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The relative costs and benefits of thermal acclimation for manipulating field performance of pest insects depend upon a number of factors including which traits are affected and how persistent any trait changes are in different environments. By assessing plastic trait responses of Ceratitis capitata (Mediterranean fruit fly) across three distinct operational environments (laboratory, semi-field, and field), we examined the influence of different thermal acclimation regimes (cool, intermediate [or handling control], and warm) on thermal tolerance traits (chill-coma recovery, heat-knockdown time, critical thermal minimum and critical thermal maximum) and flight performance (mark-release-recapture). Under laboratory conditions, thermal acclimation altered thermal limits in a relatively predictable manner and there was a generally positive effect across all traits assessed, although some traits responded more strongly. By contrast, dispersal-related performance yielded strongly contrasting results depending on the specific operational environment assessed. In semi-field conditions, warm- or cold-acclimated flies were recaptured more often than the control group at cooler ambient conditions suggesting an overall stimulatory influence of thermal variability on low-temperature dispersal. Under field conditions, a different pattern was identified: colder flies were recaptured more in warmer field conditions relative to other treatment groups. This study highlights the trait- and context-specific nature of how thermal acclimation influences traits of thermal performance and tolerance. Consequently, laboratory and semi-field assessments of dispersal may not provide results that extend into the field setting despite the apparent continuum of environmental complexity among them (laboratory < semi-field < field).

Data for the HKD experiment is available here: https://doi.org/10.6084/m9.figshare.21647015.; International audience; 1. Fire is an important cause of disturbance which directly shapes many ecosystems worldwide. While the effect of fire on the distribution and regeneration of plant species has been widely documented, little is known on how phytophagous insects are reacting to these disturbances.2. This study explores the survival strategies of various weevil species, a highly diverse phytophagous beetle group in fire-prone ecosystems of the biodiversity hotspot of the Cape Floristic Region in South Africa. More specifically, we investigated how the lifestyle of species (location of larval development, phenology of adults, and flight ability) correlates with heat tolerance. We hypothesized that wingless species in particular will show better tolerance to heat as they have a limited ability to escape fire rapidly and usually remain hidden in the soil.3. The thermal tolerance of a set of sixteen species with divergent lifestyles and geographic distribution was measured using a standard heat knockdown protocol at 48°C. Respirometry was then performed on the most resistant species using a ramping protocol in order to determine CTmax.4. Our results show that the species tested exhibit high variation in thermal tolerance across taxonomic groups, clustering into three modalities: weak, intermediate, and high tolerance to heat stress. In addition, life history traits (diurnal vs. nocturnal adult activity and location of juvenile stages in plant tissues) likely better explain thermal tolerance at the species level than flight ability or the fire-proneness of ecosystems. Finally, results revealed that some non-flying weevil species are highly heat tolerant with CTmax values reaching up to 50.2 and 51.9°C in species among the Ocladiinae and Brachycerinae subfamilies, respectively.5. Climate change is leading to an increase in the impact and frequency of fires. In this context, this study highlights the diversity of strategies developed by arthropods to escape extreme heat in fire prone ecosystems. Further work is necessary to examine the generality of these patterns across other fire prone ecosystems to better understand behavioural compensation and evolutionary responses, especially given the forecast increases in fire driven by drying and warming associated with climate change.

International audience; Climate warming is considered to be among the most serious of anthropogenic stresses to the environment, because it not only has direct effects on biodiversity, but it also exacerbates the harmful effects of other human-mediated threats. The associated consequences are potentially severe, particularly in terms of threats to species preservation, as well as in the preservation of an array of ecosystem services provided by biodiversity. Among the most affected groups of animals are insects—central components of many ecosystems—for which climate change has pervasive effects from individuals to communities. In this contribution to the scientists' warning series, we summarize the effect of the gradual global surface temperature increase on insects, in terms of physiology, behavior, phenology, distribution, and species interactions, as well as the effect of increased frequency and duration of extreme events such as hot and cold spells, fires, droughts, and floods on these parameters. We warn that, if no action is taken to better understand and reduce the action of climate change on insects, we will drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems. We discuss perspectives on relevant ways to conserve insects in the face of climate change, and we offer several key recommendations on management approaches that can be adopted, on policies that should be pursued, and on the involvement of the general public in the protection effort.

Rapid Evolution of a Cold Stress Cline in Mediterranean Fruit Fly During Northward Range Expansion.

To forecast climate change impacts across habitats or taxa, thermal vulnerability indices (e.g., safety margins and warming tolerances) are growing in popularity. Here, we present their history, context, formulation, and current applications. We highlight discrepancies in terminology and usage, and we draw attention to key assumptions underpinning the main indices and to their ecological and evolutionary relevance. In the process, we flag biases influencing these indices that are not always evaluated. These biases affect both components of index formulations, namely: (i) the characterisation of the thermal environment; and (ii) an organism's physiological and behavioural responses to more frequent and severe warming. Presently, many outstanding questions weaken a thermal vulnerability index approach. We describe ways to validate vulnerability index applications and outline issues to be considered in further developing these indices.

The false codling moth (FCM; Thaumatotibia leucotreta, Meyrick; Lepidoptera: Tortricidae) is a highly polyphagous, major agricultural pest indigenous to sub-Saharan Africa. With growing international trade, there is an increasing concern about introducing this pest into other countries. In South Africa, FCM poses a risk to multiple crops, and is currently suppressed through a combination of chemical, microbial, cultural, augmentative biological control, and the sterile insect technique. Compared with other lepidopteran agricultural pests, such as codling moth Cydia pomonella, genetic and other -omic resources for FCM have not been as well developed and/or not made publicly available to date. The need to develop genomic resources to address questions around insecticide resistance, chemosensory capabilities, and ultimately, develop novel control methods (e.g. gene editing) of this pest is highlighted. In this study, an adult male was sequenced using long-read PacBio Sequel II reads and Illumina NextSeq short reads and assembled using a hybrid assembly pipeline and Pilon error correction. Using the chromosome-level genome assembly of Cy. pomonella, we performed comparative analysis, arranged FCM scaffolds to chromosomes, and investigated genetic variation related to insecticide resistance and chemosensory capabilities. This work provides a platform upon which to build future genomic research on this economically important agricultural pest.

An outbreak of Cacosceles newmannii (Coleoptera: Cerambycidae) was detected for the first time on sugarcane (Saccharum spp.) in 2015 in KwaZulu‐Natal, South Africa. Although primary host plants of this native species remain unknown, these are central to testing hypotheses concerning the outbreak.We hypothesized that this species has undergone a host plant shift (i.e. a feeding association with a novel host plant).We compared δ13C and δ15N ratios of adult beetles retrieved from South African museum collections, collected between 1891 and 2016 (n = 23;'pre‐outbreak'), with samples from infested fields in 2017 (n = 9, 'post‐outbreak') and in 2019 (n = 23, 'post‐outbreak'), as well as diverse, plausible host plants (n = 42 samples across 10 species) from infested fields and surrounding patches of indigenous and commercial forest vegetation. We used Bayesian isotope mixing models to infer the relative contribution of the different plants to the diet of C. newmannii.Pre‐outbreak, C3 plants contributed strongly to the larval diet, whereas post‐outbreak, C4 plants were the largest component of their diet. There was some indication of C4 plants contributing to their diet pre‐outbreak.Our results suggest that the outbreak of this polyphagous beetle was not a dramatic host shift but rather a rapid increase in the proportion of C4 plants already in their diet.We concluded that plants from the families Fabaceae and Poaceae are the most likely host plants of this species. Nevertheless, the drivers of this rapid outbreak on sugarcane remain poorly determined and should be the focus of future research. [ABSTRACT FROM AUTHOR] Copyright of Agricultural & Forest Entomology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biotic interactions can modulate the responses of organisms to environmental stresses, including diet changes. Gut microbes have substantial effects on diverse ecological and evolutionary traits of their hosts, and microbial communities can be highly dynamic within and between individuals in space and time. Modulations of the gut microbiome composition and their potential role in the success of a species to maintain itself in a new environment have been poorly studied to date. Here we examine this question in a large wood-boring beetle Cacosceles newmannii (Cerambycidae), that was recently found thriving on a newly colonized host plant. Using 16S metabarcoding, we assessed the gut bacterial community composition of larvae collected in an infested field and in “common garden” conditions, fed under laboratory-controlled conditions on four either suspected or known hosts (sugarcane, tea tree, wattle, and eucalyptus). We analysed microbiome variation (i.e. diversity and differentiation), measured fitness-related larval growth, and studied host plant lignin and cellulose contents, since their degradation is especially challenging for wood-boring insects. We show that sugarcane seems to be a much more favourable host for larval growth. Bacterial diversity level was the highest in field-collected larvae, whereas lab-reared larvae fed on sugarcane showed a relatively low level of diversity but very specific bacterial variants. Bacterial communities were mainly dominated by Proteobacteria, but were significantly different between sugarcane-fed lab-reared larvae and any other hosts or field-collected larvae. We identified changes in the gut microbiome associated with different hosts over a short time frame, which support the hypothesis of a role of the microbiome in host switches.

International audience; Cold acclimation may enhance low temperature flight ability, and salt loading can alter an insects’ cold tolerance by affecting their ability to maintain ion balance in the cold. Presently however, it remains unclear if dietary salt impacts thermal acclimation of flight ability in insects. Here, we examined the effect of a combination of dietary salt loading (either NaCl or KCl) and low temperature exposure on the flight ability of Drosophila melanogaster at low (15 °C) and benign (optimal, 22 °C) temperatures. Additionally, we determined whether dietary salt supplementation translates into increased K+ and Na+ levels in the bodies of D. melanogaster. Lastly, we determined whether salt supplementation impacts body mass and wing morphology, to ascertain whether any changes in flight ability were potentially driven by flight-related morphometric variation. In control flies, we find that cold acclimation enhances low temperature flight ability over non-acclimated flies confirming the beneficial acclimation hypothesis. By contrast, flies supplemented with KCl that were cold acclimated and tested at a cold temperature had the lowest flight ability, suggesting that excess dietary KCl during development negates the beneficial cold acclimation process that would have otherwise taken place. Overall, the NaCl-supplemented flies and the control group had the greatest flight ability, whilst those fed a KCl-supplemented diet had the lowest. Dietary salt supplementation translated into increased Na+ and K+ concentration in the body tissues of flies, confirming that dietary shifts are reflected in changes in body composition and are not simply regulated out of the body by homeostasis over the course of development. Flies fed with a KCl-supplemented diet tended to be larger with larger wings, whilst those reared on the control or NaCl-supplemented diet were smaller with smaller wings. Additionally, the flies with greater flight ability tended to be smaller and have lower wing loading. In conclusion, dietary salts affected wing morphology as well as ion balance, and dietary KCl seemed to have a detrimental effect on cold acclimation responses of flight ability in D. melanogaster.

Neochetina eichhorniae is the most widely established biocontrol agent on water hyacinth populations around South Africa. However, some N. eichhorniae populations have failed to adequately control their host population, specifically those exposed to cold conditions. The aim of this study was to determine whether two climatically distinct populations of N. eichhorniae in South Africa differ in their low‐temperature physiology, which tests whether local‐climate adaptation has occurred. We estimated weevil CTₘᵢₙ, LLT₅₀, SCP, and SCP mortality using standard approaches. Contrary to expectation based on climatic thermal profiles at the two sites, weevils from the warm locality ((mean ± SE) CTₘᵢₙ = 5.0 °C ± 0.2, LLT₅₀ = −11.3 °C ± 0.03, SCP = −15.8 °C ± 0.6) were able to maintain activity and tolerate colder temperatures than the weevils from the colder site (CTₘᵢₙ = 6.0 °C ± 0.5, LLT₅₀ = −10.1 °C ± 0.1, SCP = −12.9 °C ± 0.8). These contradictory outcomes are likely explained by the poor nutrient quality of the plants at the cold site, driving low‐temperature performance variation that overrode any macroclimate variation among sites. The cold site weevils may also have adapted to survive wide‐temperature variability, rather than perform well under very cold conditions. In contrast, the mass‐reared population of insects from the warm site has likely adapted to the consistent conditions that they experience over many years in confinement.

The fitness consequences of thermal plasticity of functional traits of insects, and the life stages at which these responses manifest, remain a subject of much debate. Here, we examine whether a short-term exposure to cold, medium or warm fluctuating temperature regimes during development (larval or adult) affects adult performance, thermal tolerance and fitness of the globally invasive harlequin ladybird Harmonia axyridis. We found plastic responses of a metric of heat stress resistance—critical thermal maximum—and of preferred body temperature after adult temperature exposure, but not in other traits measured. By contrast, exposure of larval stages resulted in plasticity of adult walking performance (height and breadth of the curve) but not tolerance or preference. We found distinct fitness responses between larval and adult treatments, but a composite fitness index revealed negligible effects on reproductive output. These results suggest that the drivers underlying the plasticity of temperature tolerance and temperature selection are different to those shaping the plasticity of walking speed. By testing specific predictions based on current theory of developmental and reversible plasticity, this study contributes novel data to plastic responses of behaviour, stress resistance and fitness to temperature exposure across life stages and thus, provides insights to the broader evolutionary and ecological significance of these responses.

Understanding the morphological and physiological correlates of competitive behaviours can provide important insights into the ecology of competition, home range size and resource consumption. Here we first estimated and defined sexual dimorphism in a poorly studied African cerambycid species, Cacosceles newmannii (Thomson, 1877). We then assessed morphological and physiological attributes of male beetles in relation to their fighting behaviour. Suites of morphological and energetic measurements were carried out on adult males, the latter before and after male-male interactions. Aggressive behaviour and the outcomes of male fighting trials were assessed under controlled conditions. The species is highly sexually dimorphic in relation to mandible size. During male-male interactions, a continuum of behaviours with an increasing risk of injury and metabolic cost was observed. Grasping was prolonged in males with larger fighting apparatus, who also tended to use more energy during the encounter than males displaying other behaviours. Our results indicate that the mandible size in C. newmannii serves as an honest signal of fighting ability in this species. Additionally, energetic assessments in preparation for fighting, costs during a fight, and persistence of metabolic costs post-fighting may be useful for understanding the relative fitness costs of competition.

Agricultural biosecurity interventions are aimed at minimizing introductions of harmful non-native organisms to new areas via agricultural trade. To prioritize such interventions, historical data on interceptions have been used to elucidate which factors determine the likelihood that a particular import is carrying a harmful organism. Here we use an interception data set of arthropod contaminants recorded on plant imports arriving in South Africa from 2005 to 2019, comprising 13,566 samples inspected for arthropod contaminants, of which 4902 were positive for the presence of at least one arthropod. We tested 29 predictor variables that have previously been used to explain variation in rates of detection and three variables describing possible sources of additional variation and grouped these into six mutually exclusive "factor classes." We used boosted regression trees as a non-parametric stochastic machine-learning method to build models for each factor class and interactions between them. We explored the influence of these variables with data split either randomly or chronologically. While we identified some specific patterns that could be explained post-hoc by historical events, only inspected volumes were reliably correlated with detection of arthropod contaminants across the whole data set. However, inspected volumes could not predict future interceptions of arthropods, which instead relied on contextual factors such as country, crop or year of import. This suggests that, although certain factors may be important in certain circumstances or for particular crops or commodities, there is little general predictive power in the current data. Instead, an idiographic approach would be most beneficial in biosecurity to ascertain the details of why a particular pest arrived on a particular pathway and how it might move (and be stopped) in future.

Females and males have divergent strategies of energy investment, so the thermal preference of each sex in insects may differ because energetic conversion of metabolic reserves is dependent on temperature. We determined the thermal preference of virgin, sexually mature Mediterranean fruit flies, Ceratitis capitata, and found that males preferred a significantly higher temperature (23.8 ± 0.3 °C) than that of females (22.1 ± 0.3 °C). We then tested predictions for the difference in thermal preference related to the energetic demands of reproduction over a range of temperatures. The frequency and duration of calling bouts by male C. capitata were optimal at 26 °C. Mating propensity and latency, and copula duration, were optimal over the range of 22-28 °C. When mating occurred, temperature had little effect on the incidence of sperm storage by females, but there was a notable decline in the number stored at 28 °C. Female lifespan was highest at 18 °C, but lifetime egg production was optimal at 24 °C. These results illustrate temperature-related differences in the reproductive fitness of the sexes in C. capitata, although the optima for male traits align best with their thermal preference. They also support the theoretical prediction that insect thermal preference should be lower than the optimum for fitness.

Acari, as with other small arthropods, are most commonly introduced to new areas as contaminants of agricultural trade. The biosecurity risk of such trade is managed by national and regional biosecurity systems, a chief aim of which is to prevent the introduction of agricultural and environmental pests. However, agricultural contaminants are introduced unintentionally, can occur on any product in a wide range of places, and are often very small in size, which makes them inherently difficult to study, understand, and manage.

Mechanisms aimed at recovering from heat-induced damage are closely associated with the ability of ectotherms to survive exposition to stressful temperatures. Among these mechanisms the respective contribution of autophagy, a ubiquitous stress-responsive catabolic process, has more recently come to light. By increasing the turnover of cellular structures as well as the clearance of long-lived protein and protein aggregates, the induction of autophagy has been linked to increased tolerance to range of abiotic stressors in diverse ectothermic organisms. Since our understanding of the relationship between autophagy and heat-tolerance currently remains limited in insect models, we hypothesized that (1) heat-stress would cause an increase of autophagy inDrosophila melanogastertissues and (2) rapamycin exposure would trigger a detectable autophagic response in flies and increase their heat-tolerance. In line with our hypothesis, we report that flies exposed to heat-stress present signs of protein aggregation and appears to trigger an autophagy-related homoeostatic response as a result. We further show that rapamycin feeding causes the systemic effect associated with TOR inhibition, induces autophagy at least locally in the fly gut, and increase the heat-stress tolerance of individuals. This points toward a likely substantial contribution of this autophagy to cope with stressful temperatures in insects.

Extreme temperature events are increasing in frequency and intensity due to climate change. Such events threaten insects, including pollinators, pests and disease vectors. Insect critical thermal limits can be enhanced through acclimation, yet evidence that plasticity aids survival at extreme temperatures is limited. Here, using meta-analyses across 1374 effect sizes, 74 studies and 102 species, we show that thermal limit plasticity is pervasive but generally weak: per 1 °C rise in acclimation temperature, critical thermal maximum increases by 0.09 °C; and per 1 °C decline, critical thermal minimum decreases by 0.15 °C. Moreover, small but significant publication bias suggests that the magnitude of plasticity is marginally overestimated. We find juvenile insects are more plastic than adults, highlighting that physiological responses of insects vary through ontogeny. Overall, we show critical thermal limit plasticity is likely of limited benefit to insects during extreme climatic events, yet we need more studies in under-represented taxa and geographic regions.

International audience; Historic approaches to understanding biological responses to climate change have viewed climate as something external that happens to organisms. Organisms, however, at least partially influence their own climate experience by moving within local mosaics of microclimates. Such behaviors are increasingly being incorporated into models of species distributions and climate sensitivity. Less attention has focused on how organisms alter microclimates via extended phenotypes: phenotypes that extend beyond the organismal surface, including structures that are induced or built. We argue that predicting the consequences of climate change for organismal performance and fitness will depend on understanding the expression and consequences of extended phenotypes, the microclimatic niches they generate, and the power of plasticity and evolution to shape those niches.

What makes some species successful invaders while others fail, and why some invaders have major impacts in invaded ecosystems are pivotal questions that are attracting major research effort. The increasing availability of high resolution, georeferenced stable isotope landscapes (‘isoscapes’), coupled with the commercialization of stable isotope-enriched tracer molecules and the development of new analytical approaches, is facilitating novel applications of stable isotope techniques in ecology. We can now address ecological questions that were previously intractable. We review and discuss how stable isotope analysis (SIA) can complement fundamental research themes in the study of biological invasions, especially in answering questions relating to the physiological and ecological mechanisms underlying invasion processes and invader impacts. SIA was first used for simply describing the diet of invaders but, more recently, SIA-informed metrics of population and community trophic structure have been advanced. These approaches now permit the comparison of diets across space and time and provide quantitative tools to compare food webs across different stages of invasion. SIA has also been pivotal in quantifying competition for resources between native and non-native species (e.g. competition for food, water, or nutrient use). Specific questions related to modes of dispersal (e.g. origin and distance/direction travelled) and mechanisms of establishment can also be addressed using SIA in diverse taxa. An overarching goal is to highlight examples of recent studies that have used SIA in key areas of invasion ecology and use these to synthesize testable predictions where SIA could be applied to future studies. We conclude by highlighting several paths forward and describing how unresolved challenges in quantifying the rates, impacts, and mechanisms underlying invasions could potentially benefit from the use of SIA.

Bactrocera dorsalis(Hendel) andCeratitis capitata(Wiedemann) are highly polyphagous fruit fly species and important pests of commercial fruit in regions of the world where they are present. In South Africa,B. dorsalisis now established in the north and northeastern parts of the country.B. dorsalisis currently absent in other parts of the country including the Western Cape Province which is an important area for the production of deciduous fruit.C. capitatais widespread in South Africa and is the dominant pest of deciduous fruit. The demographic parameters ofB. dorsalisandC. capitataon four deciduous fruit typesPrunus persica(L.) Batsch,Prunus domesticaL.,Malus domesticaBorkh. andPyrus communisL. were studied to aid in predicting the potential population establishment and growth ofB. dorsalisin a deciduous fruit growing environment. All deciduous fruit types tested were suitable for population persistence of bothB. dorsalisandC. capitata. Development was fastest and survival highest on nectarine for both species.B. dorsalisadults generally lived longer than those ofC. capitata, irrespective of the fruit types that they developed from.B. dorsalishad a higher net reproductive rate (Ro) on all deciduous fruit tested compared toC. capitata. However, the intrinsic rate of population increase was estimated to be higher forC. capitatathan forB. dorsalison all fruit types tested primarily due toC. capitata's faster generation time. Provided abiotic conditions are optimal,B. dorsaliswould be able to establish and grow in deciduous fruit growing areas.

Developmental and adult thermal acclimation can have distinct, even opposite, effects on adult heat resistance in ectotherms. Yet, their relative contribution to heat-hardiness of ectotherms remains unclear despite the broad ecological implications thereof. Furthermore, the deterministic relationship between heat knockdown and recovery from heat stress is poorly understood but significant for establishing causal links between climate variability and population dynamics. Here, using Drosophila melanogaster in a full-factorial experimental design, we assessed the heat tolerance of flies in static stress assays, and document how developmental and adult acclimation interact with a distinct pattern to promote survival to heat stress in adults. We show that warmer adult acclimation is the initial factor enhancing survival to constant stressful high temperatures in flies, but also that the interaction between adult and developmental acclimation becomes gradually more important to ensure survival as the stress persists. This provides an important framework revealing the dynamic interplay between these two forms of acclimation that ultimately enhance thermal tolerance as a function of stress duration. Furthermore, by investigating recovery rates post-stress, we also show that the process of heat-hardening and recovery post-heat knockdown are likely to be based on set of (at least partially) divergent mechanisms. This could bear ecological significance as a trade-off may exist between increasing thermal tolerance and maximizing recovery rates post-stress, constraining population responses when exposed to variable and stressful climatic conditions.

DNA barcoding has been succesfully used for bio-surveillance of forest and agricultural pests in temperate areas, but has few applications in the tropics and particulary in Africa.Cacosceles newmannii(Coleoptera: Cerambycidae) is a Prioninae species that is locally causing extensive damage in commercially-grown sugarcane in the KwaZulu-Natal Province in South Africa. Due to the risk of spread of this species to the rest of southern Africa and to other sugarcane growing regions, clear and easy identification of this pest is critical for monitoring and for phytosanitary services. The genusCacoscelesNewman, 1838 includes four species, most being very similar in morphology. The damaging stage of the species is the larva, which is inherently difficult to distinguish morphologically from other Cerambycidae species. A tool for rapid and reliable identification of this species was needed by plant protection and quarantine agencies to monitor its potential abundance and spread. Here, we provide newly-generated barcodes forC. newmanniithat can be used to reliably identify any life stage, even by non-trained taxonomists. In addition, we compiled a curated DNA barcoding reference library for 70 specimens of 20 named species of Afrotropical Prioninae to evaluate DNA barcoding as a valid tool to identify them. We also assessed the level of deeply conspecific mitochondrial lineages. Sequences were assigned to 42 different Barcode Index Numbers (BINs), 28 of which were new to BOLD. Out of the 20 named species barcoded, 11 (52.4%) had their own unique Barcode Index Number (BIN). Eight species (38.1%) showed multiple BINs with no morphological differentiation. Amongst them,C. newmanniishowed two highly divergent genetic clusters which co-occur sympatrically, but further investigation is required to test whether they could represent new cryptic species.

The establishment success of a population is a function of abiotic and biotic factors and introduction dynamics. Understanding how these factors interact has direct consequences for understanding and managing biological invasions and for applied ecology more generally. Here we use a mesocosm approach to explore how the size of founding populations and the number of introduction events interact with environmental conditions (temperature) to determine the establishment success of laboratory-reared Drosophila melanogaster. We found that temperature played the biggest role in establishment success, eclipsing the role of the other experimental factors when viewed overall. Under optimal temperature conditions propagule pressure was of negligible importance to establishment success. At adverse temperatures, however, establishment success increased with the total founding population size. This effect was considerably stronger at the cold than at the hot extreme. Whether the population was introduced all at once or by increments (changing the number of introduction events) had a negligible global effect. However, once again, a stronger effect of increasing number of introduction events was seen at adverse temperatures, with hot and cold extremes revealing opposite effects: adding flies incrementally decreased their establishment success at the hot extreme, but increased it at the cold extreme. These differing effects at hot and cold thermal extremes implies that different establishment mechanisms are at play at either extreme. These results suggest that the effort required to prevent (or conversely, to facilitate) the establishment of populations varies with the environment in ways that can be complicated but predictable.

Understanding sources of variation in animal thermal limits is critical to forecasting ecological responses to climate change. Here, we estimated upper and lower thermal limits, and their capacity to respond to thermal acclimation, in several species and populations of diving beetles (Dytiscidae) from diverse geographic regions representative of variable climate within South Africa. We also considered ecoregions and latitudinal ranges as potential predictors of thermal limits and the plasticity thereof. For upper thermal limits, species showed significant variation and limited acclimation-related plasticity. Lower thermal limits responded to acclimation in some cases and showed marked variation among species that could be explained by taxonomic affiliation and ecoregion. Limited acclimation ability in the species included in this study suggest plasticity of thermal limits will not be a likely buffer for coping with climate change. From the present results for the Dytiscidae of the region, it appears the group may be particularly susceptible to heat and/or drought and may thus serve as useful indicator species of ecosystem change. Understanding how these climate-related impacts play out at different spatial and temporal scales will have profound implications for conservation management and functional responses, especially important in a region already showing a trend for warming and drying., This research was funded by projects to J.S. Terblanche and CGL2010-15755 to IR and the EEBB of FPI grant BES-2008-007869 to AHG.

Trait–environment interactions have contributed to the remarkable plant radiations in the Cape Floristic Region (CFR) of southern Africa. Whether such interactions have also resulted in the diversification of the invertebrate fauna, independently of direct associations with plants is, however, not clear. One candidate where this may be the case is the unusually diverse Collembola genus Seira. Including 89 species in the CFR, many of which are localised habitat specialists, this genus includes many species inhabiting the warm, dry fynbos shrubland—a habitat atypical of usually desiccation-sensitive Collembola. Here, we investigate whether desiccation tolerance may have contributed to the considerable diversity of Seira in the CFR. First, we demonstrate, by measuring vapour pressure deficits (VPD) of the species’ microhabitats (fynbos shrubland and moister Afrotemperate Forests), that the fynbos shrublands are dry environments (mean ± S.E. maximum VPD 5.2 ± 0.1 kPa) compared with the Afrotemperate Forest patches (0.3 ± 0.02 kPa) during the summer activity period of Seira. Then we show that Seira species living in these shrublands are more desiccation tolerant (mean ± S.E. survival time at 76% relative humidity: 74.3 ± 3.3 h) than their congeners in the cooler, moister Afrotemperate Forests (34.3 ± 2.8 h), and compared with Collembola species globally (3.7 ± 0.2 h). These results, and a previous demonstration of pronounced thermal tolerance in the fynbos shrubland species, suggest that the diversity of Seira in the CFR is at least partly due to pronounced desiccation and thermal tolerance, which has enabled species in the genus to exploit the hot and dry habitats of the CFR.

Metabolic rate, and the flexibility thereof, is a complex trait involving several inter-linked variables that can influence animal energetics, behavior, and ultimately, fitness. Metabolic traits respond readily to ambient temperature variation, in some cases increasing relative or absolute energetic costs, while in other cases, depending on the organism’s metabolic and behavioral responses to changing conditions, resulting in substantial energy savings. To gain insight into the rapid recent emergence of the indigenous South African longhorn beetle Cacosceles newmannii as a crop pest in sugarcane, a better understanding of its metabolic rate, feeding response, digestion times, and aerobic scope is required, in conjunction with any behavioral responses to food availability or limitation thereof. Here, we therefore experimentally determined metabolic rate, estimated indirectly as CO2 production using flow-through respirometry, in starved, fasted, and fed C. newmannii larvae, at 20 °C and 30 °C. We estimated multiple parameters of metabolic rate (starved, standard, active, and maximum metabolic rates) as well as aerobic scope (AS), specific dynamic action (SDA), and the percentage time active during respirometry trials. Additionally, in individuals that showed cyclic or discontinuous gas exchange patterns, we compared rate, volume, and duration of cycles, and how these were influenced by temperature. Standard and active metabolic rate, and AS and SDA were significantly higher in the larvae measured at 30 °C than those measured at 20 °C. By contrast, starved and maximum metabolic rates and percentage time active were unaffected by temperature. At rest and after digestion was complete, 35% of larvae showed cyclic gas exchange at both temperatures; 5% and 15% showed continuous gas exchange at 20 °C and 30 °C respectively, and 10% and 0% showed discontinuous gas exchange at 20 °C and 30 °C respectively. We propose that the ability of C. newmannii larvae to survive extended periods of resource limitation, combined with a rapid ability to process food upon securing resources, even at cooler conditions that would normally suppress digestion in tropical insects, may have contributed to their ability to feed on diverse low energy resources typical of their host plants, and become pests of, and thrive on, a high energy host plant like sugarcane.

Terrestrial insects are responding to ongoing climate change. While these responses have been primarily linked to rising temperatures, insects are sensitive to desiccation, and the impacts of altered precipitation regimes remain relatively unexplored. Here, we develop a mechanistic model of survival and performance responses to both temperature and desiccation stress, focussing on Lepidoptera in Africa, where a general understanding of such responses to climate change is urgently required. We run the model with climate data from general circulation models at daily time intervals under current (2011–2015) and projected future (2046–2050) climate scenarios. We first simulate four hypothetical, but typical, Lepidoptera that vary in thermal tolerance and developmental physiology, and then add a constraint on survival due to desiccation. Including desiccation stress leads to a 68% decline in the species range, in comparison to simulations where only species mortality due to temperature is considered. Furthermore, in response to predicted changes in both temperature and rainfall, species performances and survival are expected to change in a non-uniform manner across the landscape: species’ ranges shift towards coastal regions and into higher latitudes in the southern, but not northern, hemisphere. We validate the model predictions with data from two endemic African Lepidoptera, and find that the model agrees well with their empirical distribution, but note that our model fails to account for range expansion due to water availability unrelated to rainfall (e.g. irrigation). Nonetheless, these final simulations show how the model can be readily applied to insects for which baseline physiological data already exist (or for which appropriate data can be gathered), thereby providing a useful framework with which to explore species responses to future changes in temperature and precipitation.