The pine sawyer beetle alters oviposition strategy in response to extreme high temperatures

doi:10.21203/rs.3.rs-3605037/v1

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The pine sawyer beetle alters oviposition strategy in response to extreme high temperatures

https://doi.org/10.21203/rs.3.rs-3605037/v1

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The frequency and intensity of extreme high temperatures (EHTs) are increasing due to the climate warming. Insects have evolved a range of thermotolerance mechanisms to cope with EHTs, whereas there is limited research available on the alteration oviposition strategies under EHTs. This study aims to investigate the impacts of EHTs on the fertility and oviposition strategy of pine sawyer beetle, Monochamus alternatus, a destructive forestry pest. Both male and female adults exhibited a decline in reproductive performance under EHTs. Additionally, M. alternatus females generally laid one egg within one oviposition slit to minimize offspring competition. After EHTs treatments, it was firstly found that the females laid multiple eggs, which was characterized as a novel oviposition strategy. The elicitation of this novel oviposition strategy was negatively correlated with the hatchability of offspring and count of sperms in spermatheca. Furthermore, the hatchability of eggs laid by novel oviposition strategy was significantly lower than that of eggs laid individually. The novel oviposition strategy may help alleviate adverse effects of EHTs on M. alternatus by conserving energy, contributing to the long-term survival of the population. Our findings discovered a novel direction for the behavioral adaptation of insect species in the context of climate warming.

Climate warming

Oviposition strategy

Reproduction

Pine sawyer beetle

Monochamus alternatus is a destructive pine pest, as dominant insect vector of pine wilt disease.
A novel oviposition strategy is all observed under extreme high temperatures in pine sawyer beetle.
The elicitation of novel oviposition strategy was negatively correlated with the vitality of sperms in spermatheca.
Our findings indicates a novel direction for the behavioral adaptation of insects in the context of climate warming.

Global climate change is characterized by a significant rise in extreme high temperatures (EHTs), a trend that is expected to continue in the near future (IPCC 2018). EHTs are defined by meteorologists and ecologists as temperatures that exceed a certain percentile (e.g., the 90th, 95th, or 99th percentile) of temperature distributions (Ma et al. 2021; Arisco et al. 2023). In fact, temperatures exceeding 42°C have been documented in the natural environment in 103 countries (Mherrera 2016). Insects, like other ectotherms, have limited capacity to regulate their own body temperature, making them highly vulnerable to environmental temperatures (Colinet et al. 2015). The increasing frequency and intensity of EHTs are placing insect populations and communities under unprecedented stress. EHTs can directly impact the behavior, survival, development, reproduction, and other biological characteristics of insects, ultimately influencing their population dynamics and distribution range (Ma et al. 2021). Insects have evolved a range of thermotolerance mechanisms to cope with heat stress, including physiological, biochemical, and symbiotic responses, in addition to thermoregulation, ontogenetic variations, and evolutionary adaptations (Harvey et al. 2020).

The reproductive function is known to be highly sensitive to heat, particularly when temperatures exceed the optimal range for insects. Elevated temperatures can hinder the expression and development of behavioral, physiological, and morphological traits that are essential for coordinating reproduction. For example, Zhao et al. (2016) observed that periodic exposure to a 4-hour treatment at 39°C had a negative impact on the fecundity of Agasicles hygrophila. In another study, Sales et al. (2018) discovered that only one-third of sperm cells produced by males of Tribolium castaneum remained viable after a three days treatment at 40°C. In some cases, non-lethal high temperatures can result in transgenerational damage or near-complete sterility in certain insect species. For instance, Zhao et al. (2016) found that when maternal A. hygrophila were exposed to periodic treatments of 39°C for 4 hours, the development time of their offspring's eggs significantly increased. In the case of Cimex lectularius, the hatching success of offspring can drop close to zero when adults are subjected to a 2-week treatment at 38°C (Rukke et al. 2018). Furthermore, (Nguyen et al. 2013) discovered that males of Anisopteromalus calandrae that emerged after a 3-day treatment at 40°C were completely sterile. Despite the well-established understanding of the detrimental effects of high temperatures on insect reproduction, there is limited information available regarding the specific impacts of heat on reproduction based on life stage and sex.

To ensure the protection and adequate food supply for hatching offspring, herbivorous insects employ various oviposition strategies, including laying eggs individually or in small or large batches. These strategies can be influenced by environmental variability. For instance, females of Anastrepha ludens have been observed to adjust the number of eggs per clutch based on host density (Díaz-Fleischer and Aluja 2003). Additionally, physical changes in habitat have been found to impact the oviposition strategies of Odonata species (Calvão et al. 2022). The oviposition strategies of Aedes aegypti, on the other hand, depend on multiple factors such as the physical condition of the oviposition site, the presence of eggs from conspecific females, and the number or size of clutches already present at the site (Chadee 2009). However, there is limited research available on the relationship between insect oviposition strategies and environmental temperature.

Cerambycidae larvae are typically legless and primarily feed inside their host plant. In certain species of Lamiines, larvae may consume conspecific eggs or larvae, or engage in combat resulting in the death of larvae if they encounter each other in the phloem (Hanks and Wang 2017). Consequently, female Cerambycids experiences significant selection pressure in their choice of oviposition sites. The pine sawyer beetle Monochamus alternatus (Coleoptera: Cerambycidae, Lamiines) is a primary vector of the pinewood nematode Bursaphelenchus xylophilus in China and other Asia countries, causing pine wilt disease in millions of hectares of pine forests (Mamiya and Enda 1972; Ye 2019). M. alternatus is typically univoltine, with adults emerging from late spring to summer and exhibiting an average lifespan of nearly seventy days in these regions (Zhao et al. 2008). Upon emergence, the newly developed adults, which have undeveloped eggs and sperm, engage in "maturation feeding" by consuming the bark of pine twigs or other conifers to ensure their survival and sexual maturation (Zhao et al. 2008). Both male and female adults must feed for approximately fifteen days before reaching sexual maturity (Zhao et al. 2008). During oviposition, female M. alternatus beetles chew slits on the surface of the bark using their mandibles, rotate 180°, insert their ovipositors through the center of the wounds, and deposit eggs in the inner bark. In most cases, females lay a single egg or no eggs in the inner bark through a wound, although less frequently they may lay two to three eggs (Togashi K 1981). In China, the most suitable areas for M. alternatus are primarily found in tropical and subtropical zones, where summer temperatures can exceed 40°C (Hu et al. 2013). However, the effects of extreme high temperatures on the reproduction of this insect pest remain largely unknown.

In the current study, we applied repeated periodic high temperatures to simulate the effects of extreme heat events (EHTs) that M. alternatus might experience during the summer. Our aim was to investigate the impact of experimental EHTs on adult fecundity and transgenerational phenotypic traits in M. alternatus, both during the immature and mature adult stages. Furthermore, we aimed to tease apart sex-specific differences in effects of experimental EHTs on reproduction. Additionally, we observed the oviposition strategy of M. alternatus under heat stress by analyzing the distribution pattern of eggs in a single oviposition slit. Finally, we proposed a hypothesis to explain the potential reasons for the change in oviposition strategy observed in M. alternatus under EHTs. The information generated in this study not only contributes to the foundation of research on insect thermotolerance, but also provides critical evidence for assessing the future risks that this insect pest and pine wilt disease pose to agricultural and forestry ecosystems, particularly in the context of climate change.

Insect rearing and collection

The adults of M. alternatus used in this study were taken from a laboratory colony established from fourth-instar larvae collected from dead Pinus massoniana trees infested by B. xylophilus in Nanchang city, Jiangxi Province, China (28°50′45.6″N, 115°32′55.6″E) in Sep. 2020. The M. alternatus larvae, pupae, adults, and eggs were reared as previously described in a photoperiod of 14 hours light: 10 hours dark for adults and a photoperiod of 0 hour light:24 hours dark for eggs, larvae, and pupae at 25 ± 0.5°C with 70 ± 5% relative humidity (RH) (Li et al. 2022).

Extreme high temperature treatments

According to the definition of EHT as the temperature above the 99th percentile of the temperature distributions, the EHT at the aforementioned sampling site in Jul and Aug ranged from 39.1 to 44.9°C. The experimental EHT treatments therefore daily exposed individuals to 42.5°C for 3 hours and then transferred to 25°C for 21 hours with a repetition of sixty days. EHT treatments were applied using a climate chamber (RXZ-436, Ningbo Jiangnan Instrument Factory, Ningbo, China), and the humidity of all treatments was maintained at 70 ± 5%RH with a photoperiod of 14 hours light: 10 hours. One-day-old adults with a body length of 20.00 ± 1.00 mm were reared singly in a plastic box (11.5 cm length × 11.5 cm width × 5 cm height) with a fresh twig of masson pine for 15 days. Upon reaching the reproductive mature stage (16-day-old), ten pairs of beetles as a group were transferred into a net cage (35 cm length × 35 cm width × 40 cm height) with fresh one-year-old masson twigs as food. They were allowed to mate randomly and oviposit on a trunk of masson pine (10 cm diameter, 20 cm height, 1.5 mm bark thickness). The masson twigs and trunks were replaced every two and five days, respectively. Immature adults group (Ima-HS) exposed both immatured females and males (one-day-old) to experimental EHT positioned in the central plane of the incubator. Immature females group (Ima-HF) and males group (Ima-HM) respectively exposed immatured females or males to experimental EHT and mated with same-aged untreated beetles of the opposite sex. Mature adults group (ma-HS) exposed both matured females and males (16-day-old) to experimental EHT positioned in the central plane of the incubator. Mature females group (ma-HF) and males group (ma-HM) respectively exposed matured females or males to experimental EHT and mated with same-aged untreated beetles of the opposite sex. Parallel controls were kept in standard identical conditions but at a daily temperature of 25°C. Figure 1 illustrates the experimental protocols described above. Three replicates (n = 30 pairs) were performed for each treatment.

Reproductive performance

The observation period for assessing reproductive performance covered the age range from 16-day-old to 75-day-old of adult across all the treatments mentioned. During this period, the oviposition slits created by female on the trunks of the mentioned treatments were carefully dissected by precision tweezer, and the eggs within the slit were gently striped by a brush. The number of eggs laid per female and eggs in one slit were recorded daily. The length of eggs were measured by vernier caliper (DL91150, Deli, Ningbo, China). Then, the eggs were individually incubated at 12-well cell culture plates with a moist cotton pad under a photoperiod of 0 h light:24 h dark at 25 ± 0.5°C with 70 ± 5% RH. An incubation period of at least 10 days ensured that all viable larvae had hatched from the fertile eggs. The culture plates were examined every 12 hours to check if the egg hatched successfully. The hatchability and egg developmental period were calculated and recorded. Upon hatching, the neonate larval weight was measured using a precision balance (ME204T, Mettler Toledo, Zurich, Swiss Confederation). In summary, we accessed six metrics related to adult’s reproductive performance: 1) number of eggs per female, 2) egg length, 3) egg hatchability, 4) neonate larval weight, 5) egg developmental period, 6) number of eggs in one slit.

Counts of viable sperms in spermatheca

The spermatheca of 30-day-old mated females in Control, Ima-HS, Ima-HF and Ima-HM groups were respectively dissected on ice. Three spermatheca of the same treatment were mixed in a 1.5 mL tube with 100 µL Grace’s insect buffer (Thermo Fisher, Mas-sachusetts, USA). The sperms were dispersed by stabbing gently with size 0 dissection pins. Sperm cells were stained with 1µl HelixyteTM 14 (100 µmol/L) and 1µl propidium iodide dye (100 µmol/L) darkly under 27 ± 1°C for 5 min. Following incubation, the sperm solutions were then sealed within the slide cavity using a 20 × 20 mm coverslip. The image analysis took place using Zeiss Axiocam and Image J software. Viable sperm heads were imaged in green fluorescence channels.

Data analysis

One-way analysis of variance (ANOVA) and Tukey's multiple comparison analysis were used to evaluate the lifetime fecundity across the various treatments. Significant differences in egg lengths, neonate larval weight and egg developmental periods after EHT treatments were determined using Kruskal‒Wallis ANOVA followed by pairwise comparisons. The egg hatchability across the various treatments and the hatchability between eggs deposited singly and those laid using novel oviposition strategy were determined using chi-square tests followed by Bonferroni correction. Besides, we used Pearson’s correlation analysis to analyze the correlations between P and P2, P1 and P3, and P2 and P3. P1, P2 and P3 respectively mean the egg htachability, count of viable sperms in spermatheca and frequency of novel oviposition strategy (indicating the ratio of number of slits containing multiple egg versus the total number of slits). The linear fits were chosen for curve fitting. All analyses were carried out using SPSS 21.0 (IBM SPSS Statistics, Chicago, IL, USA), and figures were plotted using OriginPro 2022b (OriginLab Inc., Northampton, UK) and chiplot (https://www.chiplot.online/tvbot.html).

EHTs impact on fecundity

As shown in Fig. 2a, the control group of M. alternatus lays 1.40 ± 0.09 eggs per female per day without exhibiting any spawning peak. Likewise, no apparent spawning peaks were observed in any of the heat treatment groups. In control group, the lifetime fecundity reached 85.33 ± 6.12 eggs per female (Fig. 2b). When EHTs occurring in both immature and mature adult stages, the lifetime fecundity had a significantly decrease, with values of 53.25 ± 2.52 and 54.75 ± 0.20 eggs per female, respectively (df = 2,6; F = 22.406; P = 0.002) (Fig. 2b). In terms of fecundity, the impact of EHTs varied between females and males (df = 4,10; F = 17.705; P < 0.001) (Fig. 2b). Specifically, significant reductions in lifetime fecundity were only observed in Ima-HF and ma-HF treatments, with values of 40.13 ± 7.32 and 50.03 ± 3.82 eggs per female, respectively. In contrast, the lifetime fecundity of Ima-HM and ma-HM treatments was comparable to control group. The values were 93.37 ± 7.50 and 103.40 ± 7.49 eggs per female, respectively.

EHTs impact on offspring performance

As displaying in Fig. 3a, the egg length of M. alternatus under normal condition is 3.61 ± 0.01 mm. In ma-HS group, the egg length was dramatically decreased to 3.23 ± 0.01 mm, furthermore, the Ima-HS treatment resulted in a shorter egg length of 3.05 ± 0.01 mm (df = 2; H = 937.131; P < 0.001). Both immature and mature females exposed to EHTs showed a significant reduction in egg length. In contrast, neither immature nor mature males exposed to EHTs had effect on egg length (df = 4; H = 953.275; P < 0.001) (Fig. 3a).

As shown in Fig. 3b, the egg hatchability of control group was 81.61%. However, all the treatments caused a significant decline of egg hatchability to varying degree (df = 6; χ² = 2028.488; P < 0.001). Specifically, the lowest egg hatchability was observed in Ima-HS, ma-HS and Ima-HM treatments, followed by Ima-HF and ma-HF treatments, with the values of 1.34%, 2.91%, 2.26%, 30.03% and 25.76%, respectively. And the ma-HM treatment had a minimal impact on egg hatchability, with the value of 66.27%.

Furthermore, a decrease in neonate larval weight compared to control group was only observed in Ima-HF and ma-HF treatments, with values decreasing from 2.34 ± 0.07 mg to 1.82 ± 0.04 mg and 1.93 ± 0.09 mg respectively (df = 4; H = 1571.557; P < 0.001) (Fig. 3c).

The egg developmental period of various treatments was shown in Fig. 3d. A prolong in egg developmental period compared to control group was observed in the ma-HM, Ima-HF, ma-HF treatments, with values increasing from 5.27 ± 0.03 days to 5.44 ± 0.03 days, 6.06 ± 0.12 days and 5.74 ± 0.08 days, respectively. (df = 4; H = 88.263; P < 0.001).

Oviposition strategy under EHTs

In normal condition, M. alternatus females generally laid one egg within one oviposition slit to minimize offspring competition. After EHTs treatments, it was firstly observed that the females laid two, three, four, five even six eggs within one oviposition slit, which meant that EHTs exposure triggered a novel oviposition strategy, with the characterization of “multiple eggs within one slit”, in M. alternatus (Fig. 4a). The distribution of ratio of egg to oviposition slit of various treatments was shown in Fig. 4b. In the control group, 74.7% of the oviposition slits (n = 1436) chewed by females contained only one egg, while the proportion of slits containing two or more eggs was quiet low, with the value of 0.5%. After exposing males singly, females singly, or both sexes to EHTs, there was a significant increase in the number of eggs in one oviposition slit, except for ma-HM treatment. Specifically, the proportion of slits containing two or more eggs respectively increased to 16.0% (n = 686) and 20.5% (n = 667) in the Ima-HS and ma-HS treatments. The Ima-HF and ma-HF treatments exhibited proportions of oviposition slits containing two or more eggs at 7.0% (n = 539) and 10.7% (n = 619), respectively. The proportion of slits containing two or more eggs was 19.0% (n = 1466) in Ima-HM treatment, whereas this proportion was comparable to that of control group in ma-HM treatment, with the value of 3.0% (n = 1166).

The daily ratio of egg to slit was monitored at ten-day intervals following the maturation of the adults (16-day-old) in order to investigate the relationship between the novel oviposition strategy and the duration of EHTs (Fig. 5). In Ima-HS, Ima-HM, and Ima treatments, where individuals had already exposed to EHTs for fifteen days, “multiple eggs within one slit” was observed immediately upon oviposition, from 16 to 75-day-old. On the other hand, in ma-HS and ma-HF treatments, where individuals had not exposed to EHTs at 16-day-old, “multiple eggs within one slit” was observed after ten days of EHTs, from 26 to 75-day-old.

Relevance of egg hatchability, vitality sperms and novel oviposition strategy

As shown in Fig. 6, there is a positively linear correlation between the egg hatchability and counts of viable sperms in spermatheca across the Control, Ima-HS, Ima-HF and Ima-HM groups, with the values of R² = 0.983 and P = 0.009. Whereas, there is a negatively linear correlation between the egg hatchability and frequency of novel oviposition strategy across these treatments, with the values of R² = 0.952 and P = 0.024. Similarly, there is a negatively linear correlation between the counts of viable sperms in spermatheca and frequency of novel oviposition strategy across these treatments, with the values of R² = 0.981 and P = 0.009. Besides, the hatchability of eggs deposited singly and those laid using novel oviposition strategy in ma-HF treatment was examined. The egg hatchability of the former was 31.68% (n = 584), while none of the latter were able to hatch successfully (n = 195) (χ² = 81.011; P < 0.001).

Our experiments exposed M. alternatus adults to repeated periodic EHTs at a temperature of 42.5°C. Similar cases to researches in other insects, the experimental EHTs not only caused detrimental effects on the fecundity of adults, but also had transgenerational effects on their offspring (Iltis et al. 2020; Sales et al. 2018). Furthermore, we observed the following findings: (i) the reproductive vulnerability to EHTs varied between immature and mature adults, (ii) the impact of EHTs on reproduction varies between sexes, (iii) the experimental EHTs damaged the vitality of sperms in spermatheca, thus triggered a novel oviposition strategy, which might alleviate the detrimental effects of EHTs on M. alternatus.

Stage-specific differences in detrimental effects of EHTs on reproduction

The immature adult stage of M. alternatus had higher sensitivity to EHTs. Specifically, EHTs occurrence in this stage caused a shorter egg length and a lower egg hatchability compared to those when EHTs only occurrence in mature adult stage. Some species of Coleoptera have a complex holometaboliclife cycle that passes through a series of larval stages, a pupal stage where metamorphosis takes place to produce the adult imago, and frequently a final maturing stage to reach the reproductive adult. During the stage of sexual maturation in adults, the reproductive organs undergo further development, while the gametes gradually mature. Ample evidences show that high temperature inflicted major damage to reproductive organs, production and function of gametes. For instance, female Drosophila suzukii that developed at 30°C have smaller ovaries than the untreated group and male flies have less sperm in their testes, and no sperm in their seminal vesicles (Kirk et al. 2019). Experimental heatwave reduces the sperm count, viability, migration through the female and inseminated sperm in female storage of T. castaneum (Sales et al. 2018; Sales et al.2021). Periodically repeated heat events cause to morphological ovarian abnormalities of A.hygrophila ovary (Zhao et al. 2016). Thus, higher sensitivity to EHTs in M. alternatus immature adults might be attributed to the inhibition of sperm production and egg formation in reproductive organs during the immature adult stage. However, further physiological experiments are required to confirm this. The reproductive organs of certain insect species undergo gradual development and maturation during the pupal stage. Previous studies have indicated that subjecting the pupae of these insects to non-lethal high-temperature stress has a greater impact on adult reproductive traits compared to applying heat stress to adult insects (Walsh et al. 2021; Hu et al. 2022). All these findings make it reasonable to hypothesize that the stage at which insect reproductive organs mature is more susceptible to high temperatures in relation to reproductive traits.

Sex-specific differences in detrimental effects of EHTs on reproduction

To better assess the sublethal effects of rising temperatures on insects fertility, it is important to highlight a crucial difference in the way male and female primary reproductive traits respond to thermal stress. In the insect species studied to date, the most emerging pattern is that male gametogenesis appears more sensitive to thermal stress than female gametogenesis. For example, the upper thermal fertility limit of reaches at lower temperatures for males than for females in Drosophila spp (Iossa 2019). Drosophila buzzatii, Drosophila simulans, and Drosophila melanogaster males, but not females, exposed to the same heat stress are infertile, as females mated to unexposed males produce viable offspring (David et al. 2005; Jørgensen et al. 2006). Recent studies in a model insect, T. castaneum, have revealed that males exposed to a single heatwave showed a significant reduction in their ability to sire offspring, more than halving reproductive output following a heatwave, compared with controls. By contrast, female reproductive output is unaffected by the same heatwave conditions (Sales et al. 2018). These phenomena can be explained by the viewpoint that if females are less sensitive than males to heat-induced sterility, they can promote population persistence even at high temperatures (Santos et al. 2023).

However, this was not the case in our study. Although both males and females of M. alternatus exhibited reduced reproductive performance under experimental EHTs, the decrease was more pronounced in females compared to males. EHTs had a negative impact on males in terms of offspring viability, while females experienced declines in fecundity, offspring viability, and quality (specifically, egg length and neonate larval weight) of M. alternatus. It was possible that EHTs have a singular effect on the reproduction of males, leading to a decline in the production and viability of sperm within the testes. In contrast, EHTs had dual effects on the reproduction of females. On one hand, they might have impaired sperm viability within the spermatheca of females. On the other hand, EHTs could have also influenced the formation and development of eggs within the ovaries of females. In all, accounting for these sex-specific differences in thermosensitivity is pivotal to model realistic scenarios for natural populations under heat stress (Iossa 2019). Many researches have claimed that male fertility thermal limits were better predictors of specie’s current distributions and extinction in the laboratory (van Heerwaarden and Sgro 2021). Whereas, we suggested that the fertility thermal limits of females should be also considered as a vital predictor in the future distribution of insect species under climate warming.

Response of oviposition strategy to EHTs

Oviposition strategies of insects can be shaped by host density, the physical condition of oviposition site and the presence of eggs from conspecific females (Calvão et al. 2022; Chadee 2009). In normal condition, M. alternatus females generally laid one egg within one oviposition slit. Whereas, a novel oviposition strategy, characterized as "multiple eggs within one slit", was observed after exposure to experimental EHTs for at least ten days. To our knowledge, this phenomenon that ambient temperatures can elicit a novel oviposition strategy in insects is firstly discovered.

The hypothesis for how EHTs elicit a novel oviposition strategy of M. alternatus is shown in Fig. 7. The novel oviposition strategy of M. alternatus was observed at all the three simulating situations (i: both females and males exposed to experimental EHTs; ii: females singly exposed to experimental EHTs; ii: males singly exposed to experimental EHTs). The elicitation of this novel oviposition strategy was significantly associated with the egg hatchability of offspring and counts of viable sperms in spermatheca following the EHTs treatments. The lower egg hatchability was observed which were accompanied by a higher proportion of novel oviposition strategy. Previously studies have shown that the egg hatchability was highly dependent on the vitality of sperms (Sales et al. 2017; Sales et al. 2018). Similarly we found there was a negative relationship between the egg hatchability and counts of viable sperms in spermatheca of M. alternatus. Additionally, we observed that none of the eggs laid using the novel oviposition strategy were able to successfully hatch, whereas the hatchability of eggs laid using the original oviposition strategy was close to one-third in the experimental EHTs treatment groups. The vitality of sperm within the spermatheca of females in M. alternatus could be compromised in all three situations mentioned earlier. Consequently, it was highly likely that females sense the vitality of sperm within the spermatheca through some signaling pathways, which then influenced their oviposition choice. Specifically, when females detected the presence of damaged sperm in their spermatheca caused by EHTs, they modified their oviposition strategy by choosing to deposit multiple non-viable eggs within a single slit.

Over thirty minutes is required for the integrated oviposition behavior of M. alternatus, which consists of three steps: chewing slits on the surface of the bark, rotating 180°, and depositing a single egg using their ovipositors in the inner bark (Togashi K 1981). This suggests that the oviposition behavior of M. alternatus is highly energy-intensive. Heat stress could result in excessive energy costs, potentially leading to the death of M. alternatus due to energy shortage if they adhered to their original oviposition strategy. Whereas the novel oviposition strategy involved depositing multiple non-viable eggs within a single slit, which could reduce the number of oviposition times and conserve more energy to cope with heat stress. Overall, our findings suggested that this novel oviposition strategy might help alleviate the adverse effects of EHTs by saving more energy. Consequently, this strategy contributed to the long-term survival of the population in the context of climate warming.

Funding

This work was supported by the National Natural Science Foundation of China [Grant number 32201562] to Hui Li, Basic Research Program Natural Science Foundation of Jiangsu Province [Grant number BK20220412] to Hui Li, and the Excellent Postdoctoral Program of Jiangsu Province to Hui Li.

Competing Interests

The authors declare that they have no competing interests.

Author Contributions

Hui Li and Dejun Hao conceived and designed research. Hui Li and Jin Chen conducted experiments. Shouyin Li contributed new reagents and/or analytical tools. Hui Li, Jin Chen and Yushan Tan analyzed data. Hui Li wrote the manuscript. Jianren Ye and Shouyin Li revised the manuscript. All authors read and approved the manuscript.

Data availability

The datasets generated during this study are available at Figshare (doi:10.6084/m9.figshare.24182406). Further information and requests for resources should be directed to and will be fulfilled by the corresponding author, Dejun Hao ([email protected]).

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No competing interests reported.

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The pine sawyer beetle alters oviposition strategy in response to extreme high temperatures

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Abstract

Figures

Key message

Introduction

Material and methods

Insect rearing and collection

Extreme high temperature treatments

Reproductive performance

Counts of viable sperms in spermatheca

Data analysis

Results

EHTs impact on fecundity

EHTs impact on offspring performance

Oviposition strategy under EHTs

Relevance of egg hatchability, vitality sperms and novel oviposition strategy

Discussion

Stage-specific differences in detrimental effects of EHTs on reproduction

Sex-specific differences in detrimental effects of EHTs on reproduction

Response of oviposition strategy to EHTs

Declarations

References

Additional Declarations

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