A single hot event stimulates adult performance but reduces egg survival in the oriental fruit moth, Grapholitha molesta

Experimental evolution reveals that males evolving within warmer thermal regimes improve reproductive performance under heatwave conditions in a model insect

Climate change is increasing mean temperatures, and intensifying heatwaves. Natural populations may respond to stress through shorter-term acclimation via plasticity and/or longer-term inter-generational evolution. However, if the pace and/or extent of thermal change is too great, local extinctions occur; one potential cause in ectotherms is identified to be the heat-liability of male reproductive biology. Recent data from several species, including the beetle Tribolium castaneum, confirmed that male reproductive biology is vulnerable to heatwaves, which may constrain populations. However, such reproductive-damage may be overestimated, if there is potential to adapt to elevated mean temperatures associated with climate change via evolution and/or acclimation. Here, we tested this to evaluate whether pre-exposures could improve heatwave tolerance (adaptation or acclimation), by experimentally evolving Tribolium castaneum populations to divergent thermal regimes (30 °C vs. 38 °C). Findings across assays revealed that relative to 30 °C-regime males, males from the 38 °C regime, maintained constantly at 8 °C warmer for 25 generations, displayed an increase; (i) in post heatwave (42 °C) reproductive fitness by 55%, (ii) survival by 33%, and (iii) 32% larger testes volumes. Unexpectedly, in the acclimation assay, warm-adapted males' post-heatwave survival and reproduction were best if they experienced cool developmental acclimation beforehand, suggesting a cost to adapting to 38 °C. These results help progress knowledge of the potential for survival and reproduction to adapt to climate change; trait specific adaptation to divergent thermal regimes can occur over relatively few generations, but this capacity depended on the interaction of evolutionary and thermal acclimatory processes.

Warm and thermally variable incubation conditions reduce embryonic performance and carry over to influence hatchling tradeoffs

Animals' thermal sensitivities have long been characterized by thermal performance curves (TPCs) or reaction norms, and TPCs may predict animals' responses to climate change. Typically, TPCs are parameterized by measuring performance at a range of constant temperatures. Yet, animals encounter a range of thermal environments, and temperature variability is an aspect of climate change that may affect animals more than gradual warming. Daily temperature variability is particularly important for eggs in most taxa because they are highly sensitive to temperature and cannot behaviorally avoid stressful temperatures. Thus, the legacy of thermal conditions experienced during incubation may carryover to subsequent life stages. Here, I factorially manipulated mean temperature (20, 25, or 30 °C) and daily temperature range (DTR; ±0, 5, or 10 °C) during incubation for eggs of the variable field cricket (Gryllus lineaticeps) to integrate the role of DTR into the established paradigm of TPCs. Low DTR (±5 °C) was not generally costly, and it even improved hatchling starvation resistance (sensu hormesis). However, high DTR (±10 °C) reduced and delayed hatching at a warm mean temperature (30 °C). The effects of high DTR carried over to accelerate hatchling development at an expense to hatchling starvation resistance-therefore, thermal conditions during incubation can shape tradeoffs among important traits related to life history and stress tolerance later in life. In sum, animals may exhibit complex responses to their increasingly warmer, more thermally variable environments.

How Climate Warming Influences the Phenology of Grapholita molesta (Busck, 1916) (Lepidoptera: Tortricidae) in China: Insight from Long-Term Historical Data

Grapholita molesta (Busck, 1916), a significant pest affecting various fruits such as pears, apples, peaches, etc., is highly adaptable to changing temperatures. However, the phenological response mechanism of this pest to climate warming remains unclear. To address this issue, we collected population dynamics data of G. molesta in China over the years along with corresponding climate data. We analyzed five phenological indexes: the first, end, and peak occurrence dates of contemporary adults as well as the first and peak occurrence dates of overwintering adults in China. Results revealed an upward trend in the annual average temperature and average temperature of the four seasons in regions infested by G. molesta in eastern, northeastern, northwestern, northern, and southwestern China from 1980 to 2020. Notably, the population peak date of overwintering adults in northeastern and eastern China significantly advanced along with the first occurrence date and the population peak date of overwintering adults in northern China. Additionally, the population peak date of contemporary adults in northwestern China significantly advanced. However, the end occurrence date of contemporary adults in northern China was significantly delayed, as was the first occurrence date of overwintering adults in northwestern China. Furthermore, our study demonstrated spatial heterogeneity in the phenological response of G. molesta to climate warming across China. This study elucidates the phenological response of G. molesta to climate warming, offering valuable insights for predicting future pest infestations and informing adaptive pest management strategies in fruit tree cultivation.

Effects of short-term high temperature at different life stages on reproductive fitness in Mythimna separata (Lepidoptera: Noctuidae)

Extreme heat events commonly occur under climate warming. All life stages of insects may experience the occurrence of extremely high temperatures. However, the effects of short-term extreme heat events on life-history traits remain unclear in most migratory pests. Here, we investigated the biological effects of short-term heat exposure (35 °C for 4 h) at different life stages on Mythimna separata Walker (Lepidoptera: Noctuidae), a typical migratory pest. We found that the reproductive sensitivity of pupae and adults was higher than that of 3rd-instar larvae. Increasing the frequency of heat exposure decreased the reproductive performance of M. separata at all life stages. Parental short-term heat exposures could cause transgenerational damage to offspring survival and reproductive fitness when the exposure frequency reached 3 times. Our results suggest that short-term exposure to extreme temperatures could impact reproductive fitness across different life stages in M. separata. This should be taken into consideration in the population prediction of migratory pests under climate change.

Experimental heatwaves reduce the effectiveness of ejaculates at occupying female reproductive tracts in a model insect

Globally, heatwaves have become more common with hazardous consequences on biological processes. Research using a model insect (Tribolium castaneum) found that 5-day experimental heatwave conditions damaged several aspects of male reproductive biology, while females remained unaffected. However, females' reproductive fitness may still be impacted, as insects typically store sperm from multiple males in specialized organs for prolonged periods. Consequently, using males which produce sperm with green fluorescent protein (GFP)-tagged sperm nuclei, we visualized in vivo whether thermal stress affects the ejaculate occupancy across female storage sites under two scenarios; (i) increasing time since insemination and (ii) in the presence of defending competitor sperm. We reconfirmed that sperm from heatwave-exposed males sired fewer offspring with previously mated females and provided new scenarios for in vivo distributions of heat-stress-exposed males' sperm. Sperm from heatwave-exposed males occupied a smaller area and were at lower densities across the females' storage sites. Generally, sperm occupancy decreased with time since insemination, and sperm from the first male to mate dominated the long-term storage site. Reassuringly, although heated males' ejaculate was less successful in occupying female tracts, they were not lost from female storage at a faster rate and were no worse than control males in their offensive ability to enter storage sites occupied by competitor sperm. Future work should consider the potential site-specificity of factors influencing sperm storage where amenable.

Interspecific differences in thermal tolerance landscape explain aphid community abundance under climate change

A single critical thermal limit is often used to explain and infer the impact of climate change on geographic range and population abundance. However, it has limited application in describing the temporal dynamic and cumulative impacts of extreme temperatures. Here, we used a thermal tolerance landscape approach to address the impacts of extreme thermal events on the survival of co-existing aphid species (Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi). Specifically, we built the thermal death time (TDT) models based on detailed survival datasets of three aphid species with three ages across a broad range of stressful high (34-40 °C) and low (-3∼-11 °C) temperatures to compare the interspecific and developmental stage variations in thermal tolerance. Using these TDT parameters, we performed a thermal risk assessment by calculating the potential daily thermal injury accumulation associated with the regional temperature variations in three wheat-growing sites along a latitude gradient. Results showed that M. dirhodum was the most vulnerable to heat but more tolerant to low temperatures than R. padi and S. avenae. R. padi survived better at high temperatures than Sitobion avenae and M. dirhodum but was sensitive to cold. R. padi was estimated to accumulate higher cold injury than the other two species during winter, while M. dirhodum accrued more heat injury during summer. The warmer site had higher risks of heat injury and the cooler site had higher risks of cold injury along a latitude gradient. These results support recent field observations that the proportion of R. padi increases with the increased frequency of heat waves. We also found that young nymphs generally had a lower thermal tolerance than old nymphs or adults. Our results provide a useful dataset and method for modelling and predicting the consequence of climate change on the population dynamics and community structure of small insects.

Alleviating Cell Lysate-Induced Inhibition to Enable RT-PCR from Single Cells in Picoliter-Volume Double Emulsion Droplets

Microfluidic droplet assays enable single-cell polymerase chain reaction (PCR) and sequencing analyses at unprecedented scales, with most methods encapsulating cells within nanoliter-sized single emulsion droplets (water-in-oil). Encapsulating cells within picoliter double emulsion (DE) (water-in-oil-in-water) allows sorting droplets with commercially available fluorescence-activated cell sorter (FACS) machines, making it possible to isolate single cells based on phenotypes of interest for downstream analyses. However, sorting DE droplets with standard cytometers requires small droplets that can pass FACS nozzles. This poses challenges for molecular biology, as prior reports suggest that reverse transcription (RT) and PCR amplification cannot proceed efficiently at volumes below 1 nL due to cell lysate-induced inhibition. To overcome this limitation, we used a plate-based RT-PCR assay designed to mimic reactions in picoliter droplets to systematically quantify and ameliorate the inhibition. We find that RT-PCR is blocked by lysate-induced cleavage of nucleic acid probes and primers, which can be efficiently alleviated through heat lysis. We further show that the magnitude of inhibition depends on the cell type, but that RT-PCR can proceed in low-picoscale reaction volumes for most mouse and human cell lines tested. Finally, we demonstrate one-step RT-PCR from single cells in 20 pL DE droplets with fluorescence quantifiable via FACS. These results open up new avenues for improving picoscale droplet RT-PCR reactions and expanding microfluidic droplet-based single-cell analysis technologies.

Function of Vitellogenin receptor gene in reproductive regulation of Zeugodacus cucurbitae (Coquillett) after short-term high-temperature treatment

Climate change has increased the frequency of extreme heat events. Zeugodacus cucurbitae (Coquillett) is an important tropical pest that typically changes its reproductive strategies in response to extremely high temperatures. Newly emerged adults of three consecutive generations (F₁, F₂, and F₃) of Z. cucurbitae (Coquillett) were exposed to 25°C, 33°C, 37°C, 41°C, and 45°C treatments for 1 h to clarify the effects of short-term high temperatures on its reproduction. The influence of these temperatures on reproduction was evaluated using indicators, such as egg number. Newly emerged adults were exposed to 25°C and 45°C treatments for 1 h, and the expression of Vitellogenin receptor (VgR) gene in females was interfered with siRNA, and silencing efficiency of RNAi was evaluated. Results showed that short-term high temperatures, except for F₁ treated at 45°C for 1 h to stimulate oviposition, exert a general adverse effect on the reproduction of Z. cucurbitae (Coquillett). All F₃ died after the 45°C treatment for 1 h. Silencing of the VgR gene resulted in the significant downregulation of VgR gene expression at both 24 and 72 h. The egg number, oviposition days, and hatchability of eggs were significantly lower than those of other treatment groups after interference, and the inhibition effect of egg number was the most evident, with a decrease of 88.4% and 95.2% at 25°C and 45°C, respectively, compared with that of the Control Check (CK). Ovarian development speed and diameter were also significantly lower than those of other treatment groups after the interference. The results of this study can provide a theoretical reference for the integrated control of Z. cucurbitae (Coquillett) during high-temperature seasons.

Low temperature triggers physiological and behavioral shifts in adult oriental armyworm, Mythimna separata

Migratory insects display diverse behavioral strategies in response to external environmental shifts, via energy allocation of migration-reproduction trade-offs. However, how migratory insects distribute energy between migration and reproduction as an adaptive strategy to confront temporary low temperatures remains unclear. Here, we used Mythimna separata, a migratory cereal crop pest, to explore the effects of low temperature on reproductive performance, behavior, and energy allocation. We found that the influence of low temperatures on reproduction was not absolutely negative, but instead depended on the intensity, duration, and age of exposure to low temperature. Exposure to 6°C for 24 h significantly accelerated the onset of oviposition and ovarian development, and increased the synchrony of egg-laying and lifetime fecundity in 1-day-old adults compared to the control, while female's flight capacity decreased significantly on the first and second day after moths were exposed to 6°C. Furthermore, the abdominal and total triglycerides levels of females decreased significantly from exposure to low temperature, but their thoracic triglyceride content was significantly higher than the control on the third and fourth day. These results indicated that low temperatures induced M. separata to reduce energy investment for the development of flight system. This resulted in the shifting of moths from being migrants to residents during the environmental sensitive period (first day post-emergence). This expands our understanding of the adaptive strategy employed by migratory insects to deal with low temperatures and aids in the management of this pest species in China.

Impacts of Non-Lethal High-Temperature Stress on the Development and Reproductive Organs of Bradysia odoriphaga

Simple Summary

Bradysia odoriphaga is a soil-dwelling insect native to China, and its preferred host is Chinese chives. In this study, non-lethal high-temperature as an important limiting factor to affect the population and development of B. odoriphaga was assessed. Meanwhile, the physiological mechanism on non-lethal high-temperature to reduce the population was also identified. These would lay a key theoretical foundation for the future development of high-temperature products for environment friendly pest control strategies.

Abstract

Bradysia odoriphaga is an agricultural pest in China’s vegetable industry. In this study, pupae and adults were exposed to various non-lethal high-temperatures. The results demonstrated a decreased rate of eclosion once the pupae were exposed to temperatures exceeding 37 °C for 1 h. No effect on the lifespan of unmated female adults was observed after exposure to temperature stress, while unmated male adult lifespan decreased (>37 °C for 2 h). The size of the testis and ovaries for unmated male and female adults decreased, as did the fecundity and egg hatching rate for mated females. Compared with the control group (25 °C), the testis size of unmated male adults decreased after high-temperature stress followed by recovery at 25 °C for 1 h, though the size of the ovaries of female adults did not change. Additionally, the size of the testis and ovaries for unmated male and female adults decreased following high-temperature stress and 24 h of recovery at 25 °C. High temperatures affected males more than females; 37 °C is the critical temperature to control the population of B. odoriphaga. These results lay the foundation for the future development of environmentally friendly high-temperature prevention and pest-control strategies.

Flight and Reproduction Variations of Rice Leaf Roller, Cnaphalocrocis medinalis in Response to Different Rearing Temperatures

Simple Summary

Temperature directly affects the development, adult reproduction, and flight capacity in migratory insects. However, the adaptive strategies applied by some migratory insects to cope with stressful temperatures throughout their life cycles are not well understood. In this study, we evaluated the effects of rearing temperatures in the immature stage (from egg to pupae stage) on the immature development, adult reproduction flight ability, and migratory behavior of Cnaphalocrocis medinalis, one major facultative long-distance migratory pest feeding on rice. Our data suggest that immature C. medinalis that experienced different rearing temperatures had different developmental, reproductive, and migration patterns. Cnaphalocrocis medinalis reared under high temperatures had weaker reproductive capacity and stronger flight potentiality, which might be more likely to trigger the migration. However, those reared at low temperatures in the immature stage had an accelerated reproduction but relative weaker flight ability, which might weaken the migratory motivation of adults.

Abstract

Understanding how species that follow different life-history strategies respond to stressful temperature can be essential for efficient treatments of agricultural pests. Here, we focused on how the development, reproduction, flight, and reproductive consequences of migration of Cnaphalocrocis medinalis were influenced by exposure to different rearing temperatures in the immature stage. We found that the immature rice leaf roller that were reared at low temperatures (18 and 22 °C) developed more slowly than the normal temperature 26 °C, while those reared at high temperatures (34 °C) grew faster. Female adults from low immature stage rearing temperatures showed stronger reproductive ability than those at 26 and 34 °C, such as the preoviposition period (POP) significantly decreased, while the total lifetime fecundity obviously increased. However, 34 °C did not significantly reduce the reproductive performances of females compared to 26 °C. On the contrary, one relative decreased tendency of flight capacity was found in the lower immature temperature treatments. Furthermore, flight is a costly strategy for reproduction output to compete for limited internal resources. In the lower temperature treatments, after d1-tethered flight treatment, negative reproductive consequences were found that flight significantly decreased the lifetime fecundity and mating frequency of females from low rearing temperatures in the immature stage compared to the controls (no tethered-flight). However, in the 26 and 34 °C treatments, the same flight treatment induced a positive influence on reproduction, which significantly reduced the POP and period of first oviposition (PFO). The results suggest that the experience of relative high temperatures in the immature stage is more likely to trigger the onset of migration, but lower temperatures in the immature stage may induce adults to have a greater resident propensity with stronger reproductive ability.

Dynamics of heat shock protein responses to thermal stress changes after metamorphosis in a lepidopteran insect

In the last decade, unexpected high temperatures have been frequent in spring and early summer. Numerous studies have shown that such thermal stress has substantial effects on life-history traits that influence fitness of insects, but few have examined expression dynamics of heat shock proteins (Hsps) across developmental stages, especially as regards potential carry-over effects at the transcriptional level across metamorphosis. We exposed pupae of the oriental fruit moth ("OFM," Grapholita molesta Busck) to mild heat stress (38°C, 6 h) and then quantified expression patterns of six Hsps (Hsp90, 70, 60, 40, 21, and 11) from pupal through adult stages. Almost all Hsps showed a higher expression immediately after pupae were heat-stressed, but later dropped to normal levels after metamorphosis. Although upregulation of Hsps is transient and the effects carry over longer to early adult stage, upregulation will nonetheless have positive effects on adult fitness. The fitness of some insects may benefit from higher expression of chaperon genes after mild stress, in the form of higher fecundity and longer lifespan, as a carry-over effect. These results suggest that mild thermal stress can change genetic expression that later boosts adult fitness through a cascade effect.

Survive a Warming Climate: Insect Responses to Extreme High Temperatures

Global change includes a substantial increase in the frequency and intensity of extreme high temperatures (EHTs), which influence insects at almost all levels. The number of studies showing the ecological importance of EHTs has risen in recent years, but the knowledge is rather dispersed in the contemporary literature. In this article, we review the biological and ecological effects of EHTs actually experienced in the field, i.e., when coupled to fluctuating thermal regimes. First, we characterize EHTs in the field. Then, we summarize the impacts of EHTs on insects at various levels and the processes allowing insects to buffer EHTs. Finally, we argue that the mechanisms leading to positive or negative impacts of EHTs on insects can only be resolved from integrative approaches considering natural thermal regimes. Thermal extremes, perhaps more than the gradual increase in mean temperature, drive insect responses to climate change, with crucial impacts on pest management and biodiversity conservation.

Validating measurements of acclimation for climate change adaptation

Acclimation and other forms of plasticity that can increase stress resistance feature strongly in discussions surrounding climate change impacts or vulnerability projections of insects and other ectotherms. There is interest in compiling databases for assessing the adequacy of acclimation for dealing with climate change. Here, we argue that the nature of acclimation is context dependent and therefore that estimates summarised across studies, especially those that have assayed stress using diverse methods, are limited in their utility when applied as a standardized metric or to a single general context such as average climate warming. Moreover, the dynamic nature of tolerances and acclimation drives important variation that is quickly obscured through many summary statistics or even in effect size analyses; retaining a strong focus on the temporal-level, population-level and treatment-level variance in forecasting climate change impacts on insects is essential. We summarise recent developments within the context of climate change and propose how future studies might validate the role of acclimation by integration across field studies and mechanistic modelling. Despite arguments to the contrary, to date no studies have convincingly demonstrated an important role for acclimation in recent climate change adaptation of insects. Paramount to these discussions is i) developing a strong conceptual framework for acclimation in the focal trait(s), ii) obtaining novel empirical data dissecting the fitness benefits and consequences of acclimation across diverse contexts and timescales, with iii) better coverage of under-represented geographic regions and taxa.

Lethal and sublethal effect of heat shock on Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Temperature is an important abiotic environmental factor, and is responsible for various kinds of behavioral and physiological changes in living organisms. Induced heat shock is associated with feeding behaviour, reproduction and reactive oxygen species (ROS) generation that causes oxidative damage. In this experiment, we examined the lethal and sublethal effects of heat shock on reproduction, feeding behaviour and antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and peroxidases (POD) in P. solenopsis. Results showed that males were highly susceptible to heat shock treatments than females, as LTemp₅₀ values were 43.8 °C for males and 45.11 °C for females. Heat shock events non-significantly affected the fecundity in female only treated adults and significantly affected the both sexes heat treated adults, it increased the xylem feeding duration, percentage of xylem feeding adults and reduce the phloem feeding duration and percentage of phloem feeding adults. Similarly it alter the antioxidant enzymes activities, an increase of CAT, SOD and POD activities were noticed in response to highest intensity of heat shock while a reduction of CAT and SOD activity were noticed in response to lowest intensity of heat shock compared to control (30 °C). These results suggest that heat shock may result in loss of body water and induce oxidative stress in P. solenopsis. However, antioxidant enzymes play a significant role in overcoming the oxidative damage.

Effects of Non-Lethal High-Temperature Stress on Bradysia odoriphaga (Diptera: Sciaridae) Larval Development and Offspring

Throughout China, the dipteran pest Bradysia odoriphaga significantly reduces Chinese chive production; therefore, identifying conditions that influence its growth and development is crucial for developing ecological regulation strategies. In this study, different non-lethal high temperatures and treatment durations were used to stress the third-instar larvae of B. odoriphaga, and the effects of this treatment on their growth and offspring were recorded and analyzed. The results showed that the average larval mortality increased with increased temperature and prolonged exposure times. After stress treatment at 40 °C for 2 h, 100% of larvae died within 5 days, which was not significantly different from the 5-day average larval mortality (90.66%) after stress at 37 °C for 4 h, but significantly higher than the 5-day average larval mortality (72.00%) after stress at 40 °C for 1 h. After 5 days, all still-living larvae could pupate, and there was no significant difference in average pupal period after pupation. However, the eclosion rate of subsequent pupae decreased with increased temperature and prolonged exposure times, and were only 43.00% and 42.73% after larvae were stressed at 37 °C for 4 h and 40 °C for 1 h, respectively. After eclosion into adults, there was no significant difference in the lifespan of unmated female adults, while the lifespan of unmated male adults was significantly reduced to 1.67 d and 2 d after larvae were stressed at 37 °C for 4 h and 40 °C for 1 h, respectively. However, there was no significant difference in male and female adult longevity after mating. There was no significant difference in oviposition or egg hatchability. This indicates that non-lethal high temperature at 37 °C for 4 h can hinder development and allow control of B. odoriphaga. There is great potential for non-lethal high temperature to be applied in the field to control agricultural pests.

Response Mechanism of Oviposition and Relevant Protein Expression of Bactrocera cucurbitae (Coquillet) to Short-Term High-Temperature Conditions

Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) is an important pest of vegetables in Asia, the Middle East, Africa, and Hawaii. High temperature can significantly influence B. cucurbitae reproduction. The effect of short-term high-temperature exposure on proteins that affect oviposition was analyzed by proteomics. Among six key target genes for oviposition, the expression of Vitellogenin-1, Vitellogenin-2, and Vitellogenin receptor was similar in B. cucurbitae exposed to higher temperature compared to controls. However, levels of Vitellogenin-3 were reduced. Juvenile hormone (Jh)-inducible protein was downregulated and then upregulated, while the expression of Jh-epoxide hydrolase-2 showed the opposite Jh-inducible protein trend. Therefore, short-term high-temperature stress can cause differential expression of proteins related to oviposition in B. cucurbitae, which in turn further triggers the hormesis of oviposition. High-temperature conditions have become more frequent because of climate warming and are predicted to continue. The data indicate that climate effects on insect reproduction pose a significant threat to agriculture in a world of increasing population.

Sporadic short temperature events cannot be neglected in predicting impacts of climate change on small insects

Climate warming is characterized by increase in extreme heat events (EHEs). EHEs and mild temperature periods alternate with each other and form complex climate scenarios. Among these scenarios, low-frequency and short-duration extreme heat events during long mild periods (sporadic short EHEs) and low-frequency and short-duration mild periods during long extreme heat events (sporadic short mild periods) commonly occur in nature. The biological effects of these two types of temperature events have not been thoroughly elucidated to date. To clarify the biological effects of these temperature events on organisms, we selected the English grain aphid, a globally important cereal pest, as our model system. We exposed aphids to simulated 24-h diurnal fluctuating temperatures, inserted these events during the wheat growing season and then investigated development, adult longevity, fecundity, survival, and demographic parameters. We found that sporadic short mild periods during a long EHE could improve their life history traits. Increasing the duration of mild periods from 1 day to 2 days did not significantly change their demographic performance. Sporadic short EHEs during a long mild period did not significantly affect vital rates, while increasing the duration of EHEs from 1 day to 2 days worsened the aphids' performance. We found that short mild episodes in the hot season may benefit small insects to buffer long duration heatwaves. We discussed how sporadic short mild periods during a long EHE supplied aphids a chance to recover from heat stress. Thus, we suggest that sporadic temperature events should be considered in population prediction of small insects under climate change and should be integrated into pest management.

Influence of high-temperature exposure on the mating, oviposition and thermotaxis of Bactrocera cucurbitae (Coquillet) (Diptera:Tephritidae)

Background

Bactrocera cucurbitae (Coquillett) is an important pest of cucurbit crops and certain vegetables in Asia, the Middle East, Africa and Hawaii. Most studies on B. cucurbitae have focussed on the effects of prolonged high temperature and very few have examined the effects of short-term exposures to high-temperature on behaviour.

Results

In this study, short-term of high-temperature treatments of 33°C, 37°C, 41°C and 45°C were maintained for 1-3hr, and long-term, variable high-temperature treatments were established that consisted of experienced one, two and three times high temperatures stages to 31°C, 33°C, 34°C, 35°C, 36°C, 37°C, 41°C and 45°C for 7hr. We compared the effects of the different high temperatures regimes changes treatments on the mating, oviposition and thermotactic taxis of the flies. The results showed that exposure to a 45°C/1hr treatment, delayed both initiation of mating and oviposition for 8 hr relative to the control but mating and was observed 41 times and oviposition 47 times. By comparison, in the control, mating commenced immediately and was observed 38.3 times and oviposition was observed 41.3 times. Under the other treatments, all the indices for the flies declined with the increase in temperature and duration of exposure.

Conclusion

Results showed that 1hr of exposure to 45°C significantly stimulated mating, oviposition and thermotactic behaviour of the flies. These results could improve our understanding of the mechanisms responsible for the population dynamics of B. cucurbitae during the high-temperature season.

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.

The clandestine organs of the endocrine system

This review analyzes what could be regarded as the "clandestine organs" of the endocrine system: the gut microbiome, the immune system, and the stress system. The immune system is very closely related to the endocrine system, with many intertwined processes and signals. Many researchers now consider the microbiome as an 'organ' that affects the organism at many different levels. While stress is certainly not an organ, it affects so many processes, including endocrine-related processes, that the stress response system deserved a special section in this review. Understanding the connections, effects, and feedback mechanisms between the different "clandestine organs" and the endocrine system will provide us with a better understanding of how an organism functions, as well as reinforce the idea that there are no independent organs or systems, but a complex, interacting network of molecules, cells, tissues, signaling pathways, and mechanisms that constitute an individual.

Are adult life history traits in oriental fruit moth affected by a mild pupal heat stress?

Thermal stress at one life stage can affect fitness at a later stage in ectotherms with complex life cycles. Most relevant studies have focused on extreme stress levels, but here we also show substantial fitness effects in a moth when pupae are exposed to a relatively mild and sublethal heat stress. We consider the impact of a 35°C heat stress of 2h in three geographically separate populations of the oriental fruit moth (OFM, Grapholita molesta) from northern, middle and southern China. Heat stress negatively affected fecundity but increased adult heat resistance and adult longevity. Fitness effects were mostly consistent across populations but there were also some population differences. In the Shenyang population from northern China, there was a hormetic effect of heat on female longevity not evident in the other populations. Adults from all populations had higher LT₅₀s due to heat stress after pupal exposure to the sublethal stress. These results highlight that the pupal stage is a particularly sensitive window for development and they have implications for seasonal adaptation in uncertain environments as well as changes in pest dynamics under climate warming.

Plastic and evolutionary responses to heat stress in a temperate dung fly: negative correlation between basal and induced heat tolerance?

Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot-acclimation or non-acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat-shocked flies, but in the absence of heat stress hot-acclimated flies had reduced life spans relative to non-acclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness-related traits.