Physiological effect of mild thermal stress and its induction of gene expression in the common cutworm, Spodoptera litura

Cytoplasmic Hsp70s promote EcR transport into the nucleus by responding to various stimuli

Metamorphosis is one of the most important physiological processes in insects, which is coordinated by juvenile hormone (JH) and 20-hydroxyecdysone (20E). Ecdysone receptor (EcR) is a steroid receptor (SR), which usually presents in cytoplasm and transfers into nucleus after binding to 20E. Heat shock proteins (Hsps) are suggested to be important members of the SR complex. However, their role in nucleocytoplasmic shuttle of the EcR remains unclear. In the present study, we found that apoptozole (Hsp70 inhibitor) suppressed the larval molting by decreasing the expression of ecdysone signaling genes. Two cytoplasmic (Cy) Hsp70s (Hsp72 and Hsp73) interacted with both EcR and ultraspiracle (USP, the heterodimer partner of EcR). By immunohistochemistry experiments, we revealed that CyHsp70 co-localized with EcR in the cytoplasm, and that both apoptozole and interfering of CyHsp70 significantly inhibited the process of EcR entering the nucleus under 20E induction, while reducing the expression of ecdysone signaling genes. Interestingly, the nuclear localization of EcR was also promoted by two other stimuli, including JH and heat stress, and this promotion was inhibited by apoptozole. This implies that various stimuli can induce EcR entry into the nucleus, and that this process is mediated by CyHsp70. Curiously, neither JH nor heat stress activated the ecdysone signaling genes; instead, they have a significant inhibitory effect on them. Taken together, it seems that Cytoplasmic Hsp70s promote EcR transport into the nucleus by responding to various stimuli, and that the biological effects of various stimuli passing through the EcR are different. Thus, our data provide a new viewpoint to understand the mechanism of nucleocytoplasmic shuttle of EcR.

Fate and effects of microplastics in combination with pharmaceuticals and endocrine disruptors in freshwaters: Insights from a microcosm experiment

Microplastic contamination of freshwater ecosystems has become an increasing environmental concern. To advance the hazard assessment of microplastics, we conducted a microcosm experiment in which we exposed a simplified aquatic ecosystem consisting of moss and caddisflies to microplastics (polyethylene, polystyrene and polypropylene) and pharmaceuticals and personal care products (1H-benzotriazole, bisphenol A, caffeine, gemfibrozil, ketoprofen, methylparaben, estriol, diphenhydramine, tris (1-chloro-2-propyl) phosphate) over the course of 60 days. We monitored the flux of microplastics within the microcosm, as well as the metabolic and total protein variation of organisms. This study offers evidence highlighting the capacity of moss to act as a sink for free-floating microplastics in freshwater environments. Moss is also shown to serve as a source and pathway for microplastic particles to enter aquatic food webs via caddisflies feeding off of the moss. Although most ingested microparticles were eliminated between caddisflies life stages, a small fraction of microplastics was transferred from aquatic to terrestrial ecosystem by emergence. While moss exhibited a mild response to microplastic stress, caddisflies ingesting microplastics showed stress comparable to that caused by exposure to pharmaceuticals. The molecular responses that the stressors triggered were tentatively identified and related to phenotypic responses, such as the delayed development manifested through the delayed emergence of caddisflies exposed to stress. Overall, our study provides valuable insights into the adverse effects of microplastics on aquatic species, compares the impacts of microplastics on freshwater biota to those of pharmaceuticals and endocrine disrupting compounds, and demonstrates the role aquatic organisms have in redistributing microplastics between aquatic and terrestrial ecosystems.

Review of molecular and biochemical responses during stress induced stimulation and hormesis in insects

The biphasic hormetic response to stress, defined by low-dose stimulation and high-dose inhibition is frequently observed in insects. Various molecular and biochemical responses associated with hormesis in insects have been reported in many studies, but no synthesis of all these findings has been undertaken. We conducted a systematic literature review, analyzing papers demonstrating phenotypic stimulatory effect(s) following exposure to stress where molecular or biochemical response(s) were also examined. Responses observed included stimulation of reproduction, survival and longevity, growth and development, and tolerance to temperature, chemical, or starvation and desiccation, in response to stressors including pesticides, oxidative stress, temperature, crowding and starvation, and radiation. Phenotypic stimulation ranged from <25% increased above controls to >100%. Reproductive stimulation was frequently <25% increased above controls, while stimulated temperature tolerance was frequently >100% increased. Molecular and biochemical responses had obvious direct connections to phenotypic responses in many cases, although not in all instances. Increased expression of heat shock proteins occurred in association with stimulated temperature tolerance, and increased expression of detoxification genes with stimulated pesticide or chemical tolerance, but also stimulated reproduction. Changes in the expression or activity of antioxidants were frequently associated with stimulation of longevity and reproduction. Stress induced changes in vitellogenin and juvenile hormone and genes in the IIS/TOR signalling pathway - which are directly responsible for regulating growth, development, and reproduction - were also reported. Our analysis showed that coordination of expression of genes or proteins associated with protection from oxidative stress and DNA and protein damage is important in the hormetic responses of insects.

Genes associated with hot defensive bee ball in the Japanese honeybee, Apis cerana japonica

Background

The Japanese honeybee, Apis cerana japonica, shows a specific defensive behavior, known as a “hot defensive bee ball,” used against the giant hornet, Vespa mandarinia. Hundreds of honeybee workers surround a hornet and make a “bee ball” during this behavior. They maintain the ball for around 30 min, and its core temperature can reach 46. Although various studies have been conducted on the characteristics of this behavior, its molecular mechanism has yet to be elucidated. Here, we performed a comprehensive transcriptomic analysis to detect candidate genes related to balling behavior.

Results

The expression levels of differentially expressed genes (DEGs) in the brain, flight muscle, and fat body were evaluated during ball formation and incubation at 46 °C. The DEGs detected during ball formation, but not in response to heat, were considered important for ball formation. The expression of genes related to rhodopsin signaling were increased in all tissues during ball formation. DEGs detected in one or two tissues during ball formation were also identified.

Conclusions

Given that rhodopsin is involved in temperature sensing in Drosophila, the rhodopsin-related DEGs in A. cerana japonica may be involved in temperature sensing specifically during ball formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-01989-9.

Constraints and Opportunities for the Evolution of Metamorphic Organisms in a Changing Climate

We argue that developmental hormones facilitate the evolution of novel phenotypic innovations and timing of life history events by genetic accommodation. Within an individual’s life cycle, metamorphic hormones respond readily to environmental conditions and alter adult phenotypes. Across generations, the many effects of hormones can bias and at times constrain the evolution of traits during metamorphosis; yet, hormonal systems can overcome constraints through shifts in timing of, and acquisition of tissue specific responses to, endocrine regulation. Because of these actions of hormones, metamorphic hormones can shape the evolution of metamorphic organisms. We present a model called a developmental goblet, which provides a visual representation of how metamorphic organisms might evolve. In addition, because developmental hormones often respond to environmental changes, we discuss how endocrine regulation of postembryonic development may impact how organisms evolve in response to climate change. Thus, we propose that developmental hormones may provide a mechanistic link between climate change and organismal adaptation.

Expression of 20-hydroxyecdysone-related genes during gonadal development of Teleogryllus emma (Orthoptera: Gryllidae)

Insect gonads develop under endocrine signals. In this study, we assessed the characters of partial complementary DNAs encoding the Teleogryllus emma orthologs of 20-hydroxyecdysone (20E)-related genes (RXR, E75, HR3, Hsc70, and Hsp90) and analyzed their expression patterns in both nymph and adult crickets. 20E treatment suppressed expression of TeEcR, TeRXR, TeE75, TeHR3, TeHsc70, and TeHsp90. Temporal expression analysis demonstrated that TeERR and 20E-related genes were expressed in four stages of gonadal development from the fourth-instar nymph stage to the adult stage. The expression pattern of these genes differed in testicular and ovarian development. TeRXR, HR3, TeHsc70, and TeHsp90 were irregularly expressed in gonads of the same developmental stages, while mRNAs encoding TeERR, TeEcR, and TeE75 accumulated in higher levels in ovaries than in testes. RNA interference (RNAi) of TeEcR expression led to decrease of the expression levels of TeEcR, TeRXR, TeHR3, and TeHsc70, while it enhanced TeE75 and TeHsp90 expressions. These results demonstrate that the TeERR and 20E-related genes help regulate gonadal development, while TeEcR appears to inhibit TeE75 expression, TeE75 inhibits HR3 expression. Hsc70 indirectly regulated the expression of the primary and secondary response genes E74A, E75B, and HR3. Hsp90 regulated Usp expression with no direct regulatory relationship with EcR.

Larvae Crowding Increases Development Rate, Improves Disease Resistance, and Induces Expression of Antioxidant Enzymes and Heat Shock Proteins in Mythimna separata (Lepidoptera: Noetuidae)

High population density (crowding) becomes a stress factor in insects. The oriental armyworm, Mythimna separata (Walker), displays gregarious and solitary phases at high and low population densities, respectively. In this study, we compared life history, disease resistance, and induction of antioxidant enzymes and heat shock protein (HSPs) in two phases of M. separata larvae. Results showed that gregarious larvae had a faster growth rate and lower pupal weight compared to solitary larvae. Furthermore, gregarious individuals exhibited higher survival rates than solitary individuals after Beauveria bassiana infection. The gregarious larvae had higher malondialdehyde content compared to solitary ones, but no differences in total antioxidant capacity were observed between the two larval phases before or after infection. Superoxide dismutase and glutathione peroxidase activities were significantly lower in gregarious M. separata larvae than solitary individuals before infection, but no difference was detected in two phases after infection. However, peroxidase and catalase activities in the two phases showed no difference either before or after infection. Hsp19.8 and Hsp90 expression in gregarious larvae were up-regulated when compared to solitary individuals before or after infection. CuZnSOD expression was not different between the two phases before infection, but it was up-regulated in gregarious ones compared to solitary ones after infection. However, expression of other stress-related genes in gregarious larvae was either repressed or unchanged when compared to solitary individuals before or after infection. Thus, larval crowding changed life history, improved disease resistance of M. separata larvae, and induced variable response of antioxidant enzymes and HSPs to fungal infection.

Comprehensive analysis of differentially expressed proteins in the male and female Bombyx mori larval instars exposed to thermal stress

Gender sensitivity to ambient heat, despite well known in insect species, how it manifests during young and late larval instars of Bombyx mori is still unclear. To uncover this cryptic feature, different instars male and female larvae were subjected to varied thermal stress separately and sex-stage specific expression of proteins was investigated. Interestingly, heat shock proteins (HSPs) 90 and 70 were expressed differently in all the instars and also between male and female larvae as confirmed by immunoblot assay. Besides up- and downregulation of few HSPs and other normal proteins, discreet expression of protein was noticed in the two-dimensional gel electrophoresis of male than female larvae which were identified as HSP70 by mass spectrometry. Furthermore, quantitative polymerase chain reaction results show 3.98- and 4.86-fold higher levels of Bmhsp70 and Bmhsp90 transcripts in male and female larvae, respectively, as a response to 40°C heat shock (HS) treatment. Conversely, in spite of the massive production of HSPs due to HS at 45°C, all the larvae were found dead, which is a strong proof of concept for autophagy. Comparatively, female larvae HS at 40°C succeed to spin cocoons with increased weight and silk contents than non-HS larvae. Comprehensively, in the present study, we have noticed a strong correlation for the first time that Bmhsp90 and Bmhsp70 genes expressions due to thermal stress are not only sex specific but also explicit preferential and coordinated action on survivability and biosynthetic potential of the silkworm, B. mori larvae during different instars.

Characterization and expression analysis of genes encoding three small heat shock proteins in the oriental armyworm, Mythimna separata (Walker)

Small heat shock proteins (sHsps) function in the response of insects to abiotic stress; however, their role in response to biotic stress has been under-investigated. Mythimna separata, the oriental armyworm, is polyphenetic and exhibits gregarious and solitary phases in response to high and low population density, respectively. In this study, three genes were identified encoding sHsps, namely MsHsp19.7, MsHsp19.8 and MsHsp21.4, and expression levels in solitary and gregarious M. separata were compared. The deduced protein sequences of the three MsHsps had molecular weights of 19.7, 19.8 and 21.4 kDa, respectively, and contained a conserved α-crystalline domain. Real-time PCR analyses revealed that the three sHsps were transcribed in all developmental stages and were dramatically up-regulated at the 6^th larval stage in gregarious individuals. Expression of the three MsHsps was variable in different tissues of 6^th instar larvae, but exhibited consistent up- and down-regulation in the hindgut and Malpighian tubules of gregarious individuals, respectively. In addition, MsHsp19.7 and MsHsp19.8 were significantly induced when solitary forms were subjected to crowding for 36 h, but all three MsHsps were down-regulated when gregarious forms were isolated. Our findings suggest that population density functions as a stress factor and impacts MsHsps expression in M. separata.

Combined thermal and insecticidal stresses on the generalist predator Macrolophus pygmaeus

Ecotoxicological risk assessments of pesticides on non-target arthropods are often carried out under constant and optimal temperature regimes. However, living organisms rarely experience these conditions in real field situations. Understanding the impact of pesticides on non-target beneficial arthropods under temperature stresses is especially important in terms of global warming. We assessed the lethal and sublethal effects of four modern insecticides (chlorantraniliprole, cyantraniliprole, spinetoram, spinosad), on the generalist predator Macrolophus pygmaeus (Hemiptera: Miridae) under a range of temperatures (from 10 to 40°C) frequently experienced in a real field scenario. A reduction coefficient (E_x) was calculated by summarizing the mortality and predator reproductive capacity and, the chemicals were classified according to the International Organization for Biological Control (IOBC) toxicity classes. The insecticides showed a marked synergistic effect with temperature, as the predator mortality and reproductive outputs were significantly correlated with increasing temperatures. Spinosyns interacted significantly with temperature causing the highest mortality and lowest fertility rates. Anthranilic diamides showed a safer ecotoxicological profile compared to spinosyns, with cyantraniliprole being more harmful than chlorantraniliprole. These results suggest that temperature should be taken into account in pesticide ecotoxicology studies within the framework of integrated pest management and the recent climate changes.

Transcriptomic analysis reveals Apis mellifera adaptations to high temperature and high humidity

Temperature and humidity are the most important factors affecting the growth, reproduction, and survival of bees. Apis mellifera are important pollinating bees that are widely used in agricultural systems. However, the higher temperatures and humidity in greenhouses are not conducive to the survival of bees. Although previous research has revealed the behavioral responses and physiological mechanisms of honeybees to adapt to high temperature and humidity, there are few data on the exact molecular mechanisms involved. In our study, we investigated gene expression in A. mellifera under different temperature and humidity treatments, using transcriptomic analysis to identify differentially expressed genes (DEGs) and relevant biological processes. Based on the transcriptomic results, we selected several genes with significant differences in expression, and detected the expression patterns of these genes at different temperatures or humidity or different treatment times by q-RT PCR. In the high temperature treatments, 434 DEGs were identified; in the high humidity treatments, 86 DEGs were identified; in the combined high temperature and humidity treatments, 266 DEGs were identified. Analysis results showed that DEGs were enriched in pathways related to amino acid and fatty acid biosynthesis and metabolism under each treatment. In addition, heat shock proteins, zinc finger proteins, serine/threonine-protein kinases, and antioxidase were differentially expressed between the different treatments. The results of the q-RT PCR showed that the expression levels of these genes increased with increasing temperature and over treatment time. Our findings provide a general expression profile of the adaptive expression of heat-resistance genes responding to high temperature and high humidity in A. mellifera, including the expression patterns of several DEGs. Our data provide a basis for future research on the mechanisms underlying the adaptation of insects to high temperature and humidity.

Transcriptomic analysis of differentially expressed genes in the oriental armyworm Mythimna separata Walker at different temperatures

The oriental armyworm Mythimna separata Walker is a serious migratory and polyphagous pest that damages major crops and some pastures from the family Gramineae. Temperature is a crucial abiotic factor that affects its survival, development and reproduction, but the thermal responses of this moth at the molecular level are largely unknown. In this research, we sequenced the transcriptomes of oriental armyworms that were reared at three temperatures (20 °C, 25 °C and 30 °C) using an Illumina high-throughput RNA-sequencing (RNA-seq) method. We obtained 54.0 Gb of clean reads and 113,396 transcripts. From a total of 46,681 unigenes identified, 22,911 were annotated to the non-redundant (NR) database. We identified 333 downregulated and 1588 upregulated genes in 20 °C versus 25 °C, and 1096 downregulated and 875 upregulated genes at 30 °C versus 25 °C by differential expression of genes (DEGs). GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses revealed several functional terms related to carbohydrate metabolism, energy metabolism, and xenobiotics metabolism. DEGs involved in glycolysis, the citrate cycle, oxidative phosphorylation, and the composition of myofilaments were significantly downregulated, while most heat shock protein genes (HSPs) and genes in the ubiquitin-mediated proteasome pathway were upregulated at 30 °C. Many cytochrome P450 monooxygenase genes (CYPs) in clan 3 were upregulated at 20 °C, while two genes involved in ecdysteroid biosynthesis, CYP302A1 and CYP315A1, were upregulated at 30 °C. These data may improve the understanding of the complex molecular mechanisms involved in the thermal responses of M. separata.

Effect of short-term high-temperature exposure on the life history parameters of Ophraella communa

Extreme heat in summer is frequent in parts of China, and this likely affects the fitness of the beetle Ophraella communa, a biological control agent of invasive common ragweed. Here, we assessed the life history parameters of O. communa when its different developmental stages were exposed to high temperatures (40, 42 and 44 °C, with 28 °C as a control) for 3 h each day for 3, 5, 5, and 5 days, respectively (by stage). The larval stage was the most sensitive stage, with the lowest survival rate under heat stress. Egg and pupal survival significantly decreased only at 44 °C, and these two stages showed relative heat tolerance, while the adult stage was the most tolerant stage, with the highest survival rates. High temperatures showed positive effects on the female proportion, but there was no stage-specific response. Treated adults showed the highest fecundity under heat stress and a similar adult lifespan to that in the control. High temperatures decreased the F₁ egg hatching rate, but the differences among stages were not significant. Negative carry-over effects of heat stress on subsequent stages and progenies’ survival were also observed. Overall, heat effects depend on the temperature and life stage, and the adult stage was the most tolerant stage. Ophraella communa possesses a degree of heat tolerance that allows it to survive on hot days in summer.

Increased survival of honeybees in the laboratory after simultaneous exposure to low doses of pesticides and bacteria

Recent studies of honeybees and bumblebees have examined combinatory effects of different stressors, as insect pollinators are naturally exposed to multiple stressors. At the same time the potential influences of simultaneously occurring agricultural agents on insect pollinator health remain largely unknown. Due to different farming methods, and the drift of applied agents and manure, pollinators are most probably exposed to insecticides but also bacteria from organic fertilizers at the same time. We orally exposed honeybee workers to sub-lethal doses of the insecticide thiacloprid and two strains of the bacterium Enterococcus faecalis, which can occur in manure from farming animals. Our results show that under laboratory conditions the bees simultaneously exposed to the a bacterium and the pesticide thiacloprid thiacloprid had significant higher survival rates 11 days post exposure than the controls, which surprisingly showed the lowest survival. Bees that were exposed to diet containing thiacloprid showed decreased food intake. General antibacterial activity is increased by the insecticide and the bacteria, resulting in a higher immune response observed in treated individuals compared to control individuals. We thus propose that caloric restriction through behavioural and physiological adaptations may have mediated an improved survival and stress resistance in our tests. However, the decreased food consumption could in long-term also result in possible negative effects at colony level. Our study does not show an additive negative impact of sub-lethal insecticide and bacteria doses, when tested under laboratory conditions. In contrast, we report seemingly beneficial effects of simultaneous exposure of bees to agricultural agents, which might demonstrate a surprising biological capacity for coping with stressors, possibly through hormetic regulation.

Ultraviolet filters and heat shock proteins: effects in Chironomus riparius by benzophenone-3 and 4-methylbenzylidene camphor

Benzophenone-3 (BP3) and 4-methylbenzylidene camphor (4MBC) are common ultraviolet filters (UV filters), compounds considered as emergent contaminants, used in different products like plastics and personal care products. The levels of these compounds are rising in the wild, but the effects they have on invertebrates are poorly understood. Chironomus riparius is a benthic insect widely used in toxicology, and several studies have been previously performed in our laboratory to determine the effects these compounds have on this organism at the molecular level. We have shown that UV filters can alter the mRNA levels of heat shock protein 70 (Hsp70), one of the most studied heat shock proteins. Although these proteins are crucial for the survival of organisms, little data is available on the effects these emergent contaminants have on them, especially in invertebrates. Here, we analyzed the transcriptional activity of 12 genes covering the different groups of heat shock protein [Hsp10, Hsp17, Hsp21, Hsp22, Hsp23, Hsp24, Hsp27, Hsp34, Hsp40, Hsp60, Hsc70 (3), and Hsc70 (4)] in response to 0.1 and 1 mg/L concentrations of BP3 and 4MBC at 8 and 24 h. The results showed that some small Hsp (sHsp) genes were altered by these compounds, while the genes of proteins present in mitochondria, Hsp10 and Hsp60, did not change. sHsps are also involved in developmental processes, so the observed variations could be due to the endocrine disruption activity described for these compounds rather than to a stress response.

Heat stress hardening of oriental armyworms is induced by a transient elevation of reactive oxygen species during sublethal stress

Pre-exposure to mild heat stress enhances the thermotolerance of insects. Stress hardening is a beneficial physiological plasticity, but the mechanism underlying it remains elusive. Here we report that reactive oxygen species (ROS) concentrations were quickly and transiently elevated in the armyworms, Mythimna separata, by exposing them to 40°C, but not other tested temperatures. Larvae exposed to 40°C had subsequently elevated antioxidant activity and the highest survival of all tested heating conditions. The elevation of ROS after lethal heating at 44°C for 1 h was approximately twofold compared to heating at 40°C. Injection of an optimal amount of hydrogen peroxide (H₂ O₂ ) similarly caused sequential elevation of ROS and antioxidant activity in the test larval hemolymph, which led to significantly enhanced survival after lethal heat stress. The H₂ O₂ -induced thermotolerance was abolished by coinjection of potent antioxidants such as ascorbic acid or N-acetylcysteine. Both preheating at 40°C and H₂ O₂ injection enhanced expression of genes encoding superoxide dismutase 1, catalase, and heat shock protein 70 in the fat body of test larvae, indicating the adequate heat stress induced a transient elevation of ROS, followed by upregulation of antioxidant activity. We infer that thermal stress hardening is induced by a small timely ROS elevation that triggers a reduction-oxidation signaling mechanism.

Thermotolerance and Heat-Shock Protein Gene Expression Patterns in Bemisia tabaci (Hemiptera: Aleyrodidae) Mediterranean in Relation to Developmental Stage

Temperature plays an important role in the growth, development, and geographic distribution of insects. There is convincing evidence that heat-shock proteins (HSPs) play important roles in helping organisms adapt to thermal stress. To better understand the physiological and ecological influence of thermal stress on the different development stages of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Mediterranean species (MED), nymphs and adults were shocked with temperatures of 35, 38, and 41℃ for 1 and 2 h, respectively, and the survival rate, fecundity, and developmental duration were investigated in the laboratory. The expression levels of the hsp40, hsp70, and hsp90 genes were assessed using real-time PCR. The results indicate that the survival rates of the nymphs and adults decreased with increased temperature. A 2-h heat shock at 41℃ induced a significant reduction in fecundity in adults and an increase in developmental duration in young nymphs. Hsp90 showed higher temperature responses to thermal stress than hsp40 or hsp70. The expression levels of the hsps in the adults were significantly down-regulated by a 2-h heat shock at 41℃ compared with that by a 1-h treatment. A significant decrease in the expression levels of the hsps also occurred in the adults when the temperature increased from 38 to 41℃ for the 2-h treatment, whereas no significant decrease occurred in the nymphs. Compared with previous studies, we provide some evidence indicating that MED has the potential to adapt to a wider temperature range than the Middle East-Asia Minor 1 species.

Thermotolerance, oxidative stress, apoptosis, heat-shock proteins and damages to reproductive cells of insecticide-susceptible and -resistant strains of the diamondback moth Plutella xylostella

In this study, we investigated thermotolerance, several physiological responses and damage to reproductive cells in chlorpyrifos-resistant (Rc) and -susceptible (Sm) strains of the diamondback moth, Plutella xylostella subjected to heat stress. The chlorpyrifos resistance of these strains was mediated by a modified acetylcholinesterase encoded by an allele, ace1R, of the ace1 gene. Adults of the Rc strain were less heat resistant than those of the Sm strain; they also had lower levels of enzymatic activity against oxidative damage, higher reactive oxygen species contents, weaker upregulation of two heat shock protein (hsp) genes (hsp69s and hsp20), and stronger upregulation of two apoptotic genes (caspase-7 and -9). The damage to sperm and ovary cells was greater in Rc adults than in Sm adults and was temperature sensitive. The lower fitness of the resistant strain, compared with the susceptible strain, is probably due to higher levels of oxidative stress and apoptosis, which also have deleterious effects on several life history traits. The greater injury observed in conditions of heat stress may be due to both the stronger upregulation of caspase genes and weaker upregulation of hsp genes in resistant than in susceptible individuals.

Effects of high temperature on life history traits and heat shock protein expression in chlorpyrifos-resistant Laodelphax striatella

The resistance of the small brown planthopper (SBPH), Laodelphax striatella, to insecticides has been widely found in China, and has posed serious problems to efforts to control the pest. To determine the costs and benefits of resistance, the life tables of chlorpyrifos-resistant and -susceptible strains were constructed at 24 and 30°C. The results showed the resistant SBPH (YN-CPF) had lower fitness at 24°C, but slightly higher fitness at 30°C compared to the susceptible SBPH. Transcriptomic analysis showed there are five heat shock protein genes changed their expression, and the up-regulated genes are LsHsc70-1 and LsHsc70-2. The deduced amino acid sequences of LsHsc70-1 and LsHsc70-2 include three heat shock protein 70 (HSP70) family signatures, but LsHSC70-1 has the conserved HSP70 carboxyl terminal region of the "EEVD" motif, while LsHSC70-2 has the endoplasmic reticulum (ER) retention signal of the "KDEL" motif. The phylogenetic tree further identified LsHsc70-1 has closer evolutionary distances to cytoplasmic/nuclear HSP70s from human and Drosophila melanogaster, while LsHsc70-2 has closer evolutionary distances to HSP70s localized to ER. After treatment at 30-44°C, the expression of LsHsc70-1 and LsHsc70-2 was slightly increased in YN-CPF. These results suggested that LsHsc70-1 and LsHsc70-2 are members of Hsc70 family, localized to the cytosol/nucleus and ER, respectively. The up-regulated expression of these genes may protect the chlorpyrifos-resistant pest against damage under high temperatures, increasing its relative fitness, but the lower relative fitness of this population under optimal temperature may be the trade-off.

Transcription of four Rhopalosiphum padi (L.) heat shock protein genes and their responses to heat stress and insecticide exposure

The bird cherry-oat aphid, Rhopalosiphum padi (L.), a worldwide destructive pest, is more heat tolerant than other wheat aphids, and it has developed resistance to different insecticides. Heat shock proteins (HSPs) play an important role in coping with environmental stresses. To investigate Hsp transcriptional responses to heat and insecticide stress, four full-length Hsp genes from R. padi (RpHsp60, RpHsc70, RpHsp70-1, and RpHsp70-2) were cloned. Four RpHsps were expressed during all R. padi developmental stages, but at varying levels. The mRNA levels of RpHsps were increased under thermal stress and reached maximal induction at a lower temperature (36°C) in the alate morph than in the apterous morph (37°C or 38°C). RpHsp expressions under heat stress suggest that RpHsp70-1 and RpHsp70-2 are inducible in both apterous and alate morphs, RpHsc70 is only heat-inducible in apterous morph, and RpHsp60 exhibits poor sensitivity to heat stress. The pretreatment at 37°C significantly increase both the survival rate and the RpHsps expression level of R. padi at subsequent lethal temperature. Under exposure to two sublethal concentrations (LC₁₀ and LC₃₀) of beta-cypermethrin, both RpHsp70-1 and RpHsp70-2 expressions were induced and reached a maximum 24h after exposure. In contrast, expression of RpHsp60 was not induced by either sublethal concentration of beta-cypermethrin. Moreover, the responses of RpHsp70-1 and RpHsp70-2 to heat shock were more sensitive than those to beta-cypermethrin. These results suggest that induction of RpHsp expression is related to thermal tolerance, and that RpHsp70-1 and RpHsp70-2 are the primary genes involved in the response to both heat and pesticide stress.

Demographic comparison and population projection of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) reared on sugarcane at different temperatures

Understanding how temperature affects fitness is important for conservation and pest management, especially in the era of global climate change. Rhynchophorus ferrugineus (Oliver) (Coleoptera: Curculionidae) is a worldwide pest of many economically important crops. Although much is known about this pest’s life cycle, its adaptability to different temperatures is not fully understood. Here, we used age- and stage-specific life tables to investigate the effects of temperature on fitness-related traits and demographic parameters of R. ferrugineus under eight constant temperature regimens in the laboratory. The growth potential of these populations was also evaluated. The greatest longevity for males and females was 158.0 d at 24 °C and 144.5 d at 21 °C, respectively, but mean total fecundity was the highest at 27 °C. The intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R₀) increased initially at low temperatures and then decreased. All metrics reached a maximum at 27 °C and a minimum at 36 °C. Mean generation times (T ) decreased across the temperature range with a minimum at 36 °C. Our results indicate that the optimum temperature for growth of R. ferrugineus was approximately 27 °C. Our work will be of value for developing strategies for control management of this pest species.

Dynamics and regulation of glycolysis-tricarboxylic acid metabolism in the midgut of Spodoptera litura during metamorphosis

Significant changes usually take place in the internal metabolism of insects during metamorphosis. The glycolysis-tricarboxylic acid (glycolysis-TCA) pathway is important for energy metabolism. To elucidate its dynamics, the mRNA levels of genes involved in this pathway were examined in the midgut of Spodoptera litura during metamorphosis, and the pyruvate content was quantified. The expression patterns of these genes in response to starvation were examined, and the interaction between protein phosphatase 1 (PP1) and phosphofructokinase (PFK) was studied. The results revealed that the expression or activities of most glycolytic enzymes was down-regulated in prepupae and then recovered in some degree in pupae, and all TCA-related genes were remarkably suppressed in both the prepupae and pupae. Pyruvate was enriched in the pupal midgut. Taken together, these results suggest that insects decrease both glycolysis and TCA in prepupae to save energy and then up-regulate glycolysis but down-regulate TCA in pupae to increase the supply of intermediates for construction of new organs. The expression of all these genes were down-regulated by starvation, indicating that non-feeding during metamorphosis may be a regulator of glycolysis-TCA pathway in the midgut. Importantly, interaction between PP1 and PFK was identified and is suggested to be involved in the regulation of glycolysis.

Cloning and differential expression of five heat shock protein genes associated with thermal stress and development in the polyphagous predatory mite Neoseiulus cucumeris (Acari: Phytoseiidae)

In order to explore the role of heat shock proteins (Hsps) during thermal stress and development in the predatory mite Neoseiulus cucumeris (Oudemans), we cloned and characterized five full-length Hsp genes. We investigated the expression levels of these genes by quantitative real-time PCR. The five genes characterized here were NcHsp90, NcHsp75, NcHsp70, NcHsp60, and NcHsp40. These Hsps showed high sequence conservation and had greatest identity with heat shock proteins of Metaseiulus occidentalis and other mite and insect species. All five NcHsp genes showed changes in their levels of expression during development. Higher levels of expression were observed in adult females than in adult males, but there were no significant changes between pre-oviposition and post-oviposition stages in the females. NcHsp90, NcHsp75, and NcHsp70 expression levels were up-regulated after a heat shock, and the increases in NcHsp75 and NcHsp70 expression levels were maintained for at least 3 h. Up-regulation of NcHsp60 and NcHsp40 was not detected after 1 h at a high temperature (35-45 °C); however, a significant down-regulation was observed after 3 h heat exposure at 35 °C and 3 h recovery at 25 °C. Cold shock treatment (-5 to 15 °C) for 1 h did not acute elicit changes in the expression levels of any of the genes. At 5 °C, the expression levels of NcHsp90 significantly increased after 6 or 24 h exposure compared to the levels after 1 h exposure. Thus, expression of Hsp genes in N. cucumeris reflected developmental changes, sexual difference, and variable induced response to thermal stress. Increased expression of Hsps might protect N. cucumeris individuals under extreme temperature conditions. Therefore, it may be possible to enhance the thermal tolerance of commercially available N. cucumeris using temperature acclimation. Treatment at 35 °C should be suitable for such acclimation.

Comparative proteomic analysis of Bactrocera dorsalis (Hendel) in response to thermal stress

Temperature is one of the most important environmental variables affecting growth, reproduction and distribution of insects. The rise of comparative proteomics provides a powerful tool to explore the response in proteins to thermal stress. As an important worldwide pest, the oriental fruit fly Bactrocera dorsalis causes severe economic losses to crops. To understand the response of B. dorsalis to thermal stress, we performed a comparative proteome analysis of this insect after exposure to extreme low and high temperatures using two-dimensional electrophoresis. Among the separated proteins, 51 diverse protein spots were present differently in response to extreme temperatures. Using tandem mass spectrometry sequencing analysis 39 proteins were successfully identified, which included 13 oxidoreductases, 10 binding proteins, 5 transferases, and 2 each of lyases, isomerases, ligases, and developmental proteins. Subsequently, the expression of these protein transcripts was studied by RT-qPCR to validate the proteomic results. In conclusion, this study provides a first look into the thermal stress response of B. dorsalis at the protein level, and thus it paves the way for further functional studies in the physiological mechanism related to thermal stress.