Effects of high temperature on life history traits and heat shock protein expression in chlorpyrifos-resistant Laodelphax striatella

Constitutively expressed small heat shock protein LsHsp21.5 not only enhances heat tolerance but also helps to maintain reproduction in female Laodelphax striatellus

Coping with stressful conditions and maintaining reproduction are two key biological processes that affect insect population dynamics. Small heat shock proteins (sHSPs) are involved in the stress response and the development of insects. The sHsp gene Laodelphax striatellus (Hemiptera: Delphacidae) sHsp 21.5 (LsHsp21.5) showed constitutive, stage- and organ-specific expression in L. striatellus, a pest that damages cultivated rice in east Asia. The expression of LsHsp21.5 was highest in the ovary, with 43.60, 12.99 and 1.45 time higher expression here than in the head, gut and female fat bodies, respectively. The expression of this gene was weakly affected by heat or cold shock. The gene provided in vitro protection against heat damage to malate dehydrogenase and in vivo protection against heat stress in Escherichia coli (Enterobacteriales: Enterobacteriaceae) BL21(DE3) and L. striatellus. Moreover, L. striatellus reproduction decreased by 1.85 times when the expression of LsHsp21.5 was inhibited by RNA interference. The expression of some genes related to reproduction, such as the homologous gene of chorion protein, also declined. These results suggest that LsHsp21.5 expression not only protects other proteins against stress but also helps maintain the stable expression of some reproduction-related genes under non-stressful conditions, with impacts on L. striatellus fecundity.

Molecular and functional characterization of heat-shock protein 70 in Aphis gossypii under thermal and xenobiotic stresses

Aphis gossypii, a globally distributed and economically significant pest of several crops, is known to infest a wide range of host plants. Heat shock proteins (Hsps), acting as molecular chaperones, are essential for the insect's environmental stress responses. The present study investigated the molecular characteristics and expression patterns of AgHsp70, a heat shock protein gene, in Aphis gossypii. Our phylogenetic analysis revealed that AgHsp70 shared high similarity with homologs from other insects, suggesting a conserved function across species. The developmental expression profiles of AgHsp70 in A. gossypii showed that the highest transcript levels were observed in the fourth instar nymphs, while the lowest levels were detected in the third instar nymphs. Heat stress and exposure to four different xenobiotics (2-tridecanone, tannic acid, gossypol, and flupyradifurone (4-[(2,2-difluoroethyl)amino]-2(5H)-furanone)) significantly up-regulated AgHsp70 expression. Knockdown of AgHsp70 using RNAi obviously increased the susceptibility of cotton aphids to 2-tridecanone, gossypol and flupyradifurone. Dual-luciferase reporter assays revealed that gossypol and flupyradifurone significantly enhanced the promoter activity of AgHsp70 at a concentration of 10 mg/L. Furthermore, we identified the transcription factor heat shock factor (HSF) as a regulator of AgHsp70, as silencing AgHSF reduced AgHsp70 expression. Our results shed light on the role of AgHsp70 in xenobiotic adaptation and thermo-tolerance.

Identification of a fatty acid synthase gene (FAS1) from Laodelphax striatellus planthoppers contributing to fecundity

Fatty acid synthase (FAS) is a multifunctional enzyme that plays an important role in the formation of fatty acids. The fatty acids take part in many processes, such as cell signaling and energy metabolism, and in insects they are important in both cuticular hydrocarbon (CHC) formation and reproduction. Here we characterized the sequence structure and function of an FAS from the small brown planthopper (SBPH), Laodelphax striatellus. The full-length open reading frame (ORF) sequence of LsFAS1 was 7122 bp, encoding a predicted protein of 2373 amino acid residues. There were 7 functional domains in the LsFAS1 protein sequence. Gene expression screening by real-time quantitative polymerase chain reaction (RT-qPCR) showed that LsFAS1 was expressed in all developmental stages. Relative expression was highest at the 4th-instar and female adult stages. Among different tissues, the expression level of LsFAS1 in the ovary was the highest. Phylogenetic analysis showed that LsFAS1 clustered in a clade with 2 FASs from Nilaparvata lugens. Furthermore, these 3 FASs are related to cockroach BgFAS and locust LmFAS. After RNA interference-mediated knock-down, most treated insects died at eclosion. In addition, the lifespan of dsFAS1-treated female adults was shorter than that of the dsGFP-injected control, and offspring production decreased. Also, the expression of vitellogenin (Vg) and vitellogenin receptor (VgR) genes decreased. Virgin females dissected at days 2 and 4 post-eclosion showed many matured oocytes in planthoppers treated with dsGFP but not with dsFAS1. These data highlight the importance of LsFAS1 in SBPH, including a role in reproduction.

Fitness studies of insecticide resistant strains: lessons learned and future directions

The evolution of insecticide resistance is generally thought to be associated with a fitness cost in the absence of insecticide exposure. However, it is not clear how these fitness costs manifest or how universal this phenomenon is. To investigate this, we conducted a literature review of publications that studied fitness costs of insecticide resistance, selected papers that met our criteria for scientific rigor, and analyzed each class of insecticides separately as well as in aggregate. The more than 170 publications on fitness costs of insecticide resistance show that in 60% of the experiments there is a cost to having resistance, particularly for measurements of reversion of resistance and reproduction. There were differences between classes of insecticides, with fitness costs seen less commonly for organochlorines. There was considerable variation in the experiments performed. We suggest that future papers will have maximum value to the community if they quantitatively determine resistance levels, identify the resistance mechanisms present (and the associated mutations), have replicated experiments, use related strains (optimally congenic with the resistance mutation introgressed into different genetic backgrounds) and measure fitness by multiple metrics. Studies on the fitness costs of insecticide resistance will continue to enlighten our understanding of the evolutionary process and provide valuable information for resistance management. © 2021 Society of Chemical Industry.

Fitness Cost of Chlorpyrifos Resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) on Different Host Plants

Spodoptera frugiperda (J. E. Smith, 1797) is a polyphagous pest of global relevance due to the damage it inflicts on agricultural crops. In South American countries, this species is one of the principal pests of maize and cotton. Currently, S. frugiperda is also emerging as an important pest of soybeans and winter cereals in Brazil. Chemical control is one of the main control tactics against S. frugiperda, even though resistance against numerous modes of action insecticides has been reported. To support insect resistance management programs, we evaluated the fitness costs of resistance of S. frugiperda to the acetylcholinesterase inhibitor chlorpyrifos. Fitness costs were quantified by comparing biological parameters of chlorpyrifos-resistant and -susceptible S. frugiperda and their F1 hybrids (heterozygotes) on non-Bt cotton, non-Bt maize, non-Bt soybean, and oats. The results revealed that the chlorpyrifos-resistant genotype showed lower pupa-to-adult and egg-to-adult survivorship and reduced larval weights on oats; longer neonate-to-pupa and egg-to-adult developmental periods, and lower pupal weights and fecundity on maize; lower pupal weights on soybean; and reduced fecundity on cotton compared with the chlorpyrifos-susceptible genotype. Fitness costs also affected fertility life table parameters of the resistant genotype, increasing the mean length of a generation on cotton and maize and reducing the potential for population growth on all hosts. These findings suggest fitness costs at the individual and population levels of chlorpyrifos resistance in S. frugiperda, indicating that removal of the selective agent from the environment would result in reduced resistance and opportunities for the restoration of susceptibility.

Effects of abiotic stress on the expression of Hsp70 genes in Sogatella furcifera (Horváth)

Sogatella furcifera (Horváth), a prominent rice pest in Asia, is a typical R-strategic and highly adaptable insect. Heat shock proteins (Hsps) are highly conserved molecular chaperones regulating responses to various abiotic stresses; however, limited information is available regarding their role in responding to abiotic stress in S. furcifera. This study aimed to investigate the effect of abiotic stresses on the expression of Hsp70 genes in the S. furcifera. Five Hsp70 genes were isolated from S. furcifera, and the expression patterns at different developmental stages and temperatures, upon treatment with different insecticides and ultraviolet A (UV-A) stress, were analyzed. Hsp70 genes were expressed at different developmental stages. Hsp70-2, Hsp70-5, and Hsp70-6 were significantly upregulated upon heat shock at 40 °C for 30 min. Hsp70-3 and Hsp70-4 were significantly upregulated upon heat shock at 30 °C for 30 min. Under UV-A stress, Hsp70-3, Hsp70-4, Hsp70-5, and Hsp70-6 were significantly upregulated. Conversely, Hsp70-2 was significantly downregulated under UV-A stress. The five Hsp70 genes were significantly downregulated in 3rd-instar nymphs on exposure to thiamethoxam, buprofezin, and avermectin at LC10 and LC25 concentrations. Hence, Hsp70 genes significantly contribute to the tolerance of S. furcifera to temperature and UV-A stress; however, they are not involved in the response to insecticides.

HSP superfamily of genes in the malaria vector Anopheles sinensis: diversity, phylogenetics and association with pyrethroid resistance

BACKGROUND

Heat shock proteins (HSPs) are molecular chaperones that are involved in many normal cellular processes and various kinds of environmental stress. There is still no report regarding the diversity and phylogenetics research of HSP superfamily of genes at whole genome level in insects, and the HSP gene association with pyrethroid resistance is also not well known. The present study investigated the diversity, classification, scaffold location, characteristics, and phylogenetics of the superfamily of genes in Anopheles sinensis genome, and the HSP genes associated with pyrethroid resistance.

METHODS

The present study identified the HSP genes in the An. sinensis genome, analysed their characteristics, and deduced phylogenetic relationships of all HSPs in An. sinensis, Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti by bioinformatic methods. Importantly, the present study screened the HSPs associated with pyrethroid resistance using three field pyrethroid-resistant populations with RNA-seq and RT-qPCR, and looked over the HSP gene expression pattern for the first time in An. sinensis on the time-scale post insecticide treatment with RT-qPCR.

RESULTS

There are 72 HSP genes in An. sinensis genome, and they are classified into five families and 11 subfamilies based on their molecular weight, homology and phylogenetics. Both RNA-seq and qPCR analysis revealed that the expression of AsHSP90AB, AsHSP70-2 and AsHSP21.7 are significantly upregulated in at least one field pyrethroid-resistant population. Eleven genes are significantly upregulated in different period after pyrethroid exposure. The HSP90, sHSP and HSP70 families are proposed to be involved in pyrethroid stress response based in expression analyses of three field pyrethroid-resistant populations, and expression pattern on the time scale post insecticide treatment. The AsHSP90AB gene is proposed to be the essential HSP gene for pyrethroid stress response in An. sinensis.

CONCLUSIONS

This study provides the information frame for HSP superfamily of genes, and lays an important basis for the better understanding and further research of HSP function in insect adaptability to diverse environments.

Induced expression of small heat shock proteins is associated with thermotolerance in female Laodelphax striatellus planthoppers

Insects are often exposed to high temperature stress in natural environments, but the mechanisms involved in thermotolerance in many insect groups like Hemiptera are not well known. To explore possible mechanisms of thermotolerance in the hemipteran pest Laodelphax striatellus, which damages rice through direct feeding and viral transmission, small heat shock proteins (sHsps) implicated in thermotolerance in other insect groups were identified. The seven sHsps identified have a conserved alpha crystallin domain, a variable N-terminal region, and shared relative low identities to each other. Three of the sHsp genes (LsHsp20.5, LsHsp21.5, and LsHsp21.6) exhibited higher basal expression than the other four genes but showed weak or no heat-induced expression. The other four genes (LsHsp20.1, LsHsp21.2, LsHsp21.4, and LsHsp22.0) were induced up to 3306-fold by heat. Injection of dsRNA indicated that expression of these sHsps was associated with thermotolerance, and Escherichia coli transformed with LsHsp21.2 and LsHsp20.1 showed relatively higher thermotolerance. These results point to an important functional role of these sHsps for thermotolerance in L. striatellus.

Temperature effects on life history traits of two sympatric branchiopods from an ephemeral wetland

Temperature effects on organisms are of multiple scientific interests, such as for their life history performance and for the study of evolutionary strategies. We have cultured two sympatric branchiopod species from an ephemeral pond in northern Taiwan, Branchinella kugenumaensis and Eulimnadia braueriana, and compared their hatching rate, maturation time, sex ratio, growth of body length, survivorship, clutch size, net reproductive rate R₀, generation time T_G, and intrinsic rate of natural increase r in relation to temperature (15, 20, 25 and 30°C). We found that E. braueriana had a significantly higher temperature-dependent fecundity and intrinsic population growth pattern (R₀ and r). In contrast, B. kugenumaensis reproduced much slower than E. braueriana with much lower R₀ (90–100 folds less) and r (about 10 folds less) at 15, 20 and 25°C and with a double as long T_G at 20 and 25°C. In addition, E. braueriana increased its chance of hermaphroditic sexual reproductive mode at higher temperature because of a significantly delayed maturation of males from hermaphrodites. In contrast, B. kugenumaensis showed no significant change in reproductive mode with temperature. This is the first study indicating a significant differentiation in life history parameters of two sympatric branchiopods mediated by temperature.