LC50 of lambda-cyhalothrin stimulates reproduction on the moth Mythimna separata (Walker)

The interplay between temperature and an insecticide mixture modulates the stimulatory response of sublethally exposed Myzus persicae

Temperature can interact with chemical pesticides and modulate their toxicity. Sublethal exposure to pesticides is known to trigger hormetic responses in pests. However, the simultaneous effects of temperature and sublethal exposure to single or mixture-based insecticides on the insects' stimulatory responses are not frequently considered in toxicological studies. Here we investigated the combined effects of temperature on the lethal and sublethal responses of the green peach aphid Myzus persicae after exposure to commercial formulations of a neonicotinoid (thiamethoxam) and a pyrethroid (lambda-cyhalothrin) and their mixture. Firstly, the concentration-response curves of the insecticides were determined under four temperatures (15 °C, 20 °C, 25 °C, and 28 °C) by the leaf dipping method. Subsequently, the sublethal concentrations C0, CL1, CL5, CL10, CL15, CL20, and CL30 were selected to assess sublethal effects on aphids' longevity and reproduction under the same temperatures. The results showed that the mixture of thiamethoxam + lambda-cyhalothrin caused greater toxicity to aphids compared to the formulations with each active ingredient alone and that the toxicity was higher at elevated temperatures. Furthermore, the exposure to low concentrations of the mixture (thiamethoxam + lambda-cyhalothrin) and the separated insecticides induced stimulatory responses in the longevity and fecundity of exposed aphid females, but the occurrence of such hormetic responses depended on the insecticide type, its sublethal concentration, and the temperature as well as their interactions.

Four New Furofuran Lignans from Phryma leptostachya Inhibit the Accumulation of Molting Hormones in Armyworm

Furofuran lignans have been identified as the main substances responsible for the biological activities of the plant genus Phryma. Here, four new phrymarolin-type leptolignans A-D (7-10) and eight previously known lignans were isolated from P. leptostachya. Of these, nine exhibited significant antifeedant activity against armyworm (Mythimna separata) through a dual-choice bioassay, with the EC50 values ranging from 0.58 to 10.08 μg/cm2. In particular, the newly identified lignan leptolignan A (7) showed strong antifeedant activity, with an EC50 value of 0.58 ± 0.34 μg/cm2. Further investigation found that leptolignan A can inhibit the growth and nutritional indicators in the armyworm M. separata. The concentrations of two molting hormones, 20-hydroxyecdysone and ecdysone, were also found to decrease significantly following the treatment of the armyworms with the lignan, implying that the target of the P. leptostachya lignan may be involved in 20-hydroxyecdysone and ecdysone synthesis. These results enrich our knowledge of P. leptostachya metabolite structural diversity, and provide a theoretical basis for the control of armyworm using lignans.

Sublethal Effects of Emamectin Benzoate on Development and Reproduction and RNAi of the Vitellogenin Gene in Spodoptera frugiperda

Spodoptera frugiperda, one of the most destructive corn pests in the world, invaded China in December 2018. In this study, sublethal concentrations (LC10 and LC30) of emamectin benzoate (EB) were used to treat pesticide-free treatment (PFT) and EB treatment (ET) of S. frugiperda. In PFT, compared with the control (CK), the pupal weight, hatching rate, and pupation rate of LC10 and LC30 groups were significantly reduced. The fecundity and the expression of vitellogenin gene (SfVg) were decreased after LC30 treatment, while the LC10 treatment groups showed no significant difference from the control group. In ET, compared to CK, the fecundity was increased by 11.14 and 18.8%. The expression of SfVg was upregulated by 2.6 times after LC30 treatment. Moreover, RNAi-mediated SfVg knockdown resulted in a nearly 70% reduction in oviposition. The result provided a theoretical basis for optimizing the application of EB and Vg-dsRNA in the control of S. frugiperda.

The Lethal and Sublethal Effects of Lambda-Cyhalothrin and Emamectin Benzoate on the Soybean Pest Riptortus pedestris (Fabricius)

Riptortus pedestris (Fabricius, 1775) (Hemiptera: Alydidae) is a major soybean pest in East Asia that can cause soybean staygreen syndrome. To date, no insecticides have been registered for the control of R. pedestris in China, and these insects are primarily controlled in the field through the application of broad-spectrum insecticides including lambda-cyhalothrin (LCT) and emamectin benzoate (EMB). Here, the lethal and sublethal effects of LCT and EMB on R. pedestris were comprehensively evaluated. LCT and EMB were both found to exhibit high levels of toxicity and concentration-dependent repellent effects for R. pedestris. The exposure of third instar nymphs from the F0 generation to LC30 concentrations of LCT and EMB resulted in a significant increase in the duration of nymph development and adult pre-oviposition period (APOP), together with reductions in fifth instar nymph and adult body weight, longevity, oviposition days, fecundity, vitellarium length, lateral oviduct diameter, and vitellogenin (Vg) gene expression as compared to control treatment. Strikingly, these suppressive effects were transmitted to the F1 generation, which similarly experienced the prolongation of preadult development and the preoviposition period (TPOP). Relative to control-treated populations, the F1 generation for these insecticide-treated groups also exhibited significant decreases in population parameter values. Overall, these data offer new insight into the impact that LCT and EMB treatment can have on R. pedestris, providing a valuable foundation for the application of these pesticides in the context of integrated pest management strategies aimed at soybean crop preservation.

New insights into Microalgal astaxanthin's effect on Lambda-cyhalothrin-induced lymphocytes immunotoxicity in Cyprinus carpio: Involving miRNA-194-5p-FoxO1-mediated-mitophagy and pyroptosis

Lambda-cyhalothrin (LC), a pyrethroid insecticide widely used in agriculture, causes immunotoxicity to aquatic organisms in the aquatic environment. Microalgal astaxanthin (MA) is a natural carotenoid that enhances viability of a variety of fish. To investigate the immunotoxicity of LC and the improvement effect of MA in lymphocytes (Cyprinus carpio), lymphocytes were treated with LC (80 M) and/or MA (50 M) for 24 h. Firstly, CCK8 combined with PI staining results showed that MA significantly attenuated the LC-induced lymphocyte death rate. Secondly, LC exposure resulted in excessively damaged mitochondrial and mtROS, diminished mitochondrial membrane potential and ATP content, which could be improved by MA. Thirdly, MA upregulated the levels of mitophagy-related regulatory factors (Beclin1, LC3, ATG5, Tom20 and Lamp2) induced by LC. Importantly, MA decreased the levels of pyroptosis-related genes treated with LC, including NLRP3, Cas-4, GSDMD and active Cas-1. Further study indicated that LC treatment caused excessive miRNA-194-5p and reduced levels of FoxO1, PINK1 and Parkin, which was inhibited by MA treatment. Overall, we concluded that MA could enhance damaged mitochondrial elimination by promoting the miRNA-194-5p-FoxO1-PINK1/Parkin-mitophagy in lymphocytes, which reduced mtROS accumulation and alleviated pyroptosis. It offers insights into the importance of MA application in aquaculture as well as the defense of farmed fish against agrobiological hazards in fish under LC.

Micro-algal astaxanthin improves lambda-cyhalothrin-induced necroptosis and inflammatory responses via the ROS-mediated NF-κB signaling in lymphocytes of carp (Cyprinus carpio L.)

Lambda-cyhalothrin (LCY) is a widely used toxic pesticide that causes harmful effects on the immune organs of fish and aquatic species. Micro-algal astaxanthin (MAA), a heme pigment found in haematococcus pluvialis, has been shown to benefit antioxidants and immunity in aquaculture. To investigate how MAA protects carp lymphocytes from LCY-induced immunotoxicity, a model of fish lymphocytes treated with LCY and/or MAA was established. Lymphocytes from carp (Cyprinus carpio L.) were given LCY (80 μM) and/or MAA (50 μM) as a treatment for a period of 24 h. Firstly, LCY exposure resulted in excessive ROS and malondialdehyde production and reduces antioxidant enzymes (SOD and CAT), indicating a reduced capacity of the antioxidant system. Secondly, the results of flow cytometry and AO/EB labeling proved that lymphocytes treated with LCY have a larger ratio of necroptosis. In addition, LCY upregulated the levels of necroptosis-related regulatory factors (RIP1, RIP3 and MLKL) via the ROS-mediated NF-κB signaling pathway in lymphocytes. Thirdly, LCY treatment caused increased secretion of inflammatory genes (IL-6, INF-γ, IL-4, IL-1β and TNF-α), leading to immune dysfunction in lymphocytes. Surprisingly, LCY-induced immunotoxicity was inhibited by MAA treatment, indicating that it effectively attenuated the LCY-induced changes described above. Overall, we concluded that MAA treatment could ameliorate LCY-induced necroptosis and immune dysfunction by inhibiting the ROS-mediated NF-κB signaling in lymphocytes. It provides insights into the protection of farmed fish from agrobiological threats in fish under LCY and the value of MAA applications in aquaculture.

Expressions and functions of RR-1 cuticular protein genes in the integument of Mythimna separata

As the most outer layer between itself and the environment, integuments are necessary for insects with various important functions. Cuticular proteins (CPs) are the main components in integuments, while the functions of CP genes remain unknown in Mythimna separata (Walker), which is a devastating agricultural pest. In this study, 79 CP genes were identified from the transcriptomes of larval integuments, 57 of which were from the family containing conserved Rebers & Riddiford (R&R) consensus (CPR family). Amongst these CPRs, 44 genes belonged to the subfamily with RR-1 motif (RR-1 genes) and clustered into three clades, with the top 15 most abundant RR-1 genes identified based on fragments per kilobase per million mapped fragments (FPKM) values. RT-qPCR analysis showed that most of RR-1 genes such as MsCPR1-4 were highly expressed at larval stages and in their integuments. The expression levels of RR-1 genes were generally decreased at the beginning but increased at the late stage of molting process. RNAi was applied for six RR-1 genes, and MsCPR1-4 were knocked down significantly. Silence of MsCPR2 resulted in abnormal integument formed after molting, while knockdown of MsCPR3 and MsCPR4 led to failure of molting, respectively. No phenotype was obtained for the RNAi of MsCPR1. Therefore, the expression of RR-1 genes and their functions were analyzed in the development of integuments in M. separata, providing new insights of RR-1 genes and potential targets for the development of growth regulators and new insecticides for M. separata.

Exposure to lambda-cyhalothrin and abamectin drives sublethal and transgenerational effects on the development and reproduction of Cydia pomonella

The codling moth Cydia pomonella (Lepidoptera: Tortricidae) is a major invasive pest of pome fruits and walnuts worldwide. Lambda-cyhalothrin (LCT) and abamectin (AM) have been frequently used in C. pomonella control, but control of this pest is very difficult because shortly after hatching, larvae of this insect bore tunnels and hide inside host plant fruit. In this study, a simulated field spray bioassay method was developed against neonate larvae of C. pomonella and concentration-response bioassays were conducted to evaluate the susceptibility of the neonate larvae to LCT and AM. Exposure of neonate larvae to sublethal concentration (LC₃₀) of LCT or AM significantly reduced the survival rate of larvae (4th and 5th instars), lowered the mean weight of larvae and pupae, and decreased the daily maximal number of eggs laid and the total number of eggs laid (fecundity) per female. The sublethal effects, including reduced body mass, mean fecundity and net reproductive rate, extended mean generation time, and shortened oviposition period, were also found in transgenerational offspring. Furthermore, the transgenerational maternal effects were more obvious for AM than LCT, in comparison to the control. Additionally, the estimated population size was decreased by exposure to LC₃₀ of LCT and AM, and the observed reduction of fecundity and population size within and across generations was likely the result of the downregulation of the reproduction-related vitellogenin gene (CpVg) after exposure to LC₃₀ of LCT and AM. These results provide a better understanding of the overall effects of LCT and AM on C. pomonella and the transgenerational effects which should be taken into consideration when using insecticides in order to control C. pomonella.

Review of molecular and biochemical responses during stress induced stimulation and hormesis in insects

The biphasic hormetic response to stress, defined by low-dose stimulation and high-dose inhibition is frequently observed in insects. Various molecular and biochemical responses associated with hormesis in insects have been reported in many studies, but no synthesis of all these findings has been undertaken. We conducted a systematic literature review, analyzing papers demonstrating phenotypic stimulatory effect(s) following exposure to stress where molecular or biochemical response(s) were also examined. Responses observed included stimulation of reproduction, survival and longevity, growth and development, and tolerance to temperature, chemical, or starvation and desiccation, in response to stressors including pesticides, oxidative stress, temperature, crowding and starvation, and radiation. Phenotypic stimulation ranged from <25% increased above controls to >100%. Reproductive stimulation was frequently <25% increased above controls, while stimulated temperature tolerance was frequently >100% increased. Molecular and biochemical responses had obvious direct connections to phenotypic responses in many cases, although not in all instances. Increased expression of heat shock proteins occurred in association with stimulated temperature tolerance, and increased expression of detoxification genes with stimulated pesticide or chemical tolerance, but also stimulated reproduction. Changes in the expression or activity of antioxidants were frequently associated with stimulation of longevity and reproduction. Stress induced changes in vitellogenin and juvenile hormone and genes in the IIS/TOR signalling pathway - which are directly responsible for regulating growth, development, and reproduction - were also reported. Our analysis showed that coordination of expression of genes or proteins associated with protection from oxidative stress and DNA and protein damage is important in the hormetic responses of insects.

The Efficacy of Chlorantraniliprole as a Seed Treatment for Mythimna separata (Walker) (Lepidoptera: Noctuidae)

The oriental armyworm (OAW), Mythimna separata (Walker) (Lepidoptera: Noctuidae), is an important pest in China and causes serious economic losses in corn. The anthranilic diamide, chlorantraniliprole (CHL), has been widely used as a seed treatment to control corn pests; however, no information is available on the efficacy of this insecticide as a seed treatment for OAW. In this study, the efficacy of seed treatment with CHL alone and CHL combined with the neonicotinoid insecticide clothianidin (CHL + CLO) was evaluated for controlling OAW larvae in the laboratory and field conditions. Pot experiments demonstrated that seed treatment with CHL and CHL + CLO (both 240 g a.i. 100 kg−1 seeds) resulted in >79% mortality of OAW larvae and a damage rate <20% in corn at 14 days after seed emergence (DAE). Similar to results obtained in pots, the residual toxicity of CHL and CHL + CLO to OAW larvae in the field declined with DAE and larval development. The control efficacy of field plots treated with CHL and CHL + CLO was >70% within 14 DAE, which was significantly higher than CLO alone. These results suggest that CHL and CHL + CLO as seed treatments could effectively reduce OAW larval infestation in corn. This study validates the effectiveness of corn seed treatment for OAW as an alternative to conventional foliar applications.

Influence of seasonal migration on the development of the insecticide resistance of oriental armyworm (Mythimna separata) to λ-cyhalothrin

BACKGROUND

The seasonal long-distance migration of pests amongst different seasonal habitats may encounter different degrees of insecticide selection pressure, but knowledge of the evolution of resistance and the underlying mechanisms remains sparse. Here, we show that the development of resistance of the oriental armyworm Mythimna separata (Walker), a notorious agricultural pest that migrates between northern and northeast China seasonally across the Bohai Gulf, is influenced by seasonal migration.

RESULTS

There are two conspicuous migrations of M. separata, the northeastwards population in the second half of May and the returning population in the second half of August, between northern and northeast China per year, and the abundance values of migrants from April to October are significantly different. The resistance levels of seasonal migratory populations to λ-cyhalothrin vary in different months, and the resistance levels and estimated frequency of the resistance allele of the first northeastward population (second half of May, May.-2) in spring are significantly higher than those of the returning populations in autumn. Moreover, resistance decline was observed in migrating population Jul.-2, with the resistance levels in the F₁ progeny higher than those in their F₂ progeny. Synergism tests indicate that cytochrome P450 monooxygenases (P450s) play a major role in resistance. Enzymatic assays show that P450 activity is significantly correlated with resistance levels in migratory populations, indicating that increased P450 activity is the main mechanism of resistance. The expression levels and correlation analysis of the relative expression of P450s with resistance levels show that three (CYP9A144, CYP9G40, and CYP6B79) out of 23 genes from CYP6 and CYP9 subfamilies are potentially involved in resistance to λ-cyhalothrin.

CONCLUSION

Our results show that the resistance of M. separata to λ-cyhalothrin is unstable and likely to be metabolically driven by enhanced P450 activity mediated by the overexpression of multiple P450 genes. Notably, the development of resistance is probably affected by seasonal migration.

Transcriptional identification of differentially expressed genes during the prepupal-pupal transition in the oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae)

The oriental armyworm, Mythimna separata (Walker) is a serious pest of agriculture that does particular damage to Gramineae crops in Asia, Europe, and Oceania. Metamorphosis is a key developmental stage in insects, although the genes underlying the metamorphic transition in M. separata remain largely unknown. Here, we sequenced the transcriptomes of five stages; mature larvae (ML), wandering (W), and pupation (1, 5, and 10 days after pupation, designated P1, P5, and P10) to identify transition-associated genes. Four libraries were generated, with 22,884, 23,534, 26,643, and 33,238 differentially expressed genes (DEGs) for the ML-vs-W, W-vs-P1, P1-vs-P5, and P5-vs-P10, respectively. Gene ontology enrichment analysis of DEGs showed that genes regulating the biosynthesis of the membrane and integral components of the membrane, which includes the cuticular protein (CP), 20-hydroxyecdysone (20E), and juvenile hormone (JH) biosynthesis, were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs were enriched in the metabolic pathways. Of these DEGs, thirty CP, seventeen 20E, and seven JH genes were differentially expressed across the developmental stages. For transcriptome validation, ten CP, 20E, and JH-related genes were selected and verified by real-time PCR quantitative. Collectively, our results provided a basis for further studies of the molecular mechanism of metamorphosis in M. separata.

Biocidal efficacy of tutin and its influence on immune cells and expression of growth-blocking and neuroglian peptides in Mythimna separata (Lepidoptera: Noctuidae)

Mythimna separata Walker (Lepidoptera: Noctuidae) is one of the major pests that can cause severe damage to grain crops. The development of low-toxicity and high-performance botanical insecticides is becoming the focus of new pesticide research to control M. separata. Tutin, a sesquiterpene lactone compound obtained from Coriaria sinica Maxim, a native Chinese poisonous plant, has antifeedant, absorption, and stomach poisoning against a variety of pests. To understand the toxic effect of tutin on M. separata larvae, we set out to determine their antifeedant, mortality, paralysis, weight change, and to examine the spreading of M. separata hemocytes under different concentrations of tutin treatment. Tissue distribution of the immune-associated gene growth-blocking peptide (GBP) and neuroglian peptide (Nrg) was detected by reverse transcription polymerase chain reaction (PCR). Furthermore, real-time quantitative PCR was carried out to determine the expression profiles of GBP and Nrg after different concentrations of tutin stimulation. Our results revealed that tutin exhibited significant antifeedant and insecticidal activities, paralysis, weight loss to M. separata. Besides, tutin significantly influenced on the morphology of hemocytes and enhanced the expression of GBP and Nrg in M. separata.

Reduced fecundity and regulation of reproductive factors in flubendiamide-resistant strains of Plutella xylostella

Diamondback moth (DBM), Plutella xylostella, is an important pest of crucifers worldwide. The extensive use of flubendiamide has led to the development of resistance in field populations and reports of control failures. In this study, the lab-selected (R_f) and field-collected (R_b) flubendiamide-resistant strains of P. xylostella with LC₅₀ resistance ratios of 1890-fold and 1251-fold, respectively, were used, as well as a lab-reared flubendiamide-susceptible strain (S). The results showed that the fecundity of the R_f and R_b-resistant strains was significantly lower than that of S strain. The contents of vitellin and transcripts of P. xylostella vitellogenin (PxVg) and P. xylostella vitellogenin receptor (PxVgR) genes in the R_f and R_b strains were significantly higher than those of S strains at 0-48 h after adult eclosion. At 96 h after eclosion, the content of vitellin in the R_f and R_b strains did not differ significantly from those of S strains, whereas transcripts of the PxVg and PxVgR genes in the R_f and R_b strains were significantly lower than that of the S strain. The content of the juvenile hormone III (JH III), β-ecdysone (20E), and the gene expression level of P. xylostella methoprene tolerant (PxMet) in the R_f and R_b strains were significantly higher than that of the S strain. The activity of trehalase was significantly higher in the R_f and R_b strains than that of the S strain in the first to the third instar larvae, whereas in the fourth instar larvae, there was no significantly difference in the three strains. At different times after adult eclosion, the differences in trehalase activity were erratic between the strains. The transcripts of P. xylostella trehalase (PxTre) gene in the R_f and R_b strains were significantly higher than that of the S strain in most developmental stages. Here, we report differences in fecundity between flubendiamide-resistant and susceptible strains of P. xylostella and discuss gene expression of several reproductive factors, which provides a possible explanation for the mechanism of fecundity reduction concurrent with flubendiamide-resistance in P. xylostella.

A dose of experimental hormesis: When mild stress protects and improves animal performance

The adaptive response characterized by a biphasic curve is known as hormesis. In a hormesis framework, exposure to low doses leads to protective and beneficial responses while exposures to high doses are damaging and detrimental. Comparative physiologists have studied hormesis for over a century, but our understanding of hormesis is fragmented due to rifts in consensus and taxonomic-specific terminology. Hormesis has been and is currently known by multiple names; preconditioning, conditioning, pretreatment, cross tolerance, adaptive homeostasis, and rapid stress hardening (mostly low temperature: rapid cold hardening). These are the most common names used to describe adaptive stress responses in animals. These responses are mechanistically similar, while having stress-specific responses, but they all can fall under the umbrella of hormesis. Here we review how hormesis studies have revealed animal performance benefits in response to changes in oxygen, temperature, ionizing radiation, heavy metals, pesticides, dehydration, gravity, and crowding. And how almost universally, hormetic responses are characterized by increases in performance that include either increases in reproduction, longevity, or both. And while the field can benefit from additional mechanistic work, we know that many of these responses are rooted in increases of antioxidants and oxidative stress protective mechanisms; including heat shock proteins. There is a clear, yet not fully elucidated, overlap between hormesis and the preparation for oxidative stress theory; which predicts part of the responses associated with hormesis. We discuss this, and the need for additional work into animal hormetic effects particularly focusing on the cost of hormesis.