variances were significantly different from zero for cold tolerance. The Yangzhou population of O. communa has a strong capability to quickly gain resistance to cold. We conclude that the O. communa beetle has a plasticity that can provide cold resistance in the changing climate conditions.

Better cold tolerance of Bt-resistant Spodoptera exigua strain and the corresponding cold-tolerant mechanism

Spodoptera exigua is a secondary target pest of Bt cotton commercialized in China. With the continuous adoption of Bt cotton, populations of S. exigua have gradually increased. However, the cold tolerance ability of Bt-resistant S. exigua and the effect of continuous Bt diet on anti-cold materials are unknown. In our study, it was found that Bt-resistant S. exigua (Bt10) developed better with shorter larval and pupal duration and higher pupation rate compared to CK at the suboptimal low temperature. The supercooling points and freezing points of the Bt-resistant S. exigua strain were determined, and body water content and anti-cold materials such as total sugar, trehalose and glycogen, glycerol and fat were examined to explore the effect of Bt toxin on overwintering and on population increase. The results showed that the supercooling point and the freezing point of the Bt-resistant S. exigua pupae were both significantly lower than that of the Bt-susceptible strain. No difference was found in the body water content of pupae and adults between the two strains. Total sugar content of the Bt-resistant strain at both the pupal and adult stages was higher than that of the susceptible strain at the corresponding stages, and glycogen content of the Bt-resistant strain at the larval stage was higher than that of the susceptible larval S. exigua. Fat content of the Bt-resistant larvae, pupae and adults was for each higher than that of the susceptible strain, but the difference was not significant except for that of the 3rd instar larvae. Glycerol content of the Bt-resistant strain at larval, pupal and adult stages was for each higher than that of the corresponding life stages of the susceptible strain. It can be seen that more glycerol was accumulated in Bt-resistant S. exigua. The results indicate that Bt-resistant S. exigua has better cold tolerance. The contents of the anti-freeze substances of progeny, especially glycerol, were increased after previous generations were continuously fed on Bt protein, which means that the Bt-resistant secondary target pests could more easily overcome the overwinter season and become a source of crop damage the following year.

Transcriptomic and proteomic analysis of pre-diapause and non-diapause eggs of migratory locust, Locusta migratoria L. (Orthoptera: Acridoidea)

Low temperature induces diapause in locusts. However, the physiological processes and initiation mechanism of diapause are not well understood. To understand the molecular basis of diapause, ‘omics’ analyses were performed to examine the differences between diapause and non-diapause eggs at both transcriptional and translational levels. Results indicated that a total of 62,241 mRNAs and 212 proteins were differentially expressed. Among them, 116 transcripts had concurrent transcription and translation profiles. Up-regulated genes related to diapause included glutathiones-S-transferase et al., and down-regulated genes including juvenile hormone esterase-like protein et al. KEGG analysis mapped 7,243 and 99 differentially expressed genes and proteins, to 83 and 25 pathways, respectively. Correlation enriched pathways indicated that there were nine identical pathways related to diapause. Gene Ontology analysis placed these genes and proteins into three categories, and a higher proportion of genes related to metabolism was up-regulated than down-regulated. Furthermore, three up-regulated pathways were linked to cryoprotection. This study demonstrates the applicability of high-throughput omics tools to identify molecules linked to diapause in the locust. In addition, it reveals cellular metabolism in diapause eggs is more active than in non-diapause eggs, and up-regulated enzymes may play roles in cryoprotection and storing energy for diapause and post-diapause stages.

Antioxidant responses of Propylaea japonica (Coleoptera: Coccinellidae) exposed to high temperature stress

Temperature is one of the most important environmental factors, and is responsible for a variety of physiological stress responses in organisms. Induced thermal stress is associated with elevated reactive oxygen species (ROS) generation leading to oxidative damage. The ladybeetle, Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae), is considered a successful natural enemy because of its tolerance to high temperatures in arid and semi-arid areas in China. In this study, we investigated the effect of high temperatures (35, 37, 39, 41 and 43 °C) on the survival and activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-S-transferases (GST), and total antioxidant capacity (TAC) as well as malondialdehyde (MDA) concentrations in P. japonica adults. The results indicated that P. japonica adults could not survive at 43 °C. CAT, GST and TAC were significantly increased when compared to the control (25 °C), and this played an important role in the process of antioxidant response to thermal stress. SOD and POD activity, as well as MDA, did not differ significantly at 35 and 37 °C compared to the control; however, there were increased levels of SOD, POD and MDA when the temperature was above 37 °C. These results suggest that thermal stress leads to oxidative stress and antioxidant enzymes play important roles in reducing oxidative damage in P. japonica adults. This study represents the first comprehensive report on the antioxidant defense system in predaceous coccinellids (the third trophic level). The findings provide useful information for predicting population dynamics and understanding the potential for P. japonica as a natural enemy to control pest insects under varied environmental conditions.

Effects of thermal stress on lipid peroxidation and antioxidant enzyme activities of the predatory mite, Neoseiulus cucumeris (Acari: Phytoseiidae)

Changes in temperature are known to cause a variety of physiological stress responses in insects and mites. Thermal stress responses are usually associated with the increased generation of reactive oxygen species (ROS), resulting in oxidative damage. In this study, we examined the time-related effect (durations for 1, 2, 3, and 5 h) of thermal stress conditions-i.e., relatively low (0, 5, 10, and 15 °C) or high (35, 38, 41, and 44 °C) temperatures-on the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), glutathione S-transferases (GSTs), and total antioxidant capacity (T-AOC) of the predatory mite Neoseiulus cucumeris. Also the lipid peroxidation (LPO) levels of the predatory mite were measured under thermal stress conditions. The results confirmed that thermal stress results in a condition of so-called oxidative stress and the four antioxidant enzymes play an important role in combating the accumulation of ROS in N. cucumeris. CAT and POX activity changed significantly when the mites were exposed to cold and heat shock, respectively. The elevated levels of SOD and GSTs activity, expressed in a time-dependent manner, may have an important role in the process of antioxidant response to thermal stress. However, the levels of LPO in N. cucumeris were high, serving as an important signal that these antioxidant enzyme-based defense mechanisms were not always adequate to counteract the surplus ROS. Thus, we hypothesize that thermal stress, especially extreme temperatures, may contribute much to the generation of ROS in N. cucumeris, and eventually to its death.

Genome wide gene-expression analysis of facultative reproductive diapause in the two-spotted spider mite Tetranychus urticae

BACKGROUND

Diapause or developmental arrest, is one of the major adaptations that allows mites and insects to survive unfavorable conditions. Diapause evokes a number of physiological, morphological and molecular modifications. In general, diapause is characterized by a suppression of the metabolism, change in behavior, increased stress tolerance and often by the synthesis of cryoprotectants. At the molecular level, diapause is less studied but characterized by a complex and regulated change in gene-expression. The spider mite Tetranychus urticae is a serious polyphagous pest that exhibits a reproductive facultative diapause, which allows it to survive winter conditions. Diapausing mites turn deeply orange in color, stop feeding and do not lay eggs.

RESULTS

We investigated essential physiological processes in diapausing mites by studying genome-wide expression changes, using a custom built microarray. Analysis of this dataset showed that a remarkable number, 11% of the total number of predicted T. urticae genes, were differentially expressed. Gene Ontology analysis revealed that many metabolic pathways were affected in diapausing females. Genes related to digestion and detoxification, cryoprotection, carotenoid synthesis and the organization of the cytoskeleton were profoundly influenced by the state of diapause. Furthermore, we identified and analyzed an unique class of putative antifreeze proteins that were highly upregulated in diapausing females. We also further confirmed the involvement of horizontally transferred carotenoid synthesis genes in diapause and different color morphs of T. urticae.

CONCLUSIONS

This study offers the first in-depth analysis of genome-wide gene-expression patterns related to diapause in a member of the Chelicerata, and further adds to our understanding of the overall strategies of diapause in arthropods.

Cold temperatures increase cold hardiness in the next generation Ophraella communa beetles

The leaf beetle, Ophraella communa, has been introduced to control the spread of the common ragweed, Ambrosia artemisiifolia, in China. We hypothesized that the beetle, to be able to track host-range expansion into colder climates, can phenotypically adapt to cold temperatures across generations. Therefore, we questioned whether parental experience of colder temperatures increases cold tolerance of the progeny. Specifically, we studied the demography, including development, fecundity, and survival, as well as physiological traits, including supercooling point (SCP), water content, and glycerol content of O. communa progeny whose parents were maintained at different temperature regimes. Overall, the entire immature stage decreased survival of about 0.2%-4.2% when parents experienced cold temperatures compared to control individuals obtained from parents raised at room temperature. However, intrinsic capacity for increase (r), net reproductive rate (R 0) and finite rate of increase (λ) of progeny O. communa were maximum when parents experienced cold temperatures. Glycerol contents of both female and male in progeny was significantly higher when maternal and paternal adults were cold acclimated as compared to other treatments. This resulted in the supercooling point of the progeny adults being significantly lower compared to beetles emerging from parents that experienced room temperatures. These results suggest that cold hardiness of O. communa can be promoted by cold acclimation in previous generation, and it might counter-balance reduced survival in the next generation, especially when insects are tracking their host-plants into colder climates.

Identification and characterization of a gene encoding a UBX domain-containing protein in the migratory locust, Locusta migratoria manilensis

Ubiquitin regulatory X (UBX) domain-containing proteins are believed to function as cofactors for p97/CDC48, an adenosine triphosphatase shown to be involved in multiple cellular processes. In the present study, a full-length complementary DNA (cDNA) of UBX domain-containing gene, termed LmUBX1, was cloned from Locusta migratoria manilensis and characterized, using random amplification of cDNA ends polymerase chain reaction (RACE PCR), sequence analysis and quantitative real-time PCR. LmUBX1, 1 600 bp in length, is predicted to encode a 446-amino acid protein with a predicted molecular weight of 51.18 kDa that contains a central PUB domain and a carboxy-terminal UBX domain. Homology analysis revealed that LmUBX1 has higher similarity to the known UBX domain-containing proteins from insects than from other species. Moreover, based on sequence characteristics and phylogenetic relationships, it is suggested that LmUBX1 can be classified into the UBXD1 subfamily. Expression analysis founded that LmUBX1 exhibited significant expression variations at different developmental stages and in different tissues, suggesting that the expression of LmUBX1 was highly regulated. Interestingly, its messenger RNA transcript was more abundant in ovary and testis than in other tissues examined, suggesting that it may have more important roles in the reproductive system. In addition, LmUBX1 was differentially expressed in gregarious and solitary locusts and was significantly up-regulated in third and fifth instars of gregarious locusts, implying that LmUBX1 was also likely involved in the phase polyphenisms in L. migratoria manilensis. To our knowledge, this is the first report of cloning of a full-length cDNA of UBX domain-containing gene from L. migratoria manilensis.

Rapid cold hardening improves recovery of ion homeostasis and chill coma recovery in the migratory locust Locusta migratoria

Chill tolerance of insects is defined as the ability of insects to tolerate low temperature under circumstances not involving freezing of intra- or extracellular fluids. For many insects chill tolerance is crucial for their ability to persist in cold environments and mounting evidence indicate that chill tolerance is associated with the ability to maintain ion- and water-homeostasis, thereby ensuring muscular function and preventing chill injury at low temperature. The present study describes the relationship between muscle and hemolymph ion-homeostasis and time to regain posture following cold shock (CS, 2h at -4°C) in the chill susceptible locust, Locusta migratoria. This relationship is examined in animals with and without a prior rapid cold hardening treatment (RCH, 2h at 0°C) to investigate the physiological underpinnings of RCH. Cold shock elicited a doubling of hemolymph [K+] and this disturbance was greater in locusts pre-exposed to RCH. Recovery of ion homeostasis was, however, markedly faster in RCH treated animals which correlated well with whole organism performance as hardened individuals regained posture more than 2 minutes faster than non-hardened individuals following CS. The present study indicates that loss and recovery of muscular function is associated with resting membrane potential of excitable membranes as attested from the changes in the equilibrium potential for K+ (EK) following CS. Both hardened and non-hardened animals recovered movement once K+ homeostasis was recovered to a fixed level (EK≈ -41 mV). RCH is therefore not associated with altered sensitivity to ion disturbance but instead a faster recovery of hemolymph [K+].

Antioxidant responses of citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), exposed to thermal stress

Relatively low or high temperatures are responsible for a variety of physiological stress responses in insects and mites. Induced thermal stress was recently associated with increased reactive oxygen species (ROS) generation, which caused oxidative damage. In this study, we examined the time-related effect of the relatively low (0, 5, 10, and 15 °C) or high (32, 35, 38, and 41 °C) temperatures on the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidases (POX), and glutathione-S-transferase (GST), and the total antioxidant capacity (TEAC) of the citrus red mite, Panonychus citri (McGregor). The malondialdehyde (MDA) concentration, as a marker of lipid peroxidation in organisms, was also measured in the citrus red mite under thermal stress conditions. Results showed that SOD and GST activities were significantly increased and play an important role in the process of antioxidant response to thermal stress. Lipid peroxidation levels increased significantly (P<0.001) and changed in a time-dependent manner. CAT and POX activity, as well as TEAC, did not vary significantly and play a minor role to remove the ROS generation. These results suggest that thermal stress leads to oxidative stress and antioxidant enzymes play an important role in reducing oxidative damage in the citrus red mite.

Geographic differences on accumulation of sugars and polyols in locust eggs in response to cold acclimation

The accumulation of low molecular weight sugars and polyols is one of major mechanisms hypothesized to increase cold tolerance in overwintering insects. But little is known about whether these sugars and polyols are involved in geographic variation of cold tolerance. In this study, we investigated accumulation patterns of eight low molecular weight sugars and polyols of eggs in tropical and temperate populations of the migratory locust, which exhibits between-population variation in cold tolerance, in response to cold acclimation (5, 0 and -5 degrees C). Excluding erythritol, the other seven carbohydrates were identified as possible cryoprotectants in locust eggs. Basal maximal and minimal concentrations were 45 microg/g wet weight for trehalose and 0.59 microg/g wet weight for glycerol. Most sugars and polyols were elevated after a -5 degrees C exposure. In a tropical population, fructose, glucose, sorbitol and myo-inositol were significantly accumulated by low temperature treatments, but glycerol was not. In the temperate population, glycerol, glucose, mannitol, sorbitol, myo-inositol were significantly accumulated but trehalose did not increase. Our results suggest different accumulation patterns of these carbohydrates of locust eggs between tropical and temperate populations and highlighted possible roles for them in geographic variation of cold tolerance in the migratory locust.

Characterization of the heat shock protein 90 gene in the plant parasitic nematode Meloidogyne artiellia and its expression as related to different developmental stages and temperature

The full-length cDNA and the corresponding gene of the heat shock protein 90, Mt-Hsp90, were isolated and characterized in the plant parasitic nematode Meloidogyne artiellia. The full-length Mt-Hsp90 cDNA contained a 5' untranslated region (UTR) of 45 bp with the 22 bp trans-spliced leader SL1, an ORF of 2172 bp encoding a polypeptide of 723 amino acids and a 3' UTR of 191 bp. The deduced amino acid sequence of Mt-hsp90 showed high similarity with other known Hsp90s. Five conserved amino acid signatures indicated that Mt-hsp90 is a cytosolic member of the Hsp90 family. The gene consists of 10 exons and 9 introns, a more expanded gene structure compared to the corresponding Caenorhabditis elegans gene, daf-21. Mt-hsp90 gene was constitutively expressed at high levels in all developmental stages of M. artiellia. Egg masses and second stage juveniles (J2s) were exposed at 5 degrees and 30 degrees C for different periods of times in order to explore the impact of adverse temperature on Mt-hsp90 gene expression. Expression levels of Mt-hsp90 were examined by fluorescent real-time PCR. At 30 degrees C a burst of expression for Mt-hsp90 was observed in J2s after 2 h of heat shock treatment, then expression dropped with longer exposing times, although remaining still relatively high after 24 h. This temperature did not affect Mt-hsp90 gene expression in the egg masses. However, egg masses exposed at 5 degrees C showed a little but gradual increase in the mRNA level with time. By contrast, no significant changes in the Mt-hsp90 level were observed in J2s exposed to cold. These data show that egg masses and J2s exposed to cold and heat stresses have different expression profiles suggesting that Mt-Hsp90 may provide a link between environmental conditions and the life cycle of the nematode.

Insect thermal tolerance: what is the role of ontogeny, ageing and senescence?

Temperature has dramatic evolutionary fitness consequences and is therefore a major factor determining the geographic distribution and abundance of ectotherms. However, the role that age might have on insect thermal tolerance is often overlooked in studies of behaviour, ecology, physiology and evolutionary biology. Here, we review the evidence for ontogenetic and ageing effects on traits of high- and low-temperature tolerance in insects and show that these effects are typically pronounced for most taxa in which data are available. We therefore argue that basal thermal tolerance and acclimation responses (i.e. phenotypic plasticity) are strongly influenced by age and/or ontogeny and may confound studies of temperature responses if unaccounted for. We outline three alternative hypotheses which can be distinguished to propose why development affects thermal tolerance in insects. At present no studies have been undertaken to directly address these options. The implications of these age-related changes in thermal biology are discussed and, most significantly, suggest that the temperature tolerance of insects should be defined within the age-demographics of a particular population or species. Although we conclude that age is a source of variation that should be carefully controlled for in thermal biology, we also suggest that it can be used as a valuable tool for testing evolutionary theories of ageing and the cellular and genetic basis of thermal tolerance.

Impact of mild temperature hardening on thermotolerance, fecundity, and Hsp gene expression in Liriomyza huidobrensis

The pea leafminer, Liriomyza huidobrensis, is one of the most important economic insect pests around the world. Its population fluctuates greatly with seasonal change in China, and temperature was thought to be one of the important reasons. In attempt to further explore the impact of disadvantageous temperature on L. huidobrensis, 1-day-old adults were shocked at various temperatures (10, 25, 32, and 35 degrees C, respectively) for 4h, and the effects on thermotolerance, feeding, and fecundity were studied. Meanwhile the expression of five heat shock genes (hsp90, 70, 60, 40, and 20) was examined by real-time quantitative PCR. Our results showed that both 32 and 35 degrees C hardenings remarkably increased adult heat resistance, whereas cold tolerance was not improved accordingly. No cross resistance in response to cold and heat stresses was observed. Both adult feeding and fecundity were dramatically reduced, but no effect was observed on egg hatching, larval survival, pupal eclosion, or sex ratio. The results indicate that the deleterious effect on fecundity is the result of direct cessation of oviposition during the period of stress. Simultaneously, the mRNA levels of hsp70 and hsp20 significantly increased upon thermal hardening. Taken together, our results suggest that mild heat hardening improves thermotolerance of L. huidobrensis at the cost of impairment on fecundity, and the induced expression of hsp70 and hsp20 may play an important role in balancing the functional tradeoff.

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.

Shifts in the carbohydrate, polyol, and amino acid pools during rapid cold-hardening and diapause-associated cold-hardening in flesh flies (Sarcophaga crassipalpis): a metabolomic comparison

Flesh flies can enhance their cold hardiness by entering a photoperiod-induced pupal diapause or by a temperature-induced rapid cold-hardening process. To determine whether the same or different metabolites are involved in these two responses, derivatized polar extracts from flesh flies subjected to these treatments were examined using gas chromatography-mass spectrophotometry (GC-MS). This metabolomic approach demonstrated that levels of metabolites involved in glycolysis (glycerol, glucose, alanine, pyruvate) were elevated by both treatments. Metabolites elevated uniquely in response to rapid cold-hardening include glutamine, cystathionine, sorbitol, and urea while levels of beta-alanine, ornithine, trehalose, and mannose levels were reduced. Rapid cold-hardening also uniquely perturbed the urea cycle. In addition to the elevated metabolites shared with rapid cold-hardening, leucine concentrations were uniquely elevated during diapause while levels of a number of other amino acids were reduced. Pools of two aerobic metabolic intermediates, fumarate and citrate, were reduced during diapause, indicating a reduction of Krebs cycle activity. Principal component analysis demonstrated that rapid cold-hardening and diapause are metabolically distinct from their untreated, non-diapausing counterparts. We discuss the possible contribution of each altered metabolite in enhancing the overall cold hardiness of the organism, as well as the efficacy of GC-MS metabolomics for investigating insect physiological systems.

cDNA cloning of heat shock proteins and their expression in the two phases of the migratory locust

The high population density of insects is often a stress factor. Insects synthesize heat shock proteins (Hsps) in response to the impacts of stress through molecular chaperone activity. Locust solitary and gregarious phases occur at low and high population density, respectively. In this study, we compare the expression profiles of the Hsp genes in the two phases of the migratory locust in an attempt to examine the role of Hsps in adaptation to high density populations. The full length cDNAs of Hsp20.5, 20.6, 20.7, 40, 70 and Hsp90 of the migratory locust were cloned and sequenced. The expressional differentiation of the six Hsps in mRNA levels between solitary and gregarious locusts was observed. Results from real-time PCR indicate that the six Hsps are expressed throughout all developmental stages except in the early stage embryo. The expression levels of the six Hsps were significantly upregulated in gregarious locusts. The expressional variations among certain organs, such as the head, thorax and leg of fifth instar nymphs in gregarious locusts were also higher than those in solitary ones. These observations suggest that population density may be an important factor in determining Hsp expression in the locust.

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.

Supercooling ability is surprisingly invariable in eggs of the land snail Cantareus aspersus

From an ontogenetic point of view, invertebrate eggs are generally the most freezing intolerant stage of a species. Development state, water content and acclimation may affect their supercooling ability. In this study, we measured fresh mass, water content and temperature of crystallisation (T(c)) of eggs of the edible land snail Cantareus aspersus, depending on its form ("aspersa"vs. "maxima"), incubation temperature (20, 12 and 7 degrees C) and physiological age (as part of the complete development). We also tested their tolerance to freezing. Despite a high number of individual observations (n=759) and significant differences of fresh mass and water content between both subspecies, no effect of origin, incubation temperature or development state has been found in this study. T(c) remained constant whatever the condition, with an overall mean of -5.40+/-0.24 degrees C (mean+/-SD). We suggest that fresh mass is important, a high water content and a constantly wet surface confer to land snail eggs a poor ability to supercool. Moreover, the presence of ice nucleating agents at the egg surface (microorganisms present in the soil, calcium carbonate crystals of the egg shell) might induce freezing. Thus, considering the present results, to delay hatching by cryopreservation of eggs does not seem possible.

Thermoperiodic acclimations enhance cold hardiness of the eggs of the migratory locust

Treatment of thermoperiods that simulate the patterns of natural occurrence is most efficient in enhancing cold hardiness. To examine the effects of different thermoperiods on cold hardiness of eggs in the migratory locust, Locusta migratoria (L.), the survival rates, cryoprotectant levels and three hsps expressions in mid-stage eggs (7-day-old) were measured after the eggs were subjected to three different thermoperiod regimes, : short (2 day), long (10 day), and nature-mimicking thermoperiodic acclimation. The thermoperiodic acclimations resulted in the highest egg survival rates in both the short and the long period acclimation groups in comparison with the groups treated with constant temperatures. The egg survival of nature-mimicking thermoperiod groups was significantly higher than those of constant temperature groups for the same acclimation duration. The survival rate of eggs under single daily thermoperiod was higher than that of multiple daily thermoperiods. The concentration of cryoprotectants (myo-inositol, trehalose, mannitol and sorbitol) and the expression levels of hsp20.5, hsp70, and hsp90 all increased in thermoperiodic acclimation eggs.

Defensive components in insect eggs: are anthraquinones produced during egg development?

Eggs of several insect species are protected against natural enemies by noxious components. However, almost nothing is known about the fate of these defensive substances during egg development nor their site of biosynthesis. The eggs of several leaf beetle species of the taxon Galerucini contain components that are unusual in insects: 1,8-dihydroxylated anthraquinones and anthrones that deter predators such as ants and birds. These components, i.e., the anthrones dithranol and chrysarobin, and the anthraquinones chrysazin and chrysophanol, are not sequestered from host plants. We asked whether the amounts of these components in the overwintering eggs of Galeruca tanaceti change from deposition to larval hatching. Gas chromatography-mass spectroscopy (GC-MS) analyses of eggs revealed a significant decrease in total amounts of dithranol and chrysophanol from egg deposition in autumn to the next spring 5 months later. Thus, these results do not provide any hint of active anthraquinone biosynthesis within eggs. Instead, the anthrones and anthraquinones that must be incorporated by the female into the eggs seem to be degraded to some extent either by the embryo or endosymbionts. GC-MS analyses showed that parasitization of eggs had some effects on the quantities of anthrones and anthraquinones.