Thermal plasticity in the invasive south American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Advances in understanding Lepidoptera cold tolerance

Ambient thermal conditions mediate insect growth, development, reproduction, survival, and distribution. With increasingly frequent and severe cold spells, it is critical to determine low-temperature performance and cold tolerances of ecologically and economically essential insect groups to predict their responses to global environmental change. This review covers the cold tolerance strategies of 49 species of Lepidoptera (moths and butterflies), focusing on species that are known as crop pests and crop storage facilities. We synthesize cold tolerance strategies of well-studied species within this order, finding that diapause is a distinctive mechanism that has independently evolved in different genera and families of Lepidoptera. However, the occurrence of diapause in each life stage is specific to the species, and in most studied lepidopteran species, the feeding stage (as larva) is the predominant overwintering stage. We also found that the onset of diapause and the improvement of cold tolerance are interdependent phenomena that typically occur together. Moreover, adopting a cold tolerance strategy is not an inherent, fixed trait and is greatly influenced by a species' geographic distribution and rearing conditions. This review further finds that freeze avoidance rather than freeze tolerance or chill susceptibility is the primary cold tolerance strategy among lepidopteran species. The cold hardiness of lepidopteran insects primarily depends on the accumulation of cryoprotectants and the depression of the supercooling point. We highlight variations in cold tolerance strategies and mechanisms among a subset of Lepidoptera, however, further work is needed to elucidate these strategies for the vast numbers of neglected species and populations to understand broad-scale responses to global change.

DNA methylase 1 influences temperature responses and development in the invasive pest Tuta absoluta

DNA methylase 1 (Dnmt1) is an important regulatory factor associated with biochemical signals required for insect development. It responds to changes in the environment and triggers phenotypic plasticity. Meanwhile, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae)-a destructive invasive pest-can rapidly invade and adapt to different habitats; however, the role of Dnmt1 in this organism has not been elucidated. Accordingly, this study investigates the mechanism(s) underlying the rapid adaptation of Tuta absoluta to temperature stress. Potential regulatory genes were screened via RNAi (RNA interference), and the DNA methylase in Tuta absoluta was cloned by RACE (Rapid amplification of cDNA ends). TaDnmt1 was identified as a potential regulatory gene via bioinformatics; its expression was evaluated in response to temperature stress and during different development stages using real-time polymerase chain reaction. Results revealed that TaDnmt1 participates in hot/cold tolerance, temperature preference and larval development. The full-length cDNA sequence of TaDnmt1 is 3765 bp and encodes a 1254 kDa protein with typical Dnmt1 node-conserved structural features and six conserved DNA-binding active motifs. Moreover, TaDnmt1 expression is significantly altered by temperature stress treatments and within different development stages. Hence, TaDnmt1 likely contributes to temperature responses and organismal development. Furthermore, after treating with double-stranded RNA and exposing Tuta absoluta to 35°C heat shock or -12°C cold shock for 1 h, the survival rate significantly decreases; the preferred temperature is 2°C lower than that of the control group. In addition, the epidermal segments become enlarged and irregularly folded while the surface dries up. This results in a significant increase in larval mortality (57%) and a decrease in pupation (49.3%) and eclosion (50.9%) rates. Hence, TaDnmt1 contributes to temperature stress responses and temperature perception, as well as organismal growth and development, via DNA methylation regulation. These findings suggest that the rapid geographic expansion of T absoluta has been closely associated with TaDnmt1-mediated temperature tolerance. This study advances the research on 'thermos Dnmt' and provides a potential target for RNAi-driven regulation of Tuta absoluta.

A potential trade-off between reproduction and enhancement of thermotolerance in Liriomyza trifolii populations driven by thermal acclimation

The invasive pest, Liriomyza trifolii, poses a significant threat to ornamental and vegetable plants. It spreads rapidly and causes large-scale outbreaks with pronounced thermotolerance. In this study, we developed L. trifolii strains adapted to high temperatures (strains designated 35 and 40); these were generated from a susceptible strain (designated S) by long-term thermal acclimation to 35 °C and 40 °C, respectively. Age-stage, two-sex life tables, thermal preferences, critical thermal limits, knockdown behaviors, eclosion and survival rates as well as expression of genes encoding heat shock proteins (Hsps) were compared for the three strains. Our findings indicated that the thermotolerance of L. trifolii was enhanced after long-term thermal acclimation, which suggested an adaptive plastic response to thermal stress. A trade-off between reproduction and thermotolerance was observed under thermal stress, potentially improving survival of the population and fostering adaptionary changes. Acclimation at 35 °C improved reproductive performance and population density of L. trifolii, particularly by enhancing the fecundity of female adults and accelerating the speed of development. Although the 40 strain exhibited the highest developmental speed and greater thermotolerance, it incurred a larger reproductive cost. This study provides a theoretical framework for monitoring and controlling leafminers and understanding their evolutionary adaptation to environmental changes.

Continent-wide parallel urban evolution of increased heat tolerance in a common moth

Urbanization and its urban-heat-island effect (UHI) have expanding footprints worldwide. The UHI means that urban habitats experience a higher mean and more frequent extreme high temperatures than rural habitats, impacting the ontogeny and resilience of urban biodiversity. However, many organisms occupy different microhabitats during different life stages and thus may experience the UHI differently across their development. While evolutionary changes in heat tolerance in line with the UHI have been demonstrated, it is unknown whether such evolutionary responses can vary across development. Here, using common-garden-reared Chiasmia clathrata moths from urban and rural populations from three European countries, we tested for urban evolution of heat shock tolerance in two life stages: larvae and adults. Our results indicate widespread urban evolution of increased heat tolerance in the adult stage only, suggesting that the UHI may be a stronger selective agent in adults. We also found that the difference in heat tolerance between urban and rural populations was similar to the difference between Mid- and North-European regions, suggesting similarity between adaptation to the UHI and natural, latitudinal temperature variation. Our observations incentivize further research to quantify the impact of these UHI adaptations on fitness during urbanization and climate change, and to check whether life-stage-specific adaptations in heat tolerance are typical of other ectothermic species that manage to survive in urbanized settings.

Meta-analysis reveals less sensitivity of non-native animals than natives to extreme weather worldwide

Extreme weather events (EWEs; for example, heatwaves, cold spells, storms, floods and droughts) and non-native species invasions are two major threats to global biodiversity and are increasing in both frequency and consequences. Here we synthesize 443 studies and apply multilevel mixed-effects metaregression analyses to compare the responses of 187 non-native and 1,852 native animal species across terrestrial, freshwater and marine ecosystems to different types of EWE. Our results show that marine animals, regardless of whether they are non-native or native, are overall insensitive to EWEs, except for negative effects of heatwaves on native mollusks, corals and anemone. By contrast, terrestrial and freshwater non-native animals are only adversely affected by heatwaves and storms, respectively, whereas native animals negatively respond to heatwaves, cold spells and droughts in terrestrial ecosystems and are vulnerable to most EWEs except cold spells in freshwater ecosystems. On average, non-native animals displayed low abundance in terrestrial ecosystems, and decreased body condition and life history traits in freshwater ecosystems, whereas native animals displayed declines in body condition, life history traits, abundance, distribution and recovery in terrestrial ecosystems, and community structure in freshwater ecosystems. By identifying areas with high overlap between EWEs and EWE-tolerant non-native species, we also provide locations where native biodiversity might be adversely affected by their joint effects and where EWEs might facilitate the establishment and/or spread of non-native species under continuing global change.

Predicting the impact of climate change on the potential distribution of the invasive tomato pinworm Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Phthorimaea absoluta (Meyrick) (= Tuta absoluta) (Lepidoptera: Gelechiidae), is the most damaging insect pest threatening the production of tomato and other solanaceous vegetables in many countries. In this study, we predicted the risk of establishment and number of generations for P. absoluta in the current and future climatic conditions under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) of the years 2050 and 2070 using insect life cycle modelling (ILCYM) software. We used a temperature-dependent phenology model to project three risk indices viz., establishment risk index (ERI), generation index (GI), and activity index (AI) based on temperature data. The model projected large suitable areas for P. absoluta establishment in the Southern hemisphere under current and future climatic scenarios, compared to the Northern part. However, the risk of P. absoluta is expected to increase in Europe, USA, Southern Africa, and some parts of Asia in the future. Under current conditions, P. absoluta can complete between 6 and 16 generations per year in suitable areas. However, an increase in GI between 1 and 3 per year is projected for most parts of the world in the future, with an increase in AI between 1 and 4. Our results provide information on the risk of establishment of P. absoluta which could guide decision-makers to develop control strategies adapted for specific agro-ecological zones.

Thermal tolerance responses of the two-spotted stink bug, Bathycoelia distincta (Hemiptera: Pentatomidae), vary with life stage and the sex of adults

Temperature tolerance is an essential component of insect fitness, and its understanding can provide a predictive framework for their distribution and abundance. The two-spotted stink bug, Bathycoelia distincta Distant, is a significant pest of macadamia. The main goal of this study was to investigate the thermal tolerance of B. distincta across different life stages. Thermal tolerance indices investigated included critical thermal maximum (CT_max), critical thermal minimum (CT_min), effects of acclimation on CT_max and CT_min at 20, 25, and 30 °C, and rapid heat hardening (RHH), and rapid cold hardening (RCH). The Kruskal-Wallis test was used to explore the effects of life stage and acclimation on CT_max and CT_min and Generalized Linear Models (GLM) for the probability of survival after pre-exposure to RHH at 41 °C for 2 h and RCH at -8 °C for 2 h. CT_max and CT_min varied significantly between life stages at all acclimation temperatures, but CT_min (3.5 °C) varied more than CT_max (2.1 °C). Higher acclimation temperatures resulted in larger variations between life stages for both CT_max and CT_min. A significant acclimation response was observed for the CT_max of instar 2 (1.7 °C) and CT_min of females (2.7 °C) across acclimation temperatures (20-30 °C). Pre-exposure significantly improved the heat and cold survival probability of instar 2 and the cold survival probability of instar 3 and males. The response between life stages was more variable in RCH than in RHH. Instar 2 appeared to be the most thermally plastic life stage of B. distincta. These results suggest that the thermal plastic traits of B. distincta life stages may enable this pest to survive in temperature regimes under the ongoing climate change, with early life stages (except for instar 2) more temperature sensitive than later life stages.

Estimating the Demographic Parameters of Tuta absoluta (Lepidoptera: Gelechiidae) Using Temperature-Dependent Development Models and Their Validation under Fluctuating Temperature

Simple Summary

Tuta absoluta is an invasive insect pest that has spread widely and established itself in many countries since its first detection in Spain in 2006. The devastating moth originates in South America and attacks tomato and other solanaceous vegetables, leading to huge losses in yield and potential income particularly for small-scale farmers who often lack the resources and knowledge to manage the pest. In most cases, farmers have resorted to the indiscriminate application of broad-spectrum synthetic pesticides, which in most cases are not registered and are often used at high doses. This has resulted in the pest developing resistance to most major classes of pesticides. In addition, the non-selective use of toxic pesticides has resulted in negative effects on the health of users, consumers, and non-target organisms such as pollinators and natural enemies of insect pests. Various tactics aimed at controlling T. absoluta have been developed and are at different stages of adoption by farmers. To ensure that they are effective, sustainable, and friendly to both users and the environment, there is a need for a comprehensive understanding of the pest’s biology and ecology. To this effect, the present study developed models to predict intricate details of the pest’s development, survival, and reproduction using data generated in laboratory studies. Among other important findings, the study reports that temperatures between 20–25 °C are ideal for the development, survival, reproduction, and increase in the population of T. absoluta. These findings are vital in developing strategies in managing the pest, especially in light of global climate change.

Abstract

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an invasive pest that devastates the production of tomatoes and other solanaceous vegetables. Since its trans-Atlantic invasion in 2006, T. absoluta has spread and established in many countries across the Afro-Eurasian Supercontinent, causing huge yield losses. This study aimed to determine the relationship between temperature and the life history traits of T. absoluta and provide the thermal thresholds for development using life cycle modelling. Linear and non-linear models were fitted to life table data collected at five constant temperatures of 15, 20, 25, 30, and 35 °C, with Relative Humidity 70 ± 5% and photoperiod 12L:12D. Another experiment was conducted at fluctuating temperatures to validate the laboratory results. Tuta absoluta completed its life cycle at temperatures between 15 and 35 °C. The development time ranged between 4.0–11 days, 6.3–16.0 days, and 5.4–20.7 days for egg, larva, and pupa, respectively. The lowest thermal threshold was estimated at 8.10, 7.83, and 11.62 °C, respectively for egg, larva, and pupa. While the optimum temperature for T. absoluta immature stages survival and female fecundity were predicted at a temperature range of 21–23 °C. The intrinsic rate of increase (r_m), gross reproductive (GRR), and net reproductive (Ro) rates were significantly higher at temperatures between 20–25 °C. The model validation outcome showed similarities between observed and simulated values for development time, mortality rate, and life table parameters, attesting to the quality of the phenology model. Our results will help in predicting the effect of climate warming on the distribution and population dynamics of T. absoluta. Furthermore, the results could be used to develop management strategies adapted to different agroecological zones.

Water Balance and Desiccation Tolerance of the Invasive South American Tomato Pinworm

Temperature and dehydration stress are two major co-occurring environmental stressors threatening the physiology, biochemistry, and ecology of insects. As such, understanding adaptive responses to desiccation stress is critical for predicting climate change impacts, particularly its influence on insect invasions. Here, we assessed water balance and desiccation resistance of the invasive Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae), and infer how eco-physiology shapes its niche. We measured basal body water and lipid content, water loss rates (WLRs), and desiccation resistance in larvae (second to fourth instars) and adults. Body -water, -lipid, and WLRs significantly varied across life stages. Second instars recorded the lowest while fourth instars exhibited the highest body water and lipid content. Adult body water and lipid content were higher than second and third instars and lower than fourth instars while proportion of body water and lipid contents were highest in adults and second larval instars respectively. Water loss rates were significantly highest in fourth-instar larvae compared to other life stages, but differences among stages were less apparent at longer exposure durations (48 h). Desiccation resistance assays showed that second instars had greatest mortality while fourth-instar larvae and adults were the most desiccation tolerant. Our results show that T. absoluta fourth-instar larvae and adults are the most resilient developmental stages and potentially contribute most to the invasion success of the pest in arid environments. Incorporation of these species-specific eco-physiological traits in predictive models can help refine invasive species potential spread under changing climates.

Molecular Characterization of TRPA Subfamily Genes and Function in Temperature Preference in Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

To reveal the mechanism of temperature preference in Tuta absoluta, one of the top 20 plant pests in the world, we cloned and identified TaTRPA1, TaPain, and TaPyx genes by RACE and bioinformatic analysis, and clarified their expression profiles during different development stages using real-time PCR, and revealed their function in preference temperature by RNAi. The full-length cDNA of TaPain was 3136 bp, with a 2865-bp open reading frame encoding a 259.89-kDa protein; and the partial length cDNA of TaPyx was 2326-bp, with a 2025-bp open reading frame encoding a 193.16-kDa protein. In addition, the expression of TaTRPA1 and TaPyx was significantly lower in larvae than other stages, and it was significantly higher in pupae and newly emerging males for TaPain. After feeding target double-stranded RNA (dsRNA), the preferred temperature decreased 2 °C more than the control group. In conclusion, the results firstly indicated the molecular characterization of TRPA subfamily genes and their key role in temperature perception in T. absoluta, and the study will help us to understand the temperature-sensing mechanism in the pest, and will provide some basis for study of other Lepidoptera insects’ temperature preference. Moreover, it is of great significance in enriching the research progress of “thermos TRP”.

Cold hardiness of the South American tomato pinworm Tuta absoluta (Lepidoptera: Gelechiidae): both larvae and adults are chill-susceptible

BACKGROUND

For many insects, including invasive species, overwintering survival is achieved behaviourally (e.g. through migration) or physiologically by entering diapause, a state of arrested physiological development that may be accompanied with depressed supercooling points (SCPs). Diapause allows in situ adaptation to adverse environmental conditions, providing sufficient parent propagules for insect pest proliferation when optimal conditions resurface. This phenomenon has however not been observed in the invasive South American tomato pinworm Tuta absoluta in its Mediterranean invaded areas. Moreover, no studies have looked at its overwintering survival in sub-Saharan Africa. Here, we thus investigated the cold hardiness of Tuta absoluta larvae and adults to better explain its local overwintering adaptation strategy.

RESULTS

Larval lower lethal temperatures ranged from -1 to -17 °C for 0.5 to 4 h durations. Adults showed lower temperature activity limits than larvae albeit freeze strategy experiments showed neither survived internal freezing. Fasting and dehydration pre-treatment generally depressed SCPs, although asymmetrically, conferring more negative SCPs for larvae. Ramping rates, synonymic to diurnal temperature changes also significantly affected SCPs while, inoculative freezing significantly compromised freezing temperatures in both larvae and adults.

CONCLUSION

Our results suggest that (i) Tuta absoluta larvae and adults are chill-susceptible and may successfully overwinter, (ii) larvae appear more cold hardy than adults and (iii) ecological factors e.g. inoculative freezing, cooling rates, feeding- and hydration-status may affect cold hardiness. These results are important in determining species range limits, population phenology, modelling pest risk status and allows temporal life-stage specific targeting of management strategies.

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) on the "Offensive" in Africa: Prospects for Integrated Management Initiatives

The South American tomato pinworm Tuta absoluta (Meyrick) has aggressively invaded the African continent. Since its first detection in North Africa in Morocco and Tunisia in 2008, it has successfully invaded the entire southern, eastern and western Africa, where it has been on the offensive, causing significant damage to Solanaceous food crops. While control of this prolific invader is primarily based on conventional synthetic pesticides, this form of control is consistently losing societal approval owing to (1) pesticide resistance development and consequential loss of field efficacy; (2) growing public health concerns; (3) environmental contamination and loss of biological diversity and its associated ecological services; and (4) unsustainable costs, particularly for resource-poor African farmers. As such, more ecologically sound pest management strategies, e.g., the use of natural substances (NSs), may offer a more sustainable approach to tackling this offensive. A systematic literature search through digital libraries and online databases (JSTOR, PubMed, Web of Science, SCOPUS and Google Scholar) was conducted using predetermined keywords on T. absoluta, e.g., South American tomato pinworm. We use this to explain the invasion of T. absoluta in Africa, citing mechanisms facilitating African invasion and exploring the potential of its control using diverse biological control agents, natural and low-risk substances. Specifically, we explore how botanicals, entomopathogens, semiochemicals, predators, parasitoids, host plant resistance, sterile insect technique and others have been spatially employed to control T. absoluta and discuss the potential of these control agents in African landscapes using more integrated approaches. We discuss the use of NSs as assets to general insect pest control, some potential associated liabilities and explain the potential use and barriers to adoption in African systems from a legislative, economic, ecological and social standpoint.