Insects in fluctuating thermal environments

Body size decline during thermal evolution is only detected at mild temperature

Body size is a key morphological trait that affects physiology and metabolism, as well as other relevant traits such as fertility and mating success. Some evidence points to a trend of shrinking body size with increasing temperature, but this is far from unequivocal. Here, we assess the evolution of body size under a warming environment in experimentally evolved Drosophila subobscura populations from two distinct geographical origins, tested in both ancestral and warming environments. We observed a decrease in body size in the warming populations, but only in the lower-latitude populations and only when tested in the ancestral (control) environment. The absence of a body size response in the warming environment may be owing to a balance between forces promoting thermodynamic stability-leading to a tendency for body size to decrease-and selection for increased reproductive output-leading to an increase in body size. Our findings indicate that body size variation is complex, with genotype-by-environment interactions occurring. This may explain the lack of consistency across studies. This highlights that predictions of body size evolution under climate warming are not straightforward and emphasizes the need for considering intra- and inter-specific variation in future studies.

Analysis of resting status reveals distinct elevational variation in metabolisms of lizards

Animals spend a considerable proportion of their life span at rest. However, resting status has often been overlooked when investigating how species respond to environmental conditions. This may induce a large bias in understanding the local adaptation of species across environmental gradients and their vulnerability to potential environmental change. Here, we conducted an empirical study on montane agamid lizards, combined with mechanistic modeling, to compare elevational variations in body temperature and metabolisms (cumulative digestion and maintenance cost) between resting and active status. Our study on three populations of an agamid lizard along an elevational gradient revealed a trend of decreasing body temperature toward higher elevations, the main contributor of which was resting status of the lizards. Using population-specific reaction norms, we predicted greater elevational variation in hourly and cumulative digestion for resting lizards than for active lizards. Climate-change impacts, estimated as the change in cumulative digestion, also show greater elevational variation when resting status is factored into the analysis. Further, our global analysis of 98 agamid species revealed that in about half of their combined distributional range, the contribution of resting status in determining the elevational variation in cumulative digestion and maintenance cost of lizards was greater than the contribution made by a lizard's active status. Our study highlights the importance of considering resting status when investigating how species respond to environmental conditions, especially for those distributed over tropical and subtropical mountain areas.

Temperature variability regulates the interactive effects of warming and pharmaceutical on aquatic ecosystem dynamics

Climate warming and pharmaceutical contaminants have profound impacts on population dynamics and ecological community structure, yet the consequences of their interactive effects remain poorly understood. Here, we explore how climate warming interacts with pharmaceutical-induced boldness change to affect aquatic ecosystems, built on an empirically well-informed food-chain model, consisting of a size-structured fish consumer, a zooplankton prey, and a fish predator. Climate warming is characterized by both daily mean temperature (DMT) and diurnal temperature range (DTR) in our model. Results show that DMT and high levels of species' boldness are the primary drivers of community instability. However, their interactive effects can lead to diverse outcomes: from predator collapse to coexistence with seasonality-driven cycles and coexistence with population interaction-driven cycles. The interactive effects are significantly modulated by daily temperature variability, where moderate DTR counteracts the destabilizing interactive effects by increasing consumer reproduction, while large temperature variability considerably reduces consumer biomass, destabilizing the community at high mean temperatures. Our analyses disentangle the respective roles of DMT, DTR and boldness in mediating the response of aquatic ecosystems to the impacts from pharmaceutical contaminants in the context of climate warming. The interactive effects of the environmental stressors reported here underscore the pressing need for studies aimed at quantifying the cumulative impacts of multiple environmental stressors on aquatic ecosystems.

HSF1 is required for cellular adaptation to daily temperature fluctuations

The heat shock response (HSR) is a universal mechanism of cellular adaptation to elevated temperatures and is regulated by heat shock transcription factor 1 (HSF1) or HSF3 in vertebrate endotherms, such as humans, mice, and chickens. We here showed that HSF1 and HSF3 from egg-laying mammals (monotremes), with a low homeothermic capacity, equally possess a potential to maximally induce the HSR, whereas either HSF1 or HSF3 from birds have this potential. Therefore, we focused on cellular adaptation to daily temperature fluctuations and found that HSF1 was required for the proliferation and survival of human cells under daily temperature fluctuations. The ectopic expression of vertebrate HSF1 proteins, but not HSF3 proteins, restored the resistance in HSF1-null cells, regardless of the induction of heat shock proteins. This function was associated with the up-regulation of specific HSF1-target genes. These results indicate the distinct role of HSF1 in adaptation to thermally fluctuating environments and suggest association of homeothermic capacity with functional diversification of vertebrate HSF genes.

Evolutionary adaptation under climate change: Aedes sp. demonstrates potential to adapt to warming

Climate warming is expected to shift the distributions of mosquitoes and mosquito-borne diseases, facilitating expansions at cool range edges and contractions at warm range edges. However, whether mosquito populations could maintain their warm edges through evolutionary adaptation remains unknown. Here, we investigate the potential for thermal adaptation in Aedes sierrensis, a congener of the major disease vector species that experiences large thermal gradients in its native range, by assaying tolerance to prolonged and acute heat exposure, and its genetic basis in a diverse, field-derived population. We found pervasive evidence of heritable genetic variation in acute heat tolerance, which phenotypically trades off with tolerance to prolonged heat exposure. A simple evolutionary model based on our data shows that the estimated maximum rate of evolutionary adaptation in mosquito heat tolerance typically exceeds that of projected climate warming under idealized conditions. Our findings indicate that natural mosquito populations may have the potential to track projected warming via genetic adaptation. Prior climate-based projections may thus underestimate the range of mosquito and mosquito-borne disease distributions under future climate conditions.

Heat stress-induced oviposition behavioral change correlates with sperm damage in the pine sawyer beetle, Monochamus alternatus

BACKGROUND

Global climate change is causing an increase in extreme high temperatures (EHTs), which subject insects to unprecedented stress. Behavior plasticity in response to EHTs, particularly oviposition behavior, is important for the persistence and outbreak of insect populations. Investigating the plasticity of oviposition behavior and its underlying mechanisms has theoretical importance to pest management, but knowledge gaps still remain.

RESULTS

Herein, we characterized the reproductive traits of Monochamus alternatus, a dominant insect vector of the destructive pine wilt disease, including oviposition behavioral patterns, fecundity, offspring fitness and sperm viability, under simulated heatwave conditions in the laboratory. The results showed that (i) EHTs induced a novel oviposition behavior, whereby females deposited multiple eggs into a single groove rather than laying one egg per groove under normal condition; (ii) EHTs exerted stage- and sex-specific effects on fecundity, offspring fitness and sperm viability; and (iii) there was a significant correlation between frequency of the novel oviposition strategy and sperm viability.

CONCLUSION

We hypothesized that this beetle pest has the ability to flexibly shift towards a low-cost oviposition strategy to counteract the fitness costs caused by heat stress. Taken together, these findings provide a theoretical foundation for personalized pest management strategies in the context of climate change. © 2024 Society of Chemical Industry.

The Effect of Temperature Variability on Biological Responses of Ectothermic Animals-A Meta-Analysis

Climate change is altering temperature means and variation, and both need to be considered in predictions underpinning conservation. However, there is no consensus in the literature regarding the effects of temperature fluctuations on biological functions. Fluctuations may affect biological responses because of inequalities from non-linear responses, endocrine regulation or exposure to damaging temperatures. Here we establish the current state of knowledge of how temperature fluctuations impact biological responses within individuals and populations compared to constant temperatures with the same mean. We conducted a meta-analysis of 143 studies on ectothermic animals (1492 effect sizes, 118 species). In this study, 89% of effect sizes were derived from diel cycles, but there were no significant differences between diel cycles and shorter (<8 h) or longer (>48 h) cycles in their effect on biological responses. We show that temperature fluctuations have little effect overall on trait mean and variance. Nonetheless, temperature fluctuations can be stressful: fluctuations increased 'gene expression' in aquatic animals, which was driven mainly by increased hsp70. Fluctuating temperatures also decreased longevity, and increased amplitudes had negative effects on population responses in aquatic organisms. We conclude that mean temperatures and extreme events such as heat waves are important to consider, but regular (particularly diel) temperature fluctuations are less so.

High-temperature responses of Myzus persicae and its parasitoid Aphidius gifuensis in relation to heat level, duration and developmental stage

BACKGROUND

Understanding how parasitoids respond to temperature is crucial for improving biological control strategies under the context of global warming. This study examined the suitability of Myzus persicae and its parasitoid Aphidius gifuensis to varying temperature conditions, as well as the stage-specific response of A. gifuensis to high temperatures.

RESULTS

High temperatures had a significant impact on the both M. persicae and A. gifuensis. When exposed to 36°C, M. persicae developed more slowly and produced smaller adults compared to control, regardless of the duration of exposure (2, 4 or 6 h); additionally, the survival rate of M. persicae nymphs sharply decreased under these conditions. Exposure to 36°C for 4 h negatively impacted the development of A. gifuensis. Female parasitoids exposed to 32°C developed into smaller adults, whereas males exposed to all three temperature levels were smaller compared to control group. Female parasitoids exposed to high temperatures, regardless of the specific heat level and duration, exhibited reduced longevity and decreased fecundity. None of the parasitoids exposed to 36°C for 6 h daily developed into adults. Heat treated during early developmental stages (2 and 4 days old) had a greater influence on parasitoid development, whereas heat treatment at 4 and 6 days old had a more significant impact on its fecundity.

CONCLUSION

High temperatures not only directly affected the performance of A. gifuensis, but also exerted indirect effects by influencing the quality of the host aphids M. persicae. The deleterious effects of high temperature on larvae can persist into the adult stage, affecting the longevity and reproduction of adults. These findings are important for the utilization of A. gifuensis in the control of M. persicae in warming environments. © 2024 Society of Chemical Industry.

Thresholds and interactive effects of BPA-gradient and temperature on life history traits of Daphnia magna

Bisphenol A (BPA), a synthetic organic compound widely used in the production of plastics, is recognized as an emerging contaminant because of its toxicity and the potential risks associated with bioaccumulation in organisms. Despite potential environmental hazards, there is a lack of studies examining BPA toxicity mechanisms and its potential impact on various trophic levels, with even fewer exploring whether global stressors such as temperature can affect the toxicity of BPA in organisms. Our aim was to assess the combined impact of BPA and varying temperature regimes on life-history traits in Daphnia magna. Our results revealed a significant impact of BPA on the growth, reproduction, and accumulated moulting of D. magna, with adverse effects primarily associated with the assimilation of BPA in algae rather than the BPA present in the medium, pointing to a trophic transfer mechanism. The interactive effect between BPA and temperature demonstrated a slight stimulatory effect of low BPA level on D. magna growth rate under warming constant conditions, but an inhibitory under warming fluctuating temperatures. Additionally, a BPA threshold was identified, below which growth became temperature-dependent. This study emphasizes the crucial role of considering temperature in predicting how toxins may affect Daphnia within aquatic food webs.

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.

Occurrence and potential diffusion of pine wilt disease mediated by insect vectors in China under climate change

BACKGROUND

Pine wilt disease (PWD), a major international quarantined forest pest, causes serious ecological and economic damage to Pinus species in Asia and Europe. In China, PWD has spread northeasterly and northwesterly beyond its original northern limits. Consequently, an evaluation of the insect vector-mediated occurrence and potential diffusion of PWD is needed to identify important transmission routes and control the spread of disease.

RESULTS

An optimized MaxEnt model was used to assess the current and future geographical distribution of Bursaphelenchus xylophilus and its insect vectors in China. The predicted suitable area for B. xylophilus colonization is currently 212.32 × 104 km2 and mainly concentrated in Central, East, Southwest and South China, although is anticipated to include the northwestern regions of China in the future. As for the insect vectors, Monochamus alternatus and M. saltuarius are expected to spread toward the northwest and southwest, respectively. The maximum predicted dispersion area of PWD mediated by M. alternatus, M. saltuarius and both species was 91.85 × 104, 218.76 × 104 and 29.99 × 104 km2, respectively, with potential diffusion areas being anticipated to increase in the future. Both the suitable probabilities and areas of B. xylophilus and its insect vectors were found to vary substantially along the latitudinal gradient, with the latitudinal range of these species being predicted to expand in the future.

CONCLUSION

This is the first study to investigate the potential diffusion areas of PWD mediated by insect vectors in China, and our finding will provide a vital theoretical reference and empirical basis for developing more effective management strategies for the control of PWD in China. © 2024 Society of Chemical Industry.

Heat stress and host-parasitoid interactions: lessons and opportunities in a changing climate

Ongoing climate change is increasing the frequency and magnitude of high-temperature events (HTEs), causing heat stress in parasitoids and their hosts. We argue that HTEs and heat stress should be viewed in terms of the intersecting life cycles of host and parasitoid. Recent studies illustrate how the biological consequences of a given HTE may vary dramatically depending on its timing within these lifecycles. The temperature sensitivity of host manipulation by parasitoids, and by viral endosymbionts of many parasitoids, can contribute to differing responses of hosts and parasitoids to HTEs. In some cases, these effects can result in reduced parasitoid success and increased host herbivory and may disrupt the ecological interactions between hosts and parasitoids. Because most studies to date involve endoparasitoids of aphid or lepidopteran hosts in agricultural systems, our understanding of heat responses of host-parasitoid interactions in natural systems is quite limited.

Influence of environmental, geographic, socio-demographic, and epidemiological factors on presence of malaria at the community level in two continents

The interactions of environmental, geographic, socio-demographic, and epidemiological factors in shaping mosquito-borne disease transmission dynamics are complex and changeable, influencing the abundance and distribution of vectors and the pathogens they transmit. In this study, 27 years of cross-sectional malaria survey data (1990-2017) were used to examine the effects of these factors on Plasmodium falciparum and Plasmodium vivax malaria presence at the community level in Africa and Asia. Monthly long-term, open-source data for each factor were compiled and analyzed using generalized linear models and classification and regression trees. Both temperature and precipitation exhibited unimodal relationships with malaria, with a positive effect up to a point after which a negative effect was observed as temperature and precipitation increased. Overall decline in malaria from 2000 to 2012 was well captured by the models, as was the resurgence after that. The models also indicated higher malaria in regions with lower economic and development indicators. Malaria is driven by a combination of environmental, geographic, socioeconomic, and epidemiological factors, and in this study, we demonstrated two approaches to capturing this complexity of drivers within models. Identifying these key drivers, and describing their associations with malaria, provides key information to inform planning and prevention strategies and interventions to reduce malaria burden.

Heat waves induce milkweed resistance to a specialist herbivore via increased toxicity and reduced nutrient content

Over the last decade, a large effort has been made to understand how extreme climate events disrupt species interactions. Yet, it is unclear how these events affect plants and herbivores directly, via metabolic changes, and indirectly, via their subsequent altered interaction. We exposed common milkweed (Asclepias syriaca) and monarch caterpillars (Danaus plexippus) to control (26:14°C, day:night) or heat wave (HW) conditions (36:24°C, day:night) for 4 days and then moved each organism to a new control or HW partner to disentangle the direct and indirect effects of heat exposure on each organism. We found that the HW directly benefited plants in terms of growth and defence expression (increased latex exudation and total cardenolides) and insect her'bivores through faster larval development. Conversely, indirect HW effects caused both plant latex and total cardenolides to decrease after subsequent herbivory. Nonetheless, increasing trends of more toxic cardenolides and lower leaf nutritional quality after herbivory by HW caterpillars likely led to reduced plant damage compared to controls. Our findings reveal that indirect impacts of HWs may play a greater role in shaping plant-herbivore interactions via changes in key physiological traits, providing valuable understanding of how ecological interactions may proceed in a changing world.

Acclimation temperature influences the thermal sensitivity of injury accumulation in Folsomia candida at extreme low and high temperatures

The importance of thermal acclimation for the Thermal Death Time (TDT) landscape of the common soil living springtail, Folsomia candida (Collembola, Isotomidae), was investigated. To this aim, we acclimated adult springtails at 10 °C (cold-acclimation) and 20 °C (warm-acclimation), respectively. In static thermal tolerance assays, we found the relationship between survival and exposure time at a number of stressful high and low temperatures. Using logistic modelling, we found, at each exposure temperature, the time until 50% mortality had been reached (Lt50). The exponential functions of TDT curves were found by linear regression of log10 Lt50 values against exposure temperature. Results showed that cold acclimation significantly increased cold tolerance and increased the temperature dependence of cold injury accumulation rate (increased the slope by 4 orders of magnitude) in F. candida. Hence, cold acclimation changed the status of this species from chill-susceptible to moderately chill-tolerant. The cellular injury accumulation at sub-zero temperatures was not related to freezing of body water in this study. Congruently, we found a significant negative effect of cold acclimation on heat tolerance and that cold acclimation decreased the thermal sensitivity of the heat injury accumulation rate. Different slopes of the TDT curves between acclimation groups indicated that acclimation shifted the proportional importance of cellular injury mechanisms or the nature of injury mechanisms. Finally, we compare and combine the TDT curves at extreme high and low temperatures with previously published results on longevity at benign temperatures (from 0 to 30 °C) and describe the full thermal niche of F. candida.

To live or let die? Epigenetic adaptations to climate change-a review

Anthropogenic activities are responsible for a wide array of environmental disturbances that threaten biodiversity. Climate change, encompassing temperature increases, ocean acidification, increased salinity, droughts, and floods caused by frequent extreme weather events, represents one of the most significant environmental alterations. These drastic challenges pose ecological constraints, with over a million species expected to disappear in the coming years. Therefore, organisms must adapt or face potential extinctions. Adaptations can occur not only through genetic changes but also through non-genetic mechanisms, which often confer faster acclimatization and wider variability ranges than their genetic counterparts. Among these non-genetic mechanisms are epigenetics defined as the study of molecules and mechanisms that can perpetuate alternative gene activity states in the context of the same DNA sequence. Epigenetics has received increased attention in the past decades, as epigenetic mechanisms are sensitive to a wide array of environmental cues, and epimutations spread faster through populations than genetic mutations. Epimutations can be neutral, deleterious, or adaptative and can be transmitted to subsequent generations, making them crucial factors in both long- and short-term responses to environmental fluctuations, such as climate change. In this review, we compile existing evidence of epigenetic involvement in acclimatization and adaptation to climate change and discuss derived perspectives and remaining challenges in the field of environmental epigenetics. Graphical Abstract.

Cold tolerance and metabolism of red-haired pine bark beetle Hylurgus ligniperda (Coleoptera: Curculionidae) during the overwintering period

Hylurgus ligniperda invaded Shandong, China, through imported forest timber, posing a threat to China's forest health. Exotic insects with broad environmental tolerance, including low temperatures, may have a better chance of surviving the winters and becoming invasive. Understanding the cold-tolerance strategies of H. ligniperda may help to design sustainable pest management approaches. In this study, we aim to investigate the cold-tolerance ability and relevant physiological indicators in overwintering H. ligniperda adults to determine any possible overwintering strategies. Supercooling points (SCPs) for adults H. ligniperda differed significantly across months and reached the lowest level in the mid- and post-overwintering period, the minimum SCPs -6.45 ± 0.18 °C. As the cold exposure temperature decreased, the survival rate of adults gradually decreased, and no adult survived more than 1 day at -15 °C, and the LLT50 for 1 day was -7.1 °C. Since H. ligniperda adults can survive internal ice formation, they are freeze-tolerant insects. Throughout the overwintering period, the SCPs and the water, protein, sorbitol, and glycerol content in adults decreased initially and then increased. We reported significant correlations between total protein, sorbitol, trehalose, and glycerol content in the beetles and SCPs. Glycogen, lipid, protein, trehalose, and sorbitol content in adult beetles may directly affect their cold-tolerance capacity and survival during winter. This study provides a physiological and biochemical basis for further study of metabolism and cold-tolerance strategies in H. ligniperda adults, which may help predict population dynamics and distribution potential of pests.

The consequences of heatwaves for the reproductive success and physiology of the wingless sub-Antarctic fly Anatalanta aptera

Sub-lethal effects of warming temperatures are an important, yet sometimes overlooked impact of climate change that may threaten the long-term survival of numerous species. This, like many other effects of climate change, is especially concerning for cold-adapted ectotherms living in rapidly warming polar regions. This study examines the effects of warmer temperatures on cold-adapted Diptera, using the long-lived sub-Antarctic sphaerocerid fly, Anatalanta aptera, as a focal species. We conducted two experiments to assess heat stress in adult flies, one varying the intensity of the heat stress (daily heating from 4 °C to 8 °C, 20 °C, or 24 °C) and one varying the frequency of heat stress exposure (heating from 4 °C to 12 °C every one, two, or three days) and examined consequences for reproductive success and metabolic responses. We found that more heat stress reduced reproductive output, but not timing of reproduction. Surprisingly, individuals sampled at different times during heat stress exposure were undifferentiable when all metabolite concentrations were analysed with redundancy analysis, however some individual metabolites did exhibit significant differences. Overall, our findings suggest that warmer temperatures in the sub-Antarctic may put this species at greater risk, especially when combined with other concurrent threats from biological invasions.

Basking improves but winter warming worsens overwinter survival in the linden bug

The present study investigates the effects of rare winter basking behavior (observed in wild populations of the Linden bug, Pyrrhocoris apterus) and the effects of winter warming (predicted by climate models) on overwinter survival and physiology of P. apterus. The insects were exposed to scenarios simulating basking and winter warming in the laboratory. Part of the insects were exposed to real winters under semi-natural conditions in the field for comparison. The results show a clear positive effect of winter basking, implying that basking behavior is critical for overwinter survival in P. apterus. In contrast, winter warming was found to have a strong negative effect on overwinter survival, potentially representing a threat to central European populations of P. apterus. Physiological parameters (mass, water content, SCP, energy reserves) measured in this study cannot fully explain all the results. Further study is needed to better understand the mechanisms behind the positive effects of winter basking and the negative effects of winter warming on overwintering P. apterus.

Modelling thermal reaction norms for development and viability in Drosophila suzukii under constant, fluctuating and field conditions

Phenological models for insect pests often rely on knowledge of thermal reaction norms. These may differ in shape depending on developmental thermal conditions (e.g. constant vs. fluctuating) and other factors such as life-stages. Here, we conducted an extensive comparative study of the thermal reaction norms for development and viability in the invasive fly, Drosophila suzukii, under constant and fluctuating thermal regimes. Flies, were submitted to 15 different constant temperatures (CT) ranging from 8 to 35 °C. We compared responses under CT with patterns observed under 15 different fluctuating temperature (FT) regimes. We tested several equations for thermal performance curves and compared various models to obtain thermal limits and degree-day estimations. To validate the model's predictions, the phenology was monitored in two artificial field-like conditions and two natural conditions in outdoor cages during spring and winter. Thermal reaction norm for viability from egg to pupa was broader than that from egg to adult. FT conditions yielded a broader thermal breadth for viability than CT, with a performance extended towards the colder side, consistent with our field observations in winter. Models resulting from both CT and FT conditions made accurate predictions of degree-day as long as the temperature remained within the linear part of the developmental rate curve. Under cold artificial and natural winter conditions, a model based on FT data made more accurate predictions. Model based on CT failed to predict adult's emergence in winter. We also document the first record of development and adult emergence throughout winter in D. suzukii. Population dynamics models in D. suzukii are all based on summer phenotype and CT. Accounting for variations between seasonal phenotypes, stages, and thermal conditions (CT vs. FT) could improve the predictive power of the models.

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.

Flies on the rise: acclimation effect on mitochondrial oxidation capacity at normal and high temperatures in Drosophila melanogaster

Increased average temperatures and extreme thermal events (such as heatwaves) brought forth by climate change impose important constraints on aerobic metabolism. Notably, mitochondrial metabolism, which is affected by both long- and short-term temperature changes, has been put forward as an important determinant for thermal tolerance of organisms. This study examined the influence of phenotypic plasticity on metabolic and physiological parameters in Drosophila melanogaster and the link between mitochondrial function and their upper thermal limits. We showed that D. melanogaster acclimated to 15°C have a 0.65°C lower critical thermal maximum (CTmax) compared with those acclimated to 24°C. Drosophila melanogaster acclimated to 15°C exhibited a higher proportion of shorter saturated and monounsaturated fatty acids, concomitant with lower proportions of polyunsaturated fatty acids. No mitochondrial quantitative changes (fractional area and number) were detected between acclimation groups, but changes of mitochondrial oxidation capacities were observed. Specifically, in both 15°C- and 24°C-acclimated flies, complex I-induced respiration was increased when measured between 15 and 24°C, but drastically declined when measured at 40°C. When succinate and glycerol-3-phosphate were added, this decrease was however compensated for in flies acclimated to 24°C, suggesting an important impact of acclimation on mitochondrial function related to thermal tolerance. Our study reveals that the use of oxidative substrates at high temperatures is influenced by acclimation temperature and strongly related to upper thermal tolerance as a difference of 0.65°C in CTmax translates into significant mitochondrial changes.

Strong acclimation effect of temperature and humidity on heat tolerance of the Arctic collembolan Megaphorura arctica

The Arctic is a highly variable environment in which extreme daily and seasonal temperature fluctuations can occur. With climate change, an increase in the occurrence of extreme high temperatures and drought events is expected. While the effects of cold and dehydration stress on polar arthropods are well studied in combination, little is known about how these species respond to the combined effects of heat and dehydration stress. In this paper, we investigated how the heat tolerance of the Arctic collembola Megaphorura arctica is affected by combinations of different temperature and humidity acclimation regimes under controlled laboratory conditions. The effect of acclimation temperature was complex and highly dependent on both acclimation time and temperature, and was found to have a positive, negative or no effect depending on experimental conditions. Further, we found marked effects of the interaction between temperature and humidity on heat tolerance, with lower humidity severely decreasing heat tolerance when the acclimation temperature was increased. This effect was more pronounced with increasing acclimation time. Lastly, the effect of acclimation on heat tolerance under a fluctuating temperature regime was dependent on acclimation temperature and time, as well as humidity levels. Together, these results show that thermal acclimation alone has moderate or no effect on heat tolerance, but that drought events, likely to be more frequent in the future, in combination with high temperature stress can have large negative impacts on heat tolerance of some Arctic arthropods.

Prediction of Potential Distribution of Carposina coreana in China under the Current and Future Climate Change

Carposina coreana is an important pest of Cornus officinalis, distributed in China, Korea, and Japan. In recent years, its damage to C. officinalis has become increasingly serious, causing enormous economic losses in China. This study and prediction of current and future suitable habitats for C. coreana in China can provide an important reference for the monitoring, early warning, prevention, and control of the pest. In this study, the potential distributions of C. coreana in China under current climate and future climate models were predicted using the maximum entropy (MaxEnt) model with ArcGIS software. The distribution point data of C. coreana were screened using the buffer screening method. Nineteen environmental variables were screened using the knife-cut method and variable correlation analysis. The parameters of the MaxEnt model were optimized using the kuenm package in R software. The MaxEnt model, combined with key environmental variables, was used to predict the distribution range of the suitable area for C. coreana under the current (1971-2000) and four future scenarios. The buffer screening method screened data from 41 distribution points that could be used for modeling. The main factors affecting the distribution of C. coreana were precipitation in the driest month (Bio14), precipitation in the warmest quarter (Bio18), precipitation in the coldest quarter (Bio19), the standard deviation of seasonal variation of temperature (Bio4), minimum temperature in the coldest month (Bio6), and average temperature in the coldest quarter (Bio11). The feature class (FC) after the kuenm package optimization was a Q-quadratic T-threshold combination, and the regularization multiplier (RM) was 0.8. The suitable areas for C. coreana under the current climate model were mainly distributed in central China, and the highly suitable areas were distributed in southern Shaanxi, southwestern Henan, and northwestern Hubei. The lowest temperature in the coldest month (Bio6), the average temperature in the coldest quarter (Bio11), and the precipitation in the warmest quarter (Bio18) all had good predictive ability. In future climate scenarios, the boundary of the suitable area for C. coreana in China is expected to shift northward, and thus, most of the future climate scenarios would shift northward.

Evidence of plasticity, but not evolutionary divergence, in the thermal limits of a highly successful urban butterfly

Despite the generally negative impact of urbanization on insect biodiversity, some insect species persist in urban habitats. Understanding the mechanisms underpinning the ability of insects to tolerate urban habitats is critical given the contribution of land-use change to the global insect decline. Compensatory mechanisms such as phenotypic plasticity and evolutionary change in thermal physiological traits could allow urban populations to persist under the altered thermal regimes of urban habitats. It is important to understand the contributions of plasticity and evolution to trait change along urbanization gradients as the two mechanisms operate under different constraints and timescales. Here, we examine the plastic and evolutionary responses of heat and cold tolerance (critical thermal maximum [CTmax] and critical thermal minimum [CTmin]) to warming among populations of the cabbage white butterfly, Pieris rapae, from urban and non-urban (rural) habitats using a two-temperature common garden experiment. Although we expected populations experiencing urban warming to exhibit greater CTmax and diminished CTmin through plastic and evolutionary mechanisms, our study revealed evidence only for plasticity in the expected direction of both thermal tolerance traits. We found no evidence of evolutionary divergence in either heat or cold tolerance, despite each trait showing evolutionary potential. Our results suggest that thermal tolerance plasticity contributes to urban persistence in this system. However, as the magnitude of the plastic response was low and comparable to other insect species, other compensatory mechanisms likely further underpin this species' success in urban habitats.

The Co-occurrence Matrix and the Correlation Network of Phytophagous Insects Are Driven by Abiotic and Biotic Variables: the Case of Canola

Co-occurrence a correlation profiles are driven by different factors (exogenous and endogenous) and drawing a profile of association between species based on co-occurrence, without assessing how these species vary in terms of ecological niche can lead to wrong conclusions. The objective was to determine the co-occurrence and correlation patterns of phytophagous insects in canola crop and to evaluate how these patterns varied according to the crop stage (phenology-biotic) and sowing times (agricultural practice-abiotic). We found that the patterns of co-occurrence and correlation between species were reflections of population variations due to the phenology and sowing times of canola. Variations in the multi-species abundance matrix were influenced by mean air temperature and accumulated rainfall. The main species associated with canola in southern Brazil, in terms of abundance, were P. xylostella, D. speciosa, and N. viridula. These species were mostly negatively associated. When evaluating their population variations, we found that they explore different temporal niches, whether in terms of phenology or sowing times. Finally, we demonstrate empirically that despite being important, association patterns based on co-occurrence and correlation should be interpreted in light of the understanding of patterns of niche exploitation and temporal variation of species.

Machine learning provides insights for spatially explicit pest management strategies by integrating information on population connectivity and habitat use in a key agricultural pest

BACKGROUND

Insect pests have garnered increasing interest because of anthropogenic global change, and their sustainable management requires knowledge of population habitat use and spread patterns. To enhance this knowledge for the prevalent tea pest Empoasca onukii, we utilized a random forest algorithm and a bivariate map to develop and integrate models of its habitat suitability and genetic connectivity across China.

RESULTS

Our modeling revealed heterogeneous spatial patterns in suitability and connectivity despite the common key environmental predictor of isothermality. Analyses indicated that tea cultivation in areas surrounding the Tibetan Plateau and the southern tip of China may be at low risk of population outbreaks because of their predicted low suitability and connectivity. However, regions along the middle and lower reaches of the Yangtze River should consider the high abundance and high recolonization potential of E. onukii, and thus the importance of control measures. Our results also emphasized the need to prevent dispersal from outside regions in the areas north of the Yangtze River and highlighted the effectiveness of internal management efforts in southwestern China and along the southeastern coast. Further projections under future conditions suggested the potential for increased abundance and spread in regions north of the Yangtze River and the southern tip of China, and indicated the importance of long-term monitoring efforts in these areas.

CONCLUSION

These findings highlighted the significance of combining information on habitat use and spread patterns for spatially explicit pest management planning. In addition, the approaches we used have potential applications in the management of other pest systems and the conservation of endangered biological resources. © 2024 Society of Chemical Industry.

Daily temperature fluctuation interacts with the mean temperature to increase the toxicity of a pyrethroid insecticide in a moth

Climate change complicates ecotoxicology studies because species responses to pesticides depend on temperature. Classically illustrated by the effect of constant laboratory temperatures, a recent review revealed that the toxicity of pesticides is also often increased by daily temperature fluctuations. Here, we investigated the combined effects of daily temperature fluctuation and mean temperature on the toxicity of two insecticides in the moth Spodoptera littoralis. Our study tested the toxicity of chlorpyrifos and deltamethrin on larvae of six experimental groups that crossed three treatments of daily temperature fluctuations (0, 5 or 10 °C) and two treatments of mean temperatures (25 or 33 °C). We showed that daily temperature fluctuation increased larval mortality induced by chlorpyrifos and deltamethrin. However, the response differed between the organophosphorus insecticide chlorpyrifos and the pyrethroid insecticide deltamethrin. The increase in chlorpyrifos toxicity by daily temperature fluctuation did not differ between mean temperatures of 25 and 33 °C. Remarkably, the increase in deltamethrin toxicity by daily temperature fluctuation was dependent on the crossed effects of the amplitude of daily fluctuation and mean temperature. This increase in deltamethrin toxicity occurred with a daily fluctuation of only 5 °C for larvae reared at 25 °C and a daily fluctuation of 10 °C in larvae reared at 33 °C. To confidently quantify the responses of insecticide toxicity to temperature, future ecotoxicology studies will have to evaluate the generality of the interaction between the effects of daily temperature fluctuation and mean temperature.

A rapid return to normal: temporal gene expression patterns following cold exposure in the bumble bee Bombus impatiens

Bumble bees are common in cooler climates and many species likely experience periodic exposure to very cold temperatures, but little is known about the temporal dynamics of cold response mechanisms following chill exposure, especially how persistent effects of cold exposure may facilitate tolerance of future events. To investigate molecular processes involved in the temporal response by bumble bees to acute cold exposure, we compared mRNA transcript abundance in Bombus impatiens workers exposed to 0°C for 75 min (inducing chill coma) and control bees maintained at a constant ambient temperature (28°C). We sequenced the 3' end of mRNA transcripts (TagSeq) to quantify gene expression in thoracic tissue of bees at several time points (0, 10, 30, 120 and 720 min) following cold exposure. Significant differences from control bees were only detectable within 30 min after the treatment, with most occurring at the 10 min recovery time point. Genes associated with gluconeogenesis and glycolysis were most notably upregulated, while genes related to lipid and purine metabolism were downregulated. The observed patterns of expression indicate a rapid recovery after chill coma, suggesting an acute differential transcriptional response during recovery from chill coma and return to baseline expression levels within an hour, with no long-term gene expression markers of this cold exposure. Our work highlights the functions and pathways important for acute cold recovery, provides an estimated time frame for recovery from cold exposure in bumble bees, and suggests that cold hardening may be less important for these heterothermic insects.

Warming, but not infection with Borrelia burgdorferi, increases off-host winter activity in the ectoparasite, Ixodes scapularis

Warming winters will change patterns of behaviour in temperate and polar arthropods, but we know little about the drivers of winter activity in animals such as ticks. Any changes in behaviour are likely to arise from a combination of both abiotic (e.g. temperature) and biotic (e.g. infection) drivers, and will have important consequences for survival and species interactions. Blacklegged ticks, Ixodes scapularis, have invaded Atlantic Canada and high proportions (30-50%) are infected with the bacteria causing Lyme disease, Borrelia burgdorferi. Infection is correlated with increased overwintering survival of adult females, and ticks are increasingly active in the winter, but it is unclear if infection is associated with activity. Further, we know little about how temperature drives the frequency of winter activity. Here, we exposed wild-caught, adult, female Ixodes scapularis ticks to three different winter temperature regimes (constant low temperatures, increased warming, and increased warming + variability) to determine the thermal and infection conditions that promote or suppress activity. We used automated behaviour monitors to track daily activity in individual ticks and repeated the study with fresh ticks over three years. Following exposure to winter conditions we determined whether ticks were infected with the bacteria B. burgdorferi and if infection was responsible for any patterns in winter activity. Warming conditions promoted increased activity throughout the overwintering period but infection with B. burgdorferi had no impact on the frequency or overall number of ticks active throughout the winter. Individual ticks varied in their levels of activity throughout the winter, such that some were largely dormant for several weeks, while others were active almost daily; however, we do not yet know the drivers behind this individual variation in behaviour. Overall, warming winters will heighten the risk of tick-host encounters.

Responses of two Anastrepha species' immature stages infesting preferential hosts to different temperature exposures

Anastrepha fraterculus (Wiedemann) and A. obliqua (Macquart) are important pests of fruit crops. In Brazil, these species cause damage to fruit growing in the South (annual average temperature of 20.9 °C) and Northeast (average yearly temperature of 24 °C). We evaluated the effect of temperature on the viability and development time of A. fraterculus and A. obliqua immature stages in their respective preferred hosts, guava (Psidium guajava L., Myrtaceae) and mango (Mangifera indica L., Anacardiaceae). The duration of egg and pupal stages, egg to pre-pupa, and viability of egg and pupal stages under different temperatures (15, 20, 25, 30, and 35 °C) were assessed. For both species, development time decreased with increasing temperature. Viability in the evaluated stages was only observed between 15 and 30 °C. However, the species responded differently to the exposure temperatures (15 and 30 °C), especially in the pupal stage and from egg to pre-pupa. Anastrepha fraterculus showed a lower tolerance to high temperatures, especially in the pupal stage and from egg to pre-pupa, which may explain its lower importance and economic impact in warmer Brazilian regions. Anastrepha obliqua had a lower tolerance at 15 °C, indicating greater adequacy for temperatures above 20 °C, characteristic of Northeast Brazil, suggesting the capacity to spread to cooler areas with rising temperatures.

Predicting the dispersal and invasion dynamics of ambrosia beetles through demographic reconstruction and process-explicit modeling

Evaluating potential routes of invasion of pathogens and vectors of sanitary importance is essential for planning and decision-making at multiple scales. An effective tool are process-explicit models that allow coupling environmental, demographic and dispersal information to evaluate population growth and range dynamics as a function of the abiotic conditions in a region. In this work we simulate multiple dispersal/invasion routes in Mexico that could be taken by ambrosia beetles and a specific symbiont, Harringtonia lauricola, responsible for a severe epiphytic of Lauraceae in North America. We used Xyleborus bispinatus Eichhoff 1868 as a study subject and estimated its demography in the laboratory in a temperature gradient (17, 20, 26, 29, 35 °C), which we then used to parameterize a process-based model to estimate its metapopulation dynamics. The maximum intrinsic growth rate of X. bispinatus is 0.13 with a thermal optimum of 26.2 °C. The models suggest important regions for the establishment and dispersal the states of Veracruz, Chiapas and Oaxaca (high host and secondary vectors diversity), the Isthmus of Tehuantepec (connectivity region), and Michoacán and Jalisco (important avocado plantations). The use of hybrid process-based models is a promising tool to refine the predictions applied to the study of biological invasions and species distributions.

Thermal acclimation uncovers a simple genetic basis of adaptation to high temperature in a cosmopolitan pest

Understanding a population's fitness heterogeneity and genetic basis of thermal adaptation is essential for predicting the responses to global warming. We examined the thermotolerance and genetic adaptation of Plutella xylostella to exposure to hot temperatures. The population fitness parameters of the hot-acclimated DBM strains varied in the thermal environments. Using genome scanning and transcription profiling, we find a number of genes potentially involved in thermal adaptation of DBM. Editing two ABCG transporter genes, PxWhite and PxABCG, confirmed their role in altering cuticle permeability and influencing thermal responses. Our results demonstrate that SNP mutations in genes and changes in gene expression can allow DBM to rapidly adapt to thermal environment. ABCG transporter genes play an important role in thermal adaptation of DBM. This work improves our understanding of genetic adaptation mechanisms of insects to thermal stress and our capacity to predict the effects of rising global temperatures on ectotherms.

Temperature-dependent reproduction of Spodoptera eridania: developing an oviposition model for a novel invasive species

BACKGROUND

Temperature plays a critical role in the development and reproductive process of insects, therefore understanding how insects respond to temperature is vital for comprehending and predicting their population dynamics, particularly when it comes to agricultural pests. Spodoptera eridania Stoll is a polyphagous pest that has recently expanded its distribution beyond its native range. In this study, we assessed the impact of temperature on the reproduction of S. eridania and used the obtained data to develop an oviposition model that could be used to predict egg-laying behavior under field conditions. The reproductive parameters were evaluated at temperatures of 15, 20, 25, 28, and 32 °C.

RESULTS

Temperature had a significant impact on the reproductive parameters examined. Overall, as temperature increased, the pre-oviposition period, oviposition period, and longevity decreased. Total fecundity exhibited a bell-shaped response to temperature, with peak egg-laying observed at 20 and 25 °C. In line with the experimental data, our model predicted higher rates of oviposition between 20 and 26 °C, thus reinforcing that this temperature range may represent the optimal conditions for the reproduction of S. eridania.

CONCLUSION

The findings from our study provide a significant contribution to the understanding of the ecology of an important agricultural pest. The information generated can have practical applications in developing control strategies by enabling the aligning of the timing of control measures with peaks of reproductive activity. © 2023 Society of Chemical Industry.

Thermal limits of survival and reproduction depend on stress duration: A case study of Drosophila suzukii

Studies of ectotherm responses to heat extremes often rely on assessing absolute critical limits for heat coma or death (CTmax), however, such single parameter metrics ignore the importance of stress exposure duration. Furthermore, population persistence may be affected at temperatures considerably below CTmax through decreased reproductive output. Here we investigate the relationship between tolerance duration and severity of heat stress across three ecologically relevant life-history traits (productivity, coma and mortality) using the global agricultural pest Drosophila suzukii. For the first time, we show that for sublethal reproductive traits, tolerance duration decreases exponentially with increasing temperature (R2 > 0.97), thereby extending the Thermal Death Time framework recently developed for mortality and coma. Using field micro-environmental temperatures, we show how thermal stress can lead to considerable reproductive loss at temperatures with limited heat mortality highlighting the importance of including limits to reproductive performance in ecological studies of heat stress vulnerability.

"A comparison of thermal stress response between Drosophila melanogaster and Drosophila pseudoobscura reveals differences between species and sexes"

The environment is changing faster than anticipated due to climate change, making species more vulnerable to its impacts. The level of vulnerability of species is influenced by factors such as the degree and duration of exposure, as well as the physiological sensitivity of organisms to changes in their environments, which has been shown to vary among species, populations, and individuals. Here, we compared physiological changes in fecundity, critical thermalmaximum (CTmax), respiratory quotient (RQ), and DNA damage in ovaries in response to temperature stress in two species of fruit fly, Drosophila melanogaster (25 vs. 29.5 °C) and Drosophila pseudoobscura (20.5 vs. 25 °C). The fecundity of D. melanogaster was more affected by high temperatures when exposed during egg through adult development, while D. pseudoobscura was most significantly affected when exposed to high temperatures exclusively during egg through pupal development. Additionally, D. melanogaster males exhibited a decrease of CTmax under high temperatures, while females showed an increase of CTmax when exposed to high temperatures during egg through adult development. while D. pseudoobscura females and males showed an increased CTmax only when reared at high temperatures during egg through pupae development. Moreover, both species showed an acceleration in oogenesis and an increase in apoptosis due to heat stress. These changes can likely be attributed to key differences in the geographic range, thermal range, development time, and other different factors between these two systems. Through this comparison of variation in physiology and developmental response to thermal stress, we found important differences between species and sexes that suggest future work needs to account for these factors separately in understanding the effects of constant increased temperatures.

Diurnal temperature variation impacts energetics but not reproductive effort across seasons in a temperate dung beetle

Temperature varies on multiple timescales and ectotherms must adjust to these changes to survive. These adjustments may lead to energetic trade-offs between self-maintenance and reproductive investment. However, we know little about how diurnal and seasonal temperature changes impact energy allocation. Here we used a combination of empirical data and modeling of both thermoregulatory behaviors and body temperature to examine potential energetic trade-offs in the dung beetle Onthophagus taurus. Beginning in March 2020, universities and laboratories were officially closed due to the COVID-19 pandemic. We thus performed experiments at a private residence near Knoxville, Tennessee, USA, leveraging the heating, ventilation and air conditioning of the home to manipulate temperature and compare beetle responses to stable indoor temperatures versus variable outdoor temperatures. We collected O. taurus beetles in the early-, mid-, and late-breeding seasons to examine energetics and reproductive output in relation to diurnal and seasonal temperature fluctuations. We recorded the mass of field fresh beetles before and after a 24-h fast and used the resulting change in mass as a proxy for energetic costs of self-maintenance across seasons. To understand the impacts of diurnal fluctuations on energy allocation, we held beetles either indoors or outdoors for 14-day acclimation trials, fed them cow dung, and recorded mass change and reproductive output. Utilizing biophysical models, we integrated individual-level biophysical characteristics, microhabitat-specific performance, respirometry data, and thermoregulatory behaviors to predict temperature-induced changes to the allocation of energy toward survival and reproduction. During 24 h of outdoor fasting, we found that beetles experiencing reduced temperature variation lost more mass than those experiencing greater temperature variation, and this was not affected by season. By contrast, during the 14-day acclimation trials, we found that beetles experiencing reduced temperature variation (i.e., indoors) gained more mass than those experiencing greater temperature variation (i.e., outdoors). This effect may have been driven by shifts in the metabolism of the beetles during acclimation to increased temperature variation. Despite the negative relationship between temperature variation and energetic reserves, the only significant predictor of reproductive output was mean temperature. Taken together, we find that diurnal temperature fluctuations are important for driving energetics, but not reproductive output.

Trehalose 6-phosphate synthase gene rdtps1 contributes to thermal acclimation in Rhyzopertha dominica

BACKGROUND

The lesser grain borer (Rhyzopertha dominica), a worldwide primary pest of stored grain, causes serious economic losses and threatens stored food safety. R. dominica can respond to changes in temperature, especially the adaptability to heat. In this study, transcriptome analysis of R. dominica exposed to different temperatures was performed to elucidate differences in gene expression and the underling molecular mechanism.

RESULTS

Isoform-sequencing generated 17,721,200 raw reads and yielded 20,416 full-length transcripts. A total of 18,880 (92.48%) transcripts were annotated. We extracted RNA from R. dominica reared at 5 °C (cold stress), 15 °C (cold stress), 27 °C (ambient temperature) and 40 °C (heat stress) for RNA-seq. Compared to those of control insects reared at 27 °C, 119, 342, and 875 differentially expressed genes (DEGs) were identified at 5 °C, 15 °C, and 40 °C, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that pathways associated with "fatty acid metabolism", "fatty acid biosynthesis", "AMPK signaling pathway", "neuroactive ligand receptor interaction", and "longevity regulating pathway-multiple species" were significantly enriched. The functional annotation revealed that the genes encoding heat shock proteins (HSPs), fatty acid synthase (FAS), phospholipases (PLA), trehalose transporter (TPST), trehalose 6-phosphate synthase (TPS), and vitellogenin (Vg) were most likely involved in temperature regulation, which was also validated by RT-qPCR. Seven candidate genes (rdhsp1, rdfas1, rdpla1, rdtpst1, rdtps1, rdvg1, and rdP450) were silenced in the RNA interference (RNAi) assay. RNAi of each candidate gene suggested that inhibiting rdtps1 expression significantly decreased the trehalose level and survival rate of R. dominica at 40 °C.

CONCLUSIONS

These results indicated that trehalose contributes to the high temperature resistance of R. dominica. Our study elucidates the molecular mechanisms underlying heat tolerance and provides a potential target for the pest management in R. dominica.

The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis

Climate change involves increases in mean temperature and changes in temperature variability at multiple temporal scales but research rarely considers these temporal scales. The climate variability hypothesis (CVH) provides a conceptual framework for exploring the potential effects of annual scale thermal variability across climatic zones. The CVH predicts ectotherms in temperate regions tolerate a wider range of temperatures than those in tropical regions in response to greater annual variability in temperate regions. However, various other aspects of thermal regimes (e.g. diel variability), organisms' size and taxonomic identity are also hypothesised to influence thermal tolerance. Indeed, high temperatures in the tropics have been proposed as constraining organisms' ability to tolerate a wide range of temperatures, implying that high annual maximum temperatures would be associated with tolerating a narrow range of temperatures. We measured thermal regimes and critical thermal limits (CTmax and CTmin) of freshwater insects in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) along elevation gradients in streams in temperate and tropical regions of eastern Australia and tested the CVH by determining which variables were most correlated with thermal breadth (T br = CTmax - CTmin). Consistent with the CVH, T br tended to increase with increasing annual temperature range. T br also increased with body size and T br was generally wider in Plecoptera than in Ephemeroptera or Trichoptera. We also find some support for a related hypothesis, the climate extreme hypothesis (CEH), particularly for predicting upper thermal limits. We found no evidence that higher annual maximum temperature constrained individuals' abilities to tolerate a wide range of temperatures. The support for the CVH we document suggests that temperate organisms may be able to tolerate wider ranges of temperatures than tropical organisms. There is an urgent need to investigate other aspects of thermal regimes, such as diel temperature cycling and minimum temperature.

Effect of constant and fluctuating low temperature on the survival of Tuta absoluta pupae

Temperature is among the key factors impacting the establishment and spread of invasive pests. The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the major pests attacking Solanaceae plants and is known to possess overwintering capacities. However, the cold hardiness of T. absoluta pupae is poorly documented. In this study, we investigated the effect of constant temperature and stepwise cooling on T. absoluta pupae under laboratory conditions. For this purpose, bioassays on pupal development under constant temperature (5°C) for 30, 60 and 90 days, and stepwise changes in temperature (11, 10 and 8°C; in this order every 30 days), were assessed. We found that exposure to 5°C for 30 and 60 days did not affect the post-cooling emergence time of adults compared to the control. Pupae completed their development after 60 days of cold exposure at 5°C, but more adults emerged after 30 than 60 days. Even though alive pupae were observed after 90 days of cold exposure at 5°C, no adults emerged. External colours of pupae depended on the duration of cold periods, and green pupae obtained after 30 and 60 days were found to be positively correlated with the emergence of adults. When pupae were kept at 11°C for 30 days, 47% emerged, and when the temperature was changed to 10, only 12% of pupae emerged for the period 31-60 days. However, the decrease of the temperature to 8°C yielded no emergence for the period 61-90 days. Our study provides useful information to better understand the population dynamics of overwintering T. absoluta, and to underpin the development of monitoring and control strategies for the pest.

Fitness under high temperatures is overestimated when daily thermal fluctuation is ignored

Experimental studies on the thermal biology of organisms have become crucial to investigate the impact of climate warming. However, most laboratory studies are carried out under constant temperatures and assume a negligible effect from daily fluctuating temperatures. We tested this assumption on multiple fitness traits of the moth Spodoptera littoralis, and a literature review on insects complements this study. Tests on S. littoralis focused on its optimal and maximal critical temperatures by comparing constant and daily fluctuating temperatures (±5 °C) at mean temperatures of 25, 29 and 33 °C. The nine fitness parameters investigated were influenced by mean temperature. The overall effect was a maximal multiplication rate at 29 °C and a marked decrease under the fluctuating regime at 33 °C. Effects of fluctuating temperatures differed between mean temperatures. Developmental and larval survival rates at 33 °C were lower under the fluctuating thermal regime than under a constant temperature. Our literature review also illustrates that ignoring daily fluctuations based on constant temperatures commonly leads to overestimate fitness traits at high temperatures. Overlooking the experimental bias associated with constant temperatures minimizes the expected impact of climate warming on fitness traits.

Phenotypic plasticity of a winter-diapause mechanism copes with the effects of summer global warming in an ectothermic predator

To adapt to changes in temperature, animals tend to invest more energy in thermal tolerance to enhance survival, which can have simultaneous costs on plastic traits. Would a decrease in genetic variability, due to global warming, affect the ability of populations with existing metabolic regulatory mechanisms to cope with extreme temperatures? To address this question, we conducted a series of experiments based on the A1B scenario of global warming, assessing within-population genetic variance in (a) morphological traits, (b) metabolic rate allometries, and (c) survival of a winter-diapausing predator ectotherm. Our study focused on the lacewing species Chrysoperla pallida, using both exogamic and endogamic artificial genetic lines. We discovered that both lines use their winter-diapausing phenotype to adapt to summer extreme temperatures caused by extreme heating conditions, but the exogamic line is prone to express phenotypic plasticity in metabolic scaling, with a trade-off between body size and mandible size, i.e. larger individuals tended to develop smaller mandibles to better survive. These findings highlight the significance of substantial phenotypic plasticity and pre-existing metabolic regulatory mechanisms in enabling ectotherms to cope with potential extreme heating occurring in global warming.

Age determination of Chrysomya megacephala (Diptera: Calliphoridae) using lifespan patterns, gene expression, and pteridine concentration under constant and variable temperatures

Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae), is a blowfly species widely studied in medical, veterinary, and entomological research. Our study examined the impact of constant (15, 20, 25, 30, and 35 °C) and variable (ranging from 21.0 to 25.4 °C, with an average of 23.31 °C) temperatures on the development and larval body length of C. megacephala. Additionally, we analyzed the age of the adult C. megacephala through pteridine content and related metabolic genes analysis. Our findings revealed three distinct growth patterns: isomorphen diagram, isomegalen diagram, and thermal accumulated models. At constant temperatures of 15, 20, 25, 30, and 35 °C, egg-hatching times were 44.5 ± 8.9, 26.7 ± 4.6, 12.6 ± 1.1, 11.0 ± 1.0, and 9.9 ± 1.9 h, respectively, while it was 15.3 ± 5.9 h at variable temperatures. The total development times from oviposition to adult eclosion in C. megacephala required 858.1 ± 69.2, 362.3 ± 5.9, 289.6 ± 17.8, 207.3 ± 9.3, and 184.7 ± 12.1 h at constant temperatures of 15, 20, 25, 30, and 35 °C, respectively. This duration was extended to 282.0 ± 64.1 h under variable temperatures. However, no significant differences were found in hatching times and the total developmental durations between 25 °C and variable temperatures. A developmental threshold temperature (D0) of 9.90 ± 0.77 °C and a thermal summation constant (K) of 4244.0 ± 347.0° hours were ascertained. Pteridine content patterns varied significantly across constant temperatures, but not between 25 °C and variable temperatures. Sex and temperature were identified as the primary factors influencing pteridine levels in the head of C. megacephala. Gene expression associated with pteridine metabolism decreased following adult eclosion, matching with increased pteridine concentration. Further investigations are needed to explore the use of pteridine cofactors for age-grading adult necrophagous flies. These findings provide valuable insights into the lifespan of C. megacephala, thereby offering valuable groundwork for forthcoming investigations and PMImin determination.

Winter Rains Support Butterfly Diversity, but Summer Monsoon Rainfall Drives Post-Monsoon Butterfly Abundance in the Arid Southwest of the US

Butterfly populations are declining worldwide, reflecting our current global biodiversity crisis. Because butterflies are a popular and accurate indicator of insect populations, these declines reflect an even more widespread threat to insects and the food webs upon which they rely. As small ectotherms, insects have a narrow range of habitable conditions; hence, extreme fluctuations and shifts caused by climate change may increase insects' risk of extinction. We evaluated trends of butterfly richness and abundance and their relationship with relevant climate variables in Arizona, U.S.A., using the past 40 years of community science data. We focused on precipitation and temperature as they are known to be influential for insect survival, particularly in arid areas like southwestern U.S.A. We found that preceding winter precipitation is a driver of both spring and summer/fall butterfly richness and spring butterfly abundance. In contrast, summer/fall butterfly abundance was driven by summer monsoon precipitations. The statistically significant declines over the 40-year period were summer/fall butterfly abundance and spring butterfly richness. When controlling for the other variables in the model, there was an average annual 1.81% decline in summer/fall season butterfly abundance and an average annual decline of 2.13 species in the spring season. As climate change continues to negatively impact winter precipitation patterns in this arid region, we anticipate the loss of butterfly species in this region and must consider individual butterfly species trends and additional management and conservation needs.

Regionality in vector control: effect of fluctuating temperature in the susceptibility of Aedes aegypti (Diptera: Culicidae) larvae to Pyriproxyfen

Using Pyriproxyfen in controlling Aedes aegypti shows great potential considering its high competence in low dosages. As an endocrine disruptor, temperature can interfere with its efficiency, related to a decrease in larval emergence inhibition in hotter environments. However, previous studies have been performed at constant temperatures in the laboratory, which may not precisely reflect the environmental conditions in the field. The aim of this study was to assess the effect of the fluctuating temperatures in Pyriproxyfen efficiency on controlling Aedes aegypti larvae. We selected maximum and minimum temperatures from the Brazilian Meteorological Institute database from September to April for cities grouped by five regions. Five fluctuating temperatures (17-26; 20-28.5; 23-32.5; 23-30.5; 19.5-31 °C) were applied to bioassays assessing Pyriproxyfen efficiency in preventing adult emergence in Aedes aegypti larvae in five concentrations. In the lowest temperatures, the most diluted Pyriproxyfen treatment (0.0025 mg/L) was efficient in preventing the emergence of almost thrice the larvae than in the hottest temperatures (61% and 21%, respectively, p value = 0.00015). The concentration that inhibits the emergence of 50% of the population was lower than that preconized by the World Health Organization (0.01 mg/L) in all treatments, except for the hottest temperatures, for which we estimated 0.010 mg/L. We concluded that fluctuating temperatures in laboratory bioassays can provide a more realistic result to integrate the strategies in vector surveillance. For a country with continental proportions such as Brazil, considering regionalities is crucial to the rational use of insecticides.

Higher temperature and daily fluctuations aggravate clothianidin toxicity towards Limnodrilus hoffmeisteri

In nature, aquatic organisms may suffer from chemical pollution, together with thermal stress resulted from global warming. However, limited information is available on the combined effects of pesticide with climate change on aquatic organisms. In this study, the acute toxicity of clothianidin to Limnodrilus hoffmeisteri as well as its effect on the induction of oxidative stress under both constant temperature and daily temperature fluctuation (DTF) regimes was investigated. Results showed that clothianidin exhibited the minimal toxicity to L. hoffmeisteri at 25 °C, which was magnified by both increased or decreased temperatures and 10 °C DTF. At different temperatures (15 °C, 25 °C and 35 °C), clothianidin exposure led to the elevated reactive oxygen species (ROS) levels and activated the antioxidant enzymes to resist against the oxidative stress. However, the antioxidant response induced by clothianidin was overwhelmed at high temperature as evidenced by decreased glutathione (GSH) content. Significant elevation of catalase (CAT) and peroxidase (POD) activities but depletion of GSH was also observed in worms treated with clothianidin under DTF after 24 h. The results indicated that high temperature and DTF could aggravate the clothianidin-induced oxidative stress. Moreover, the critical thermal maximum (CTmax) of the worms decreased with the increasing clothianidin concentrations, suggesting that exposure to clothianidin could reduce the heat tolerance of L. hoffmeisteri. Our work highlights the crucial importance to integrate temperature changes into risk assessment of pesticides under global warming.

Temperature Sensitivity of Fitness Components across Life Cycles Drives Insect Responses to Climate Change

AbstractThermal performance curves (TPCs) are increasingly used as a convenient approach to predict climate change impacts on ectotherms that accounts for organismal thermal sensitivity; however, directly applying TPCs to temperature data to estimate fitness has yielded contrasting predictions depending on assumptions regarding climate variability. We compare direct application of TPCs to an approach integrating TPCs for different fitness components (e.g., per capita birth rate, adult life span) across ectotherm life cycles into a population dynamic model, which we independently validated with census data and applied to hemipteran insect populations across latitude. The population model predicted that climate change will reduce insect fitness more at higher latitudes due to its effects on survival but will reduce net reproductive rate more at lower latitudes due to its effects on fecundity. Directly applying TPCs underestimated climate change impacts on fitness relative to incorporating the TPCs into the population model due to simplifying survival dynamics across the life cycle. The population model predicted that climate change will reduce mean insect density and increase population variability at higher latitudes via reduced survival, despite faster development and a longer activity period. Our study highlights the importance of considering how multiple fitness components respond to climate variability across the life cycle to better understand and anticipate the ecological consequence of climate change.

Temperature alters the toxicological impacts of plant terpenoids on the polyphagous model herbivore Vanessa cardui

Terpenes are a major class of secondary metabolites present in all plants, and long hypothesized to have diversified in response to specific plant-herbivore interactions. Herbivory is a major biotic interaction that plays out across broad temporal and spatial scales that vary dramatically in temperature regimes, both due to climatic variation across geographic locations as well as the effect of seasonality. In addition, there is an emerging understanding that global climate change will continue to alter the temperature regimes of nearly every habitat on Earth over the coming centuries. Regardless of source, variation in temperature may influence herbivory, in particular via changes in the efficacy and impacts of plant defensive chemistry. This study aims to characterize temperature-driven variation in toxicological effects across several structural classes of terpenes in the model herbivore Vanessa cardui, the painted lady butterfly. We observed a general increase in monoterpene toxicity to larvae, pupa, and adults at higher temperatures, as well as an increase in development time as terpene concentration increased. Results obtained from this study yield insights into possible drivers of seasonal variation in plant terpene production as well as inform effects of rising global temperatures on plant-insect interactions. In the context of other known effects of climate change on plant-herbivore interactions like carbon fertilization and compensatory feeding, temperature-driven changes in plant chemical defense efficacy may further complicate the prediction of climate change impacts on the fundamental ecological process of herbivory.

Effects of Temperature and Host Plant on Hedgehog Grain Aphid, Sipha maydis Demographics

The hedgehog grain aphid (HGA), Sipha maydis Passerini (Hemiptera: Aphididae), is a cereal pest in many regions of the world. It was first documented in the United States in 2007, and it has a range that appears to be expanding. Understanding the effects of temperature and the host plant on HGA development, survival, and reproduction is crucial for understanding its population dynamics, potential distribution, and management strategies. In this study, we investigated the effects of different temperatures and host plants on the demographic parameters of HGA and determined the supercooling point (SCP) for their first instars, apterous adults, and winged adults. Our findings revealed that temperatures between 20 °C and 25 °C were optimal for HGA development and reproduction, with parthenogenetic females producing approximately 60 offspring in their lifetimes. However, HGA development was hindered below 10 °C and above 35 °C. The SCP for HGA was similar (mean ± S.E.: -16.280 ± 0.532 °C) among nymphs, apterous adults, and winged adults. We compared the HGA demographics with the demographics of the sorghum aphid (SA), Melanaphis sorghi (Theobald, 1904), on wheat, millet, and three cultivars of sorghum under a constant temperature. The HGA completed its life cycle on all the tested host plants with a similar reproduction, demonstrating a lack of resistance to HGA by a sorghum that is resistant to SA. By expanding our knowledge of host plant- and temperature-dependent development, reproduction, and mortality in S. maydis, we can better predict and manage future HGA populations in small grain crops.

Digestive enzyme activity and macromolecule content in the hemolymph of differentially adapted Lymantria dispar L. populations after short-term increases in ambient temperature

Global, unpredictable temperature increases have strong effects on all organisms, especially insects. Elucidating the effects of short-term temperature increases on midgut digestive enzymes (α-glucosidase, lipase, trypsin, and leucine aminopeptidase - LAP) and metabolic macromolecules in the hemolymph (proteins, lipids, and trehalose) of phytophagous pest larvae of Lymantria dispar is important for general considerations of insect adaptation to a warming climate and potential pest control options. We also wanted to determine whether the different adaptations of L. dispar populations to environmental pollution might affect their ability to cope with heat stress using larvae from the undisturbed, Kosmaj forest and disturbed, Lipovica forest. Heat treatments at 28 °C increased α-glucosidase activity in both larval populations, inhibited LAP activity in larvae from the polluted forest, and had no significant effect on trypsin and lipase activities, regardless of larval origin. The concentration of proteins, lipids, and trehalose in the hemolymph of larvae from the disturbed forest increased, whereas the population from the undisturbed forest showed only an increase in proteins and lipids after the heat treatments. Larval mass was also increased in larvae from the undisturbed forest. Our results suggest a higher sensitivity of digestive enzymes and metabolism to short-term heat stress in L. dispar populations adapted to pollution in their forest habitat, although climate warming is not beneficial even for populations from unpolluted forests. The digestive and metabolic processes of L. dispar larvae are substantially affected by sublethal short-term increases in ambient temperature.