Behavioural adaptation of the rice leaf folder Cnaphalocrocis medinalis to short-term heat stress

The genome and sex-dependent responses to temperature in the common yellow butterfly, Eurema hecabe

BACKGROUND

Lepidoptera (butterflies and moths) is one of the most geographically widespread insect orders in the world, and its species play important and diverse ecological and applied roles. Climate change is one of the biggest challenges to biodiversity this century, and lepidopterans are vulnerable to climate change. Temperature-dependent gene expression differences are of relevance under the ongoing climate crisis. However, little is known about how climate affects gene expression in lepidopterans and the ecological consequences of this, particularly with respect to genes with biased expression in one of the sexes. The common yellow butterfly, Eurema hecabe (Family Pieridae), is one of the most geographically widespread lepidopterans that can be found in Asia, Africa, and Australia. Nevertheless, what temperature-dependent effects there may be and whether the effects differ between the sexes remain largely unexplored.

RESULTS

Here, we generated high-quality genomic resources for E. hecabe along with transcriptomes from eight developmental stages. Male and female butterflies were subjected to varying temperatures to assess sex-specific gene expression responses through mRNA and microRNA transcriptomics. We find that there are more temperature-dependent sex-biased genes in females than males, including genes that are involved in a range of biologically important functions, highlighting potential ecological impacts of increased temperatures. Further, by considering available butterfly data on sex-biased gene expression in a comparative genomic framework, we find that the pattern of sex-biased gene expression identified in E. hecabe is highly species-specific, rather than conserved across butterfly species, suggesting that sex-biased gene expression responses to climate change are complex in butterflies.

CONCLUSIONS

Our study lays the foundation for further understanding of differential responses to environmental stress in a widespread lepidopteran model and demonstrates the potential complexity of sex-specific responses of lepidopterans to climate change.

Cuticular protein genes involve heat acclimation of insect larvae under global warming

Cuticular proteins (CPs) play important roles in insect growth and development. However, it is unknown whether CPs are related to heat tolerance. Cnaphalocrocis medinalis, a serious pest of rice, occurs in summer and exhibits strong adaptability to high temperature, but the underlying mechanism is unclear. Here, the role of CP genes in heat acclimation was studied. Heat tolerance of the heat-acclimated larvae was significantly stronger than the unacclimated larvae. The cuticular protein content in the heat-acclimated larvae was higher than that of the unacclimated larvae. 191 presumed CP genes of C. medinalis (CmCPs) were identified. Expression patterns of 14 CmCPs were different between the heat acclimated (S39) and unacclimated (S27) larvae under heat stress. CmCPs were specifically expressed in epidermis and the head except CmCPR20 mainly expressed in Malpighian tubules. CmCPR20 was upregulated in S39 while downregulated in S27, but CmTweedle1 and CmCPG1 were upregulated in S27 and downregulated in S39. RNAi CmTweedle1 or CmCPG1 remarkably decreased heat tolerance and cuticular protein content of the heat-acclimated larvae but not the unacclimated larvae. RNAi CmCPR20 decreased heat tolerance and cuticular protein content of the unacclimated larvae but not the heat-acclimated larvae. CmTweedle1 and CmCPG1 genes involve heat acclimation of C. medinalis.

Characterization of heat exposure-associated escape behaviors and HSP gene expression in bed bugs (Cimex lectularius L.)

BACKGROUND

Heat can be effective for bed bug elimination. However, in some cases bed bugs survive heat treatments. The objectives of this study were to determine the behavioral responses of bed bugs to rising harborage temperatures (23.0-49.0 °C) and identify which heat shock protein (HSP) genes are expressed after heat exposure. First, a custom-made copper arena and harborage were used to determine the escape behaviors of six bed bug populations. Next, HSP gene expression responses of select populations were determined after heat exposure using real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Analysis of the 25 min behavioral experiment data found that harborage top temperatures associated with 25%, 50% and 75% probabilities of bed bugs to flee the harborage did not differ significantly between populations. Also, the percentage of insects that escaped from heated areas and survived (4.0-12.0%) was not different between populations. However, when specific temperatures at which successful escapes occurred were statistically compared, the Poultry House population was found to flee the harborage at statistically higher temperatures (43.6 ± 0.5 °C) than others (40.5 ± 0.6-42.0 ± 0.7 °C). The RT-qPCR experiments revealed that the HSP70.1, HSP70.3, and Putative Small HSP genes were significantly up-regulated 15 min, 2, and 4 h post-heat exposure and decreased back to baseline levels by 24 h.

CONCLUSIONS

This study shows that when harborage top temperatures approach 40.0-43.0 °C, bed bugs will disperse in search for cooler areas. This work implicates the HSP70.1, HSP70.3, and Putative Small HSP genes in heat induced stress recovery of bed bugs. © 2021 Society of Chemical Industry.

Detection and Classification of Rice Infestation with Rice Leaf Folder (Cnaphalocrocis medinalis) Using Hyperspectral Imaging Techniques

The detection of rice leaf folder (RLF) infestation usually depends on manual monitoring, and early infestations cannot be detected visually. To improve detection accuracy and reduce human error, we use push-broom hyperspectral sensors to scan rice images and use machine learning and deep neural learning methods to detect RLF-infested rice leaves. Different from traditional image processing methods, hyperspectral imaging data analysis is based on pixel-based classification and target recognition. Since the spectral information itself is a feature and can be considered a vector, deep learning neural networks do not need to use convolutional neural networks to extract features. To correctly detect the spectral image of rice leaves infested by RLF, we use the constrained energy minimization (CEM) method to suppress the background noise of the spectral image. A band selection method was utilized to reduce the computational energy consumption of using the full-band process, and six bands were selected as candidate bands. The following method is the band expansion process (BEP) method, which is utilized to expand the vector length to improve the problem of compressed spectral information for band selection. We use CEM and deep neural networks to detect defects in the spectral images of infected rice leaves and compare the performance of each in the full frequency band, frequency band selection, and frequency BEP. A total of 339 hyperspectral images were collected in this study; the results showed that six bands were sufficient for detecting early infestations of RLF, with a detection accuracy of 98% and a Dice similarity coefficient of 0.8, which provides advantages of commercialization of this field.

Comparative transcriptome analysis of the rice leaf folder (Cnaphalocrocis medinalis) to heat acclimation

Background

The rice leaf folder Cnaphalocrocis medinalis Güenée is a serious insect pest of rice in Asia. This pest occurs in summer, and it is sensitive to high temperature. However, the larvae exhibit heat acclimation/adaptation. To understand the underlying mechanisms, we established a heat-acclimated strain via multigenerational selection at 39 °C. After heat shock at 41 °C for 1 h, the transcriptomes of the heat-acclimated (S-39) and unacclimated (S-27) larvae were sequenced, using the unacclimated larvae without exposure to 41 °C as the control.

Results

Five generations of selection at 39 °C led larvae to acclimate to this heat stress. Exposure to 41 °C induced 1160 differentially expressed genes (DEGs) between the heat-acclimated and unacclimated larvae. Both the heat-acclimated and unacclimated larvae responded to heat stress via upregulating genes related to sensory organ development and structural constituent of eye lens, whereas the unacclimated larvae also upregulated genes related to structural constituent of cuticle. Compared to unacclimated larvae, heat-acclimated larvae downregulated oxidoreductase activity-related genes when encountering heat shock. Both the acclimated and unacclimated larvae adjusted the longevity regulating, protein processing in endoplasmic reticulum, antigen processing and presentation, MAPK and estrogen signaling pathway to responsed to heat stress. Additionally, the unacclimated larvae also adjusted the spliceosome pathway, whereas the heat-acclimated larvae adjusted the biosynthesis of unsaturated fatty acids pathway when encountering heat stress. Although the heat-acclimated and unacclimated larvae upregulated expression of heat shock protein genes under heat stress including HSP70, HSP27 and CRYAB, their biosynthesis, metabolism and detoxification-related genes expressed differentially.

Conclusions

The rice leaf folder larvae could acclimate to a high temperature via multigenerational heat selection. The heat-acclimated larvae induced more DEGs to response to heat shock than the unacclimated larvae. The changes in transcript level of genes were related to heat acclimation of larvae, especially these genes in sensory organ development, structural constituent of eye lens, and oxidoreductase activity. The DEGs between heat-acclimated and unacclimated larvae after heat shock were enriched in the biosynthesis and metabolism pathways. These results are helpful to understand the molecular mechanism underlying heat acclimation of insects.

Multigenerational heat acclimation increases thermal tolerance and expression levels of Hsp70 and Hsp90 in the rice leaf folder larvae

Physiological response and acclimation to thermal stress is a key strategy of insects to cope with changing climate. The underlying mechanism of heat acclimation in insects is still unclear. Here, the heat selection and transcript level response in the larvae of the rice leaf folder Cnaphalocrocis medinalis Güenée, a serious pest of rice in summer, were studied. The survival and fecundity of larvae during multigenerational heat selection at 39 °C were examined, and heat tolerance and mRNA expression of heat shock protein 70 (Hsp70) and 90 (Hsp90) were examined under heat stress. The results showed that survival and fecundity of larvae increased notably and then kept constant after two or three generations of heat selection. Heat selection improved thermal tolerance of larvae. The Hsp70 mRNA expression of the 3rd-instar larvae increased in all five generations of heat selection, but Hsp90 increased only in the first two generations. The response of Hsp70 to 39 °C heat treatment in the larvae kept at 27 °C was different from the larvae exposed to the conditioning heat treatments, but the response of Hsp 90 was similar. Moreover, the Hsp70 and Hsp90 mRNA expression levels were significantly higher in the heat-acclimated larvae than that in the unacclimated larvae at a comparable duration of exposure to 37 and 41 °C. Selection at a high temperature across multiple generations led larvae to heat acclimation, and Hsp70 and Hsp90 were involved in this acclimation process.

Rice Leaf Folder Larvae Alter Their Shelter-Building Behavior and Shelter Structure in Response to Heat Stress

Behavioral thermoregulation is a key strategy for insects to cope with heat stress. The rice leaf folder Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) larvae usually fold one leaf to construct a leaf shelter. The larvae are vulnerable to heat stress, and the temperature in summer is often beyond the optimal range of them. Shelters confer protection against environmental stress but unclear whether larvae will alter shelter-building behavior when encountering heat stress. We observed the shelter-building behavior of larvae during and after heat shock, and then examined the shape and structure of shelters. Larvae spent more time in selecting a site and building a shelter during and after heat shock than at the optimal temperature. More than 70% of larvae folded two or three leaves to build a shelter during and after heat shock, but more than 60% of larvae only folded one leaf at the optimal temperature. Larvae built more single-leaf longitudinal shelters at the optimal temperature, but they built more multileaf overlapping shelters during and after heat stress. Larvae constructed a short leaf shelter using a small amount of silk binds when they were exposed to 40°C for 4 h. The rice leaf folder larvae can alter their shelter-building behavior and shelter structure in response to heat stress.

Effect of Steam Treatment on Feeding, Mating, and Fecundity of the Common Bed Bug (Hemiptera: Cimicidae)

Steam application is an effective and environmentally friendly method for controlling bed bugs, Cimex lectularius L. (Hemiptera: Cimicidae). While a few studies documented the bed bug control efficacy of steam treatment, the sublethal effect of steam treatment on bed bug behavior and female fecundity is unknown. In this study, we evaluated the effect of steam treatment on the movement, feeding, mating behavior, and fecundity of female bed bugs in the laboratory. Bed bug adults received a calibrated steam treatment that caused approximately 28% mortality. The surviving bed bugs were observed for their feeding and mating behavior at 1 d posttreatment, female fecundity during a 7-d observation period, and offspring hatching. Steam-treated bed bugs were less active based on the percentage of bed bugs with movement, moving distance during a 10-min observation period, and feeding rate. However, steam treatment had no significant effect on blood intake (amount of blood taken per meal) among the fed bed bugs. After blood feeding, the steam-treated bed bugs had similar mating events and egg production as the control bed bugs. Furthermore, parental steam exposure had no significant effect on the offspring hatching. In conclusion, steam treatment could temporarily decrease bed bug activity levels and feeding rate, but had no significant impact on bed bug mating behavior and female fecundity.