Larval Tolerance Research Articles

Omics Analysis of Odorant-Binding Proteins and Cuticle-Enriched SfruOBP18 Confers Multi-Insecticide Tolerance in Spodoptera frugiperda.

Spodoptera frugiperda is a notorious pest that develops a high resistance to many insecticides. Recently, insect odorant-binding proteins (OBPs) have been proven to participate in insecticide resistance. However, the functional evidence supporting the cross-link between OBPs and insecticide resistance remains unexplored. Here, we identified 50 SfruOBPs from the larval transcriptome and genome. Notably, SfruOBP18 was highly expressed in the larval cuticle and could be induced to upregulate its expression by multi-insecticides. Ligand-binding assays revealed that SfruOBP18 bound strongly with four insecticides; RNAi and insecticide bioassay demonstrated that the knockdown of SfruOBP18 did not affect larval survival and development. However, it can significantly increase the larval susceptibility to multi-insecticides, suggesting an uncommon role of SfruOBP18 in multi-insecticide susceptibility. Our study provides a comprehensive understanding of SfruOBPs and furthermore proves that a larval cuticle-enriched OBP can bind with and confer larval tolerance to multi-insecticides. SfruOBP18 could be a new insecticidal target for controlling Lepidoptera pests.

Genetic diversity and population structure of the semiterrestrial crab Armases benedicti (Brachyura, Sesarmidae) along the North Brazilian coast

Abstract For coastal marine species, gene flow patterns are intricately shaped by environmental factors such as oceanographic currents and river plumes. Despite these natural barriers, pelagic larval duration and salinity tolerance potentially facilitate the movement of individuals, resulting in panmixia. This study utilized Cox1 mtDNA data to conduct population genetics and structure analysis of the semiterrestrial crab Armases benedicti along the North Brazilian coast. The haplotype network displayed a star-like configuration, indicating recent mutation events and confirming minimal genetic structure. While DAPC analysis identified three distinct genetic clusters, limited genetic differentiation and negligible structuring were evident between Amapá, the northmost coastal Brazilian state, and Pará (approx. 400 km from the Amapá sampling site). Maranhão (approx. 600 km from Pará) exhibited higher Fst values in all pairwise comparisons but remained just one mutational step away from other sites. Despite coastal barriers affecting genetic connectivity, our findings suggest that A. benedicti populations demonstrate low genetic differentiation, hinting at the minimal impact of the Amazon plume as a barrier to gene flow, possibly due to the species’ adaptability to brackish environments. However, employing more informative genetic markers and conducting complementary ecological studies on larval salinity tolerance remain crucial for a deeper understanding of Armases population dynamics and adaptive strategies.

Death-Associated LIM-Only Protein Reduces Cry1Ac Toxicity by Sequestration of Cry1Ac Protoxin and Activated Toxin in Helicoverpa armigera.

The extensive use of Bacillus thuringiensis (Bt) in pest management has driven the evolution of pest resistance to Bt toxins, particularly Cry1Ac. Effective management of Bt resistance necessitates a good understanding of which pest proteins interact with Bt toxins. In this study, we screened a Helicoverpa armigera larval midgut cDNA library and captured 208 potential Cry1Ac-interacting proteins. Among these, we further examined the interaction between Cry1Ac and a previously unknown Cry1Ac-interacting protein, HaDALP (H. armigera death-associated LIM-only protein), as well as its role in toxicology. The results revealed that HaDALP specifically binds to both the Cry1Ac protoxin and activated toxin, significantly enhancing cell and larval tolerance to Cry1Ac. Additionally, HaDALP was overexpressed in a Cry1Ac-resistant H. armigera strain. These findings reveal a greater number of Cry1Ac-interacting proteins than previously known and demonstrate, for the first time, that HaDALP reduces Cry1Ac toxicity by sequestering both the protoxin and activated toxin.

Age and calorific restriction impact immature black soldier fly (Diptera: Stratiomyidae) thermal tolerance and preference

Abstract Thermal tolerance and preference are traits commonly considered when mass-producing farmed animals as temperature impacts production. In this study, the impact of age and calorific restriction of immature black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) on associated thermal tolerance and preference was examined. Both age (7-d-old for young larvae and 14-d-old for old larvae) and calorific restriction (led to size differentiation, small for calorific restriction and large for non-restriction) within a given stage influenced thermal tolerance (i.e. KR50) and thermal preference. Results indicate the interaction between age and calorific restriction was significant on both larval and prepupal thermal tolerance but not thermal preference. Median heat tolerance KR50 ranged from 46.4 °C (large, old prepupae) to 48.4 °C (large, young larvae). Median cold tolerance KR50 ranged from 21.6 °C (small, young larvae) to 32.1 °C (small, old larvae). Young larvae preferred median temperatures ∼3.0 °C greater than old larvae. Large larvae preferred median temperatures ∼2.0 °C lower than small larvae. Results from this study indicate ontogeny (i.e. stage of development) and calorific restriction have significant impacts on black soldier fly thermal tolerance and preference. Precise regulation of temperature in an industrial setting is necessary for optimal batch production of the black soldier fly (e.g. survival) and for colony maintenance (e.g. prepupae producing adults and potentially eggs). The same can be said with regards to maintaining consistent age and calorific restriction of immatures produced within each batch as variation in such traits impacts thermal tolerance and preference (e.g. survival to harvest for producing protein or adults for colony) as well. The methods and temperatures used in this study could serve as a foundation for developing standard operating procedures for regulating temperatures experienced by black soldier fly larvae industrially produced.

Storage protein SfSP8 mediates larval starvation tolerance of Spodoptera frugiperda.

Energy homeostasis is vital for insects to survive food shortages. This study investigated the starvation tolerance of Spodoptera frugiperda, which invaded China in 2019, focusing on its storage protein family, crucial for energy balance. 10 storage protein family members were identified and their expression patterns at different development stages and under different starvation stress were analyzed. We used qPCR to evaluate the expression levels of storage protein family members under various larval instars and starvation conditions. We discovered that, among above 10 members, only 2 storage proteins, SfSP8 and SfSP7 showed significant upregulation in response to starvation stress. Notably, SfSP8 upregulated markedly after 24h of fasting, whereas SfSP7 exhibited a delayed response, with significant upregulation observed only after 72h of starvation. Then we significantly reduced the starvation tolerance of larvae through RNAi-mediated knockdown of SfSP8 and also altered the starvation response of SfSP7 from a late to an early activation pattern. Finally, we constructed transgenic Drosophila melanogaster with heterologous overexpressing SfSP8 revealed that the starvation tolerance of the transgenic line was significantly stronger than that of wild-type lines. SfSP8 was the core storage protein member that mediated the starvation tolerance of larvae of S. frugiperda. Our study on the novel function of storage proteins in mediating larval starvation tolerance of S. frugiperda is conducive to understanding the strong colonization of this terrible invasive pest.

High nitrogen application in maize enhances insecticide tolerance of the polyphagous herbivore Spodoptera litura by induction of detoxification enzymes and intensification of cuticle

Nitrogen (N) is one of the most intensively used fertilizers in cropping system and could exert a variety of bottom-up effects on the ecological fitness of herbivores. However, the effects of increased N inputs on insect pesticide tolerance have not been comprehensively understood. Bioassays showed that high N (HN) applied to maize plants significantly increased larval tolerance of Spodoptera litura to multiple insecticides. Activities of detoxification enzymes were significantly higher in the larvae fed on maize plants supplied with HN. RNA-seq analysis showed that numerous GST and cuticle-related genes were induced in the larvae fed on HN maize. RT-qPCR analysis further confirmed four GST genes and larval-specific cuticle gene LCP167. Furthermore, when injected with dsRNA specific to GSTe1, GSTs5, and LCP167, the mortality of larvae treated with methomyl was about 3-fold higher than that of dsGFP-injected larvae. Electron microscope observation showed that cuticle of the larvae fed on HN maize was thicker than the medium level of N. These findings suggest that increased application of N fertilizer enhances insecticide tolerance of lepidopteran pests via induction of detoxification enzymes and intensification of cuticle. Thus, overuse of N fertilizer may increase pest insecticide tolerance and usage of chemical insecticides.

Transcription Factors AhR and ARNT Regulate the Expression of CYP6SX1 and CYP3828A1 Involved in Insecticide Detoxification in Bradysia odoriphaga.

Aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) mediate the responses of adaptive metabolism to various xenobiotics. Here, we found that BoAhR and BoARNT are highly expressed in the midgut of Bradysia odoriphaga larvae. The expression of BoAhR and BoARNT was significantly increased after exposure to imidacloprid and phoxim. The knockdown of BoAhR and BoARNT significantly decreased the expression of CYP6SX1 and CYP3828A1 as well as P450 enzyme activity and caused a significant increase in the sensitivity of larvae to imidacloprid and phoxim. Exposure to β-naphthoflavone (BNF) significantly increased the expression of BoAhR, BoARNT, CYP6SX1, and CYP3828A1 as well as P450 activity and decreased larval sensitivity to imidacloprid and phoxim. Furthermore, CYP6SX1 and CYP3828A1 were significantly induced by imidacloprid and phoxim, and the silencing of these two genes significantly reduced larval tolerance to imidacloprid and phoxim. Taken together, the BoAhR/BoARNT pathway plays key roles in larval tolerance to imidacloprid and phoxim by regulating the expression of CYP6SX1 and CYP3828A1.

Complex parental effects impact variation in larval thermal tolerance in a vertically transmitting coral.

Coral populations must be able to adapt to changing environmental conditions for coral reefs to persist under climate change. The adaptive potential of these organisms is difficult to forecast due to complex interactions between the host animal, dinoflagellate symbionts and the environment. Here we created 26 larval families from six Montipora capitata colonies from a single reef, showing significant, heritable variation in thermal tolerance. Our results indicate that 9.1% of larvae are expected to exhibit four times the thermal tolerance of the general population. Differences in larval thermotolerance were driven mainly by maternal contributions, but we found no evidence that these effects were driven by symbiont identity despite vertical transmission from the dam. We also document no evidence of reproductive incompatibility attributable to symbiont identity. These data demonstrate significant genetic variation within this population which provides the raw material upon which natural selection can act.

Geographic variation in larval cold tolerance and exposure across the invasion front of a widely established forest insect.

Under global climate change, high and low temperature extremes can drive shifts in species distributions. Across the range of a species, thermal tolerance is based on acclimatization, plasticity, and may undergo selection, shaping resilience to temperature stress. In this study, we measured variation in cold temperature tolerance of early instar larvae of an invasive forest insect, Lymantria dispar dispar L. (Lepidoptera: Erebidae), using populations sourced from a range of climates within the current introduced range in the Eastern United States. We tested for population differences in chill coma recovery (CCR) by measuring recovery time following a period of exposure to a nonlethal cold temperature in 2 cold exposure experiments. A 3rd experiment quantified growth responses after CCR to evaluate sublethal effects. Our results indicate that cold tolerance is linked to regional climate, with individuals from populations sourced from colder climates recovering faster from chill coma. While this geographic gradient is seen in many species, detecting this pattern is notable for an introduced species founded from a single point-source introduction. We demonstrate that the cold temperatures used in our experiments occur in nature during cold spells after spring egg hatch, but impacts to growth and survival appear low. We expect that population differences in cold temperature performance manifest more from differences in temperature-dependent growth than acute exposure. Evaluating intraspecific variation in cold tolerance increases our understanding of the role of climatic gradients on the physiology of an invasive species, and contributes to tools for predicting further expansion.

Regulation of CncC in insecticide-induced expression of cytochrome P450 CYP9A14 and CYP6AE11 in Helicoverpa armigera

The expression of many detoxification genes can be regulated by CncC pathway and contributes to insecticide tolerance in insects. Our previous study has demonstrated that the transcripts of CncC and cytochrome P450s (CYP9A14, CYP6AE11) were significantly up-regulated after different insecticides treatment in Helicoverpa armigera. Further study indicated that H2O2, GSH, and MDA contents and antioxidant enzyme activities of H. armigera were enhanced after chlorantraniliprole, cyantraniliprole, indoxacarb, and spinosad exposure. Silencing CncC by RNA interference significantly down-regulated the expression levels of CYP9A14 and CYP6AE11, and increased the susceptibility of dsRNA-injected larvae to λ-cyhalothrin, chlorantraniliprole, and cyantraniliprole. On the contrary, applying CncC agonist curcumin on H. armigera induced the expression of CYP9A14 and CYP6AE11, and enhanced the tolerance of H. armigera to insecticides. Treatment of ROS scavenger N-acetylcysteine on H. armigera reduced the H2O2 content and antioxidant enzyme activities, suppressed the transcripts of CncC, CYP9A14, and CYP6AE11, and decreased the larval tolerance to insecticides. These results demonstrated that the induced-expression of CYP9A14 and CYP6AE11 related with insecticides tolerance in H. armigera was regulated by CncC, which may be activated by ROS generated by insecticides. This study will help to better understand the underlying regulation mechanisms of CncC pathway in H. armigera tolerance to insecticides.

A key evolutionary step determining osmoregulatory ability for freshwater colonisation in early life stage of fish.

Colonisation of freshwater habitats by marine animals is a remarkable evolutionary event that has enriched biodiversity in freshwater ecosystems. The acquisition of the tolerance to hypotonic stress during the early life stages is presumed to be essential for their successful freshwater colonisation, but very little empirical evidence has been obtained to support this idea. This study aimed to comprehend the evolutionary changes of osmoregulatory mechanisms that enhance the larval freshwater tolerance in amphidromous fishes, which typically spend their larval period in marine (ancestral) habitats and the rest of life history stages in freshwater (derived) habitats. We compared the life history patterns and changes in larval survivorship and gene expression depending on salinity among three congeneric marine-originated amphidromous goby species (Gymnogobius), which had been suggested to differ in their larval dependence on freshwater habitats. An otolith microchemical analysis and laboratory-rearing experiment confirmed the presence of freshwater residents only in G. urotaenia and higher larval survivorship of this species in the freshwater condition than the obligate amphidromous G. petschiliensis and G. opperiens. Larval whole-body transcriptome analysis revealed that G. urotaenia from both amphidromous and freshwater-resident populations exhibited the greatest differences in expression levels of several osmoregulatory genes, including aqp3, which is critical for water discharge from their body during early fish development. The present results consistently support the importance of enhanced freshwater tolerance and osmoregulatory plasticity in larval fish to establish freshwater forms, and further identified key candidate genes for larval freshwater adaptation and colonisation in the goby group.

Marine heatwave temperatures enhance larval performance but are meditated by paternal thermal history and inter-individual differences in the purple sea urchin, Strongylocentrotus purpuratus.

Marine heatwave (MHW) events, characterized by periods of anomalous temperatures, are an increasingly prevalent threat to coastal marine ecosystems. Given the seasonal phenology of MHWs, the full extent of their biological consequences may depend on how these thermal stress events align with an organism's reproductive cycle. In organisms with more complex life cycles (e.g., many marine invertebrate species) the alignment of adult and larval environments may be an important factor determining offspring success, setting the stage for MHW events to influence reproduction and development in situ. Here, the influence of MHW-like temperatures on the early development of the California purple sea urchin, Strongylocentrotus purpuratus, were explored within the context of paternal thermal history. Based on temperature data collected during MHW events seen in Southern California from 2014-2020, adult urchins were acclimated to either MHW or non-MHW temperatures for 28days before their sperm was used to produce embryos that were subsequently raised under varying thermal conditions. Once offspring reached an early larval stage, the impact of paternal and offspring environments were assessed on two aspects of offspring performance: larval size and thermal tolerance. Exposure to elevated temperatures during early development resulted in larger, more thermally tolerant larvae, with further influences of paternal identity and thermal history, respectively. The alignment of paternal and offspring exposure to MHW temperatures had additional positive benefits on larval thermal tolerance, but this tolerance significantly decreased when their thermal experience mismatched. As the highest recorded temperatures within past MHW events have occurred during the gametogenesis of many kelp forest benthic marine invertebrate species, such as the purple sea urchin, such parental mediated impacts may represent important drivers of future recruitment and population composition for these species.

Low hypoxia tolerance in larvae of the sardine Sardinops sagax and anchovy Engraulis encrasicolus may limit their stock recovery in the northern Benguela upwelling system

Physiological traits of five key fish species (Cape hake Merluccius spp., pelagic goby Sufflogobius bibarbatus, Cape horse mackerel Trachurus capensis, European anchovy Engraulis encrasicolus and sardine Sardinops sagax) from the northern Benguela upwelling system (NBUS) were compared during their larval stage by measurements of enzymatic activities of key metabolic enzymes (citrate synthase [CS] and pyruvate kinase [PK]). Two distinct age classes (early larvae: 8‒14 days old; late larvae: 22‒29 days old) for each species and from two areas were compared: Terrace Bay (20° S), the main spawning ground of Cape horse mackerel and anchovy, and Kunene (17° S), near the Angola–Benguela frontal zone, where warm and hypoxic water masses intrude into the NBUS. The results revealed significantly higher CS activity in both larval age classes in Cape horse mackerel, anchovy and sardine compared with Cape hake and pelagic goby. Pelagic goby and Cape horse mackerel had significantly higher PK activity compared with Cape hake, anchovy and sardine, apparent in both larval age classes and both areas. Results for anaerobic metabolism indicate higher capacity for pelagic goby and Cape horse mackerel to recover from oxygen debt built up in prey capture and predator escape behaviour and a higher potential for hypoxia tolerance when compared with Cape hake, anchovy and sardine. These results suggest higher survival probability for pelagic goby and Cape horse mackerel compared with the other species under conditions of a shoaling oxygen minimum zone and may explain their current dominance in the NBUS.

Influence of combined temperature and food availability on Peruvian anchovy (Engraulis ringens) early life stages in the northern Humboldt Current system: A modelling approach

In the northern Humboldt Current system (NHCS), the Peruvian anchovy (Engraulis ringens) constitutes the bulk of landings and has a significant socioeconomic contribution. Understanding the impact of environment on the early-life stages of anchovy and further population dynamics remains challenging. Climate variability at a variety of scales modulates currents velocity, temperature and food availability, impacting early-life stages drift, growth and survival. In order to investigate these impacts, we developed Ichthyop-DEB, an individual-based model including larval retention processes and a Dynamic Energy Budget (DEB) bioenergetic module for larval growth. First, we assessed the effect of hydrodynamic simulations horizontal resolution on simulated larval retention patterns using a recruitment age-criterion of 30 days. Then, we evaluated the impact of the following biological processes on simulated larval recruitment patterns: (i) a minimum size-criterion (2 cm), as opposed to a minimum age-criterion (30 days), to be considered as recruited, (ii) the upper larval thermal limit tolerance of the species, for which lab experiments are lacking, and (iii) a constant larval mortality rate. We found that using different resolutions of the hydrodynamic model (10 and 2 km) led to similar simulated larval retention patterns. Retention was highest when spawning occurred in the superficial layer (0–15 m) in austral winter and in the deepest considered layer (30–45 m) in summer. Coupling with the DEB model produced contrasted growth patterns on the continental shelf with a strong month-latitude interaction. Larval recruitment was strongest from 6° to 10° S in austral summer, largely contributing to the average seasonal pattern. Depending on the temperature correction function tested with the bioenergetic module, simulated larval recruitment could also be strong in the northernmost zone (2°–4°S), an area not known for abundant anchovy populations, which suggests a possible thermal growth limitation. Finally, sensitivity tests performed on larval growth limitation by food suggested a deficiency in food supply in the southernmost zone (18°–20°S).

The effect of pollution on the competitive dynamics of Anopheles arabiensis Patton, 1905 and Culex quinquefasciatus Say, 1823 (Diptera: Culicidae)

Culex quinquefasciatus Say, 1823 and Anopheles arabiensis Patton, 1905 (Diptera: Culicidae) are often found breeding in the same water sources and engage in interspecific competition. Although Cx. quinquefasciatus is known to proliferate in a range of polluted environments, the ability of An. arabiensis to proliferate in polluted water has only been reported relatively recently. The effects of pollution and insecticide resistance on this competitive interaction are unknown. This study examined the effect of pollution on the dynamics of the interspecific competition. Three laboratory strains were used in this study: an insecticide susceptible and an insecticide resistant An. arabiensis, and an insecticide resistant Cx. quinquefasciatus. Larval pollutant tolerances of each strain were assessed and compared by determining the lethal concentration at 50% mortality (LC50). The larvae from each strain were exposed to either inorganic fertiliser or copper nitrate, following which eclosion success was assessed. The results showed that the insecticide resistant strains had higher emergence rates when reared in polluted conditions without competition, with the Cx. quinquefasciatus strain showing the highest rate of eclosion. This species also had a higher tolerance for metal pollution than the An. arabiensis strains. The effects of pollutants on oviposition choice were examined. Pollution altered adult oviposition choice. The effect of larval metal exposure had variable effects on the activity of metabolic detoxification enzymes. An insecticide resistant phenotype had greater tolerance to pollutants and possibly developmental advantages based on a variable detoxification response to the pollutant. Pollution can therefore alter interspecific competition dynamics between the malaria vector An. arabiensis and Cx. quinquefasciatus.

Nuclear receptors potentially regulate phytochemical detoxification in Spodoptera litura

Phytochemicals are a class of potential pesticides for pest control. Our previous studies have demonstrated that the development of Spodoptera litura is suppressed by two phytochemicals, flavone and xanthotoxin. Generally, phytochemical is metabolized by insect detoxification enzyme systems. Nuclear receptor (NR) is the ligand-activated transcription factor that involved in the regulation of detoxification gene expressions. To explore how NR responds to phytochemical to mediate detoxification gene expression, in the present study, 19 NRs were firstly identified in S. litura genome. The transcriptional levels of most NRs were significantly induced in the midgut of S. litura larvae after exposure to flavone and xanthotoxin. RNAi-mediated knockdown of FTZF1, EcR, Dsf, and HR3 remarkably reduced the larval tolerance to flavone or xanthotoxin. In addition, many crucial detoxification genes were downregulated by dsNR administrations, which might be responsible for the high sensitivity of S. litura to phytochemicals. Molecular docking indicated that phytochemicals as the potential ligands had high affinity to bind to NRs. This study suggested that NR potentially regulated the transcriptional expression of detoxification genes in response to phytochemical stresses, which partially elucidated the mechanism of extensive host adaptation in S. litura and provided the theoretical evidences for the development of NR-targeted insecticides.

Transcription Factor AhR Regulates Glutathione S-Transferases Conferring Resistance to lambda-Cyhalothrin in Cydia pomonella.

Aryl hydrocarbon receptor (AhR) enhances insect resistance to insecticides by regulating the detoxification network. Our previous studies have confirmed that overexpressions of cytochrome P450 monooxygenases (P450s) and glutathione S-transferases (GSTs) are involved in lambda-cyhalothrin resistance in Cydia pomonella. Here, we report that CpAhR regulates the expression of GST and P450 genes, thus conferring resistance. Expression patterns indicated that the expression of CpAhR was highly induced by lambda-cyhalothrin exposure and upregulated in a lambda-cyhalothrin-resistant population. RNA interference (RNAi) of CpAhR decreases the expression of key resistance-related genes (CpGSTe3, CpCYP9A121, and CpCYP9A122) and the activity of the GST enzyme, reducing the tolerance to lambda-cyhalothrin. Furthermore, β-naphthoflavone, a novel agonist of AhR, was first proven to be effective in increasing CpAhR expression and larval tolerance to lambda-cyhalothrin. These results demonstrate that CpAhR regulates the expression of key detoxifying genes and GST activity, resulting in the development of resistance to lambda-cyhalothrin in C. pomonella.

Desiccation tolerance in larvae of Culex quinquefasciatus Say, 1823 and Anopheles stephensi Liston, 1901 (Diptera: Culicidae): implications for mosquito control

A laboratory assessment of desiccation tolerance in larval stages of mosquitoes Anopheles stephensi Liston, 1901 (Diptera: Culicidae) and Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) was carried out using five temperature levels and three levels of exposure duration as explanatory variables. The increase in the duration of exposure to desiccation from 15 min to 60 min was noted to result in a substantial increase in water loss (in mg) in mosquito larvae. Similarly, the increase in temperature levels was observed to cause larval mortality and a substantial decrease in the emergence of adults. Both the temperature and the duration of exposure to desiccation were found to be influential factors in determining survival and subsequent emergence of adults. Desiccation is a primary factor in determining the survival of mosquito larvae, particularly in the conditions where habitat permanence is uncertain, e.g., in temporary pools and containers serving as mosquito larval habitats. The results of the present study provide a glimpse into the effects of desiccation at varied temperatures and exposure durations on the successful emergence of adults in mosquitoes Cx. quinquefasciatus and An. stephensi. Although primary, the obtained results show that desiccation can be a probable way of regulating the development of mosquito larvae in conditions where the permanence of the habitat for mosquito larvae is uncertain. Further studies on desiccation tolerance may be carried out using different mosquito species that are adapted to temporary pools and containers as sources for breeding.

Contrasting effects of an extended fall period and winter heatwaves on the overwintering fitness of diapausing disease vector, Aedes albopictus

Climate change is expected to dramatically alter autumnal and winter conditions in many temperate regions. However, limited data is available to accurately predict how these changes will impact species’ overwinter survival and post-winter fitness. Here, we determine how a longer, warmer fall period and winter heatwaves affect overwintering fitness and post-winter performance of the invasive mosquito vector, Aedes albopictus. We found that a longer, warmer fall period representative of early entry into diapause did not affect overwinter survival but did lead to reduced post-winter performance for multiple traits. Specifically, larvae that experienced longer, warmer fall conditions as diapause embryos exhibited reduced post-diapause larval starvation tolerance, increased post-diapause larval mortality, and longer post-diapause larval development compared to individuals from the short-fall treatments. These negative post-diapause fitness effects likely resulted from the greater energetic demands and/or damage incurred during the warmer, longer fall period. In contrast, exposure to winter heatwaves increased overwinter survival, possibly by allowing diapausing embryos to escape or repair cold injury. Finally, fall treatment and winter heatwaves had an interactive effect on male development time, while neither treatment impacted pupal mass in either sex. Overall, our results highlight that experiments that fail to measure post-diapause fitness are likely to substantially under-estimate the impacts of climate change on post-winter performance. Additionally, our results emphasize that it is crucial to consider the potentially conflicting effects of different aspects of climate change on a species’ overall overwintering success.

Hundreds of billions of silent outbreaks: A historic outbreak record of the gall midge Schizomyia castanopsisae (Diptera: Cecidomyiidae) on the Izu Islands, Tokyo, Japan, and its potential mechanism

AbstractHerbivore outbreaks cause serious damage to forest trees. In recent decades, outbreaks of the gall midge Schizomyia castanopsisae (Diptera: Cecidomyiidae) inducing inflorescence galls on Castanopsis sieboldii (Fagaceae) occurred in the Izu Islands, Tokyo, Japan. We investigated the gall density on the islands and estimated the larval population on Miyakejima Island. We also surveyed seasonal changes in larval age structure, presence of natural enemies, larval cold tolerance, and thermal effects on the adult emergence. In addition, we conducted molecular phylogenetic analyses of S. castanopsisae populations among different localities. The gall density was particularly high in southern parts (from Miyakejima to Aogashima) of the Izu Islands. The gall midge seemed to have been expanding its range toward northern parts in recent years. On Miyakejima, the larval population was estimated to be approximately 158 and 36 bn in 2017 and 2018, respectively. Parasitoids were not found in the dissection of galls. A cold temperature treatment did not affect the percentage of adult emergence. Developmental zero and thermal constant during the period from larval departure to adult emergence were estimated to be 4.7°C and 588.2°C‐days in males and 7.4°C and 476.2°C‐days in females, and the adults were predicted to emerge in April. Populations in Kyushu were genetically distinct from those in Okinawajima and the Izu Islands, but a common haplotype was found between the latter two localities. These imply that S. castanopsisae on the Izu Islands may be a recent invasion, and the absence of natural enemies causes its outbreaks.