Thermal tolerance variations and physiological adjustments in a winter active and a summer active aphid species

Metabolic responses provide insight into interspecific variation in heat tolerance of three co-existing pest aphid species

Global warming leads to an increase in extreme heat events, posing significant challenges for insects. Sitobion avenae, Metopolophium dirhodum and Rhopalosiphum padi are important co-existing aphid species known to cause damage to cereal crops worldwide. The three species differ in thermal tolerance, with R. padi being much more heat tolerant than the other two species. However, it remains unclear whether interspecific variation in heat tolerance is due to differences in metabolic responses to heat stress. Here, we compared their metabolic signatures during and after recovery from the same injury level of heat stress (at 34°C for half and full durations to cause 50% mortality in each species), as well as the identical duration of heat stress. Using quantitative GC-MS, we found that after the same injury level of heat exposure, the three species showed similar changes in most metabolites. However, the heat-tolerant species, R. padi, had higher levels of polyols and amino acids, and uniquely accumulated glycerol. In addition, after the same duration of heat exposure, R. padi maintained a relatively stable metabolic profile, while the less tolerant species showed marked alterations with a shift from aerobic to anaerobic metabolism. We suggest that polyols and amino acids play a pivotal role in protecting R. padi from heat damage, contributing to its superior thermal tolerance. Overall, this comparative metabolomics study provides insight into the relationship between metabolic responses and heat tolerance of co-existing species, which helps understanding of the underlying mechanism of heat tolerance.

Characterizing Three Heat Shock Protein 70 Genes of Aphis gossypii and Their Expression in Response to Temperature and Insecticide Stress

Aphis gossypii is a highly polyphagous pest that causes substantial agricultural damage. Temperature and insecticides are two major abiotic stresses affecting their population abundance. Heat shock proteins play an essential role in cell protection when insects are exposed to environmental stresses. Three ApHsp70 genes were cloned from A. gossypii, and characterized their molecular features and expression profiles in response to temperature and insecticide stress. The deduced amino acid sequences of these proteins exhibited characteristic Hsp70 family signatures, and their tissue-specific expression patterns revealed their highest activity to be in the salivary glands under 35 °C. The temperature inductive assay further indicated that the expression of the three ApHsp70 genes was markedly upregulated under heat stress but not under cold shock. Furthermore, exposure to LC25 and LC50 concentrations of three insecticides triggered the upregulation of these ApHsp70 genes. The RNA interference (RNAi)-mediated suppression of ApHsp68 expression heightened cotton aphid's susceptibility to insecticides (acetamiprid and sulfoxaflor). Moreover, our study found that the sulfoxaflor-resistant strain of A. gossypii (Sul-R) displayed a higher survival rate compared with the sulfoxaflor-sensitive strain (Sul-S) under heat shock conditions. These results suggest that these three ApHsp70 genes play an essential role in response to both heat and insecticide stress.

Glucose influence cold tolerance in the fall armyworm, Spodoptera frugiperda via trehalase gene expression

The fall armyworm (FAW), Spodoptera frugiperda is a cold-sensitive species that overwinters in temperate climates without diapause. Overwintering in insects involves rapid cold hardening (RCH), supported by trehalose (TRE), which serves as an intermediate between glycogen (GLY) and glucose (GLU). However, both GLU and TRE help maintain homeostasis under stress. TRE is hydrolyzed by the enzyme trehalase (Treh) into GLU. This study retrieved Sf-Treh1a, Sf-Treh1b, and Sf-Treh2 from the FAW transcriptome analysis. RNA interference (RNAi) targeting these three Treh genes resulted in significant downregulation of mRNA levels and altered survival rates in RNAi-treated FAW larvae following RCH treatment. High-pressure liquid chromatography (HPLC) quantification of TRE and GLU in treated groups suggests that GLU is an essential component of the hemolymph for survival adaptation to cold conditions in S. frugiperda. This study reveals limited cold adaptability of FAW, as evidenced by lower glucose concentration levels. We found that FAW requires alternative molecules, in conjunction with glucose and trehalose for freeze tolerance and survivability. Our study aims to discover the molecular mechanisms that contribute to freeze tolerance in FAW by exploring the roles of trehalose, glucose, and glycogen.

Molecular and functional characterization of heat-shock protein 70 in Aphis gossypii under thermal and xenobiotic stresses

Aphis gossypii, a globally distributed and economically significant pest of several crops, is known to infest a wide range of host plants. Heat shock proteins (Hsps), acting as molecular chaperones, are essential for the insect's environmental stress responses. The present study investigated the molecular characteristics and expression patterns of AgHsp70, a heat shock protein gene, in Aphis gossypii. Our phylogenetic analysis revealed that AgHsp70 shared high similarity with homologs from other insects, suggesting a conserved function across species. The developmental expression profiles of AgHsp70 in A. gossypii showed that the highest transcript levels were observed in the fourth instar nymphs, while the lowest levels were detected in the third instar nymphs. Heat stress and exposure to four different xenobiotics (2-tridecanone, tannic acid, gossypol, and flupyradifurone (4-[(2,2-difluoroethyl)amino]-2(5H)-furanone)) significantly up-regulated AgHsp70 expression. Knockdown of AgHsp70 using RNAi obviously increased the susceptibility of cotton aphids to 2-tridecanone, gossypol and flupyradifurone. Dual-luciferase reporter assays revealed that gossypol and flupyradifurone significantly enhanced the promoter activity of AgHsp70 at a concentration of 10 mg/L. Furthermore, we identified the transcription factor heat shock factor (HSF) as a regulator of AgHsp70, as silencing AgHSF reduced AgHsp70 expression. Our results shed light on the role of AgHsp70 in xenobiotic adaptation and thermo-tolerance.

The interspecific variations in molecular responses to various doses of heat and cold stress: the case of cereal aphids

Insects are currently subjected to unprecedented thermal stress due to recent increases in the frequency and amplitude of temperature extremes. Understanding molecular responses to thermal stress is critically important to appreciate how species react to thermal stress. Three co-occurring cosmopolitan species are found within the guild of cereal aphids: Sitobion avenae, Ropalosiphum padi and Metopolophium dirhodum. Earlier reports have shown that increasing frequency of temperature extremes causes a shift in dominant species within guilds of cereal aphids by differently altering the population's growth. We hypothesize that a differential molecular response to stress among species may partially explain these changes. Heat shock proteins (HSPs) are molecular chaperones well known to play an important role in protecting against the adverse effects of thermal stress. However, few studies on molecular chaperones have been conducted in cereal aphids. In this study, we compared the heat and cold tolerance between three aphid species by measuring the median lethal time (Lt₅₀) and examined the expression profiles of seven hsp genes after exposures to comparable thermal injury levels and also after same exposure durations. Results showed that R. padi survived comparatively better at high temperatures than the two other species but was more cold-sensitive. Hsp genes were induced more strongly by heat than cold stress. Hsp70A was the most strongly up-regulated gene in response to both heat and cold stress. R. padi had more heat inducible genes and significantly higher mRNA levels of hsp70A, hsp10, hsp60 and hsp90 than the other two species. Hsps ceased to be expressed at 37°C in M. dirhodum and S. avenae while expression was maintained in R. padi. In contrast, M. dirhodum was more cold tolerant and had more cold inducible genes than the others. These results confirm species-specific differences in molecular stress responses and suggest that differences in induced expression of hsps may be related to species' thermal tolerance, thus causing the changes in the relative abundance.

Cold Acclimation and Supercooling Capacity of Agasicles hygrophila Adults

Agasicles hygrophila Selman and Vogt is used in the biological control of the invasive weed Alternanthera philoxeroides (Mart.) Griseb. However, with the northward establishment of A. philoxeroides in China, the weak adaptivity of A. hygrophila to cold weather has resulted in the ineffective control of A. philoxeroides in northern China. Cold acclimation can significantly enhance insect cold tolerance, enabling them to cope with more frequent climate fluctuations. To improve the biological control efficacy of A. hygrophila in cold climates, we compared the effects of rapid cold hardening and acclimation on A. hygrophila under laboratory conditions. On initially transferring adults from 26 to -10 °C for 2 h, mortality reached 80%. However, when pre-exposed to 0 °C for 2 h and then transferred to -10 °C for 2 h, adult mortality was reduced to 36.67%. These findings indicate that cold acclimation can enhance the cold tolerance of A. hygrophila under laboratory conditions. However, the beneficial cold acclimation effects waned after more than 15 min of recovery at 26 °C. Exposure to 15 °C for 24 h or gradual cooling from 0 to -10 °C at 1 °C·min^-1 also induced cold acclimation, indicating that long-term cold and fluctuating cold acclimation are also potentially effective strategies for enhancing low-temperature tolerance.

Highly Efficient Use of Infrared Spectroscopy (ATR-FTIR) to Identify Aphid Species

Aphids are commonly considered to be serious pests for trees, herbaceous and cultivated plants. Recognition and identification of individual species is very difficult and is based mainly on morphological features. The aims of the study were to suggest the possibility of identifying aphids through the use of Fourier-transform infrared (FTIR) spectroscopy, and to determine which absorption peaks are the most useful to separate aphid species. Using FTIR spectroscopy, based on the chemical composition of the body, we were able to distinguish 12 species of aphid. We have shown that using nine distinct peaks corresponding to the molecular vibrations from carbohydrates, lipids, amides I and II, it is possible to accurately identify aphid species with an efficiency of 98%.

Half a century of thermal tolerance studies in springtails (Collembola): A review of metrics, spatial and temporal trends

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Metrics used in thermal tolerance studies in Collembola have diversified over time

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Cold tolerance has been assessed more often than heat tolerance

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Fewer data exist for tropical regions, especially for euedaphic and epedaphic organisms

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Thermal tolerances in Neanuridae are not as well-studied as in the other families

Global changes in soil surface temperatures are altering the abundances and distribution ranges of invertebrate species worldwide, including effects on soil microarthropods such as springtails (Collembola), which are vital for maintaining soil health and providing ecosystem services. Studies of thermal tolerance limits in soil invertebrates have the potential to provide information on demographic responses to climate change and guide assessments of possible impacts on the structure and functioning of ecosystems. Here, we review the state of knowledge of thermal tolerance limits in Collembola. Thermal tolerance metrics have diversified over time, which should be taken into account when conducting large-scale comparative studies. A temporal trend shows that the estimation of ‘Critical Thermal Limits’ (CTL) is becoming more common than investigations of ‘Supercooling Point’ (SCP), despite the latter being the most widely used metric. Indeed, most studies (66%) in Collembola have focused on cold tolerance; fewer have assessed heat tolerance. The majority of thermal tolerance data are from temperate and polar regions, with fewer assessments from tropical and subtropical latitudes. While the hemiedaphic life form represents the majority of records at low latitudes, euedaphic and epedaphic groups remain largely unsampled in these regions compared to the situation in temperate and high latitude regions, where sampling records show a more balanced distribution among the different life forms. Most CTL data are obtained during the warmest period of the year, whereas SCP and ‘Lethal Temperature’ (LT) show more variation in terms of the season when the data were collected. We conclude that more attention should be given to understudied zoogeographical regions across the tropics, as well as certain less-studied clades such as the family Neanuridae, to identify the role of thermal tolerance limits in the redistribution of species under changing climates.

Metabolic Response of Aphid Cinara tujafilina to Cold Stress

Climate changes enable thermophilic insect species to expand their ranges, but also force them to adapt to unfavourable environmental conditions in new habitats. Focusing on Cinara tujafilina, we investigated the metabolic changes in the body of the aphid that enabled it to survive the low temperatures of winter. Using GC–MS analysis, differences in the chemical composition of the aphids in summer and winter were found. The metabolic changes were mainly related to the increased activity of the pathways of carbohydrate metabolism, such as glycolysis and the pentose phosphate pathway; a decrease in tricarboxylic acid cycle (TCA); accumulation of polyols; and increased levels of proline, tyrosine, and fatty acids.