Mechanisms Of Insect Resistance Research Articles

Molecular Characterization Analysis and Adaptive Responses of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Nutritional and Enzymatic Variabilities in Various Maize Cultivars.

The fall armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), a common agricultural pest known for its extensive migration and wide host ranges, causes considerable harm to maize (Zea mays L.). In this study, we utilized two molecular marker genes, COI and Tpi, to compare the genetic characteristics of the collected original samples. Additionally, through an interactive study between S. frugiperda larvae and six maize varieties aiming to understand the insect's adaptability and resistance mechanisms, our analysis revealed that both the COI and Tpi genes identified S. frugiperda as the corn strain. Further examination of the larvae showed significant differences in nutritional indices, digestive, and detoxification enzyme activities. Special maize varieties were found to offer higher efficiency in nutrient conversion and assimilation compared with common varieties. This study revealed adaptations in S. frugiperda's digestive and detoxification processes in response to the different maize varieties. For instance, larvae reared on common maize exhibited elevated amylase and lipase activities. Interestingly, detoxification enzyme activities exhibited different patterns of variation in different maize varieties. The Pearson correlation analysis between nutritional indices, enzyme activities, and the nutritional content and secondary metabolites of maize leaves provided deeper insights into the pest's adaptability. The results highlighted significant relationships between specific nutritional components in maize and the physiological responses of S. frugiperda. Overall, our findings contribute substantially to the understanding of S. frugiperda's host plant adaptability, offering critical insights for the development of sustainable pest management strategies.

Characterization of Six Diamide Insecticides on Ryanodine Receptor: Resistance and Species Selectivity.

Ryanodine receptor (RyR) has been used as an insecticide target to control many destructive agricultural pests. The effectiveness of these insecticides has been limited by the spread of resistance mutations identified in pest RyRs, but the detailed molecular impacts of the individual mutations on the activity of different diamide compounds have not been fully explored. We created five HEK293 cell lines stably expressing wild type rabbit RyR1, wild type Spodoptera frugiperda RyR (Sf RyR), or Sf RyR carrying different resistance mutations, including G4891E, G4891E/I4734M, and Y4867F, respectively. R-CEPIA1er, a genetically encoded fluorescent protein, was also introduced in these cell lines to report the Ca2+ concentration in the endoplasmic reticulum. We systematically characterized the activities of six commercial diamide insecticides against different RyRs using the time-lapse fluorescence assay. Among them, cyantraniliprole (CYAN) displayed the highest activity against all three resistant Sf RyRs. The good performance of CYAN was confirmed by the toxicity assay using gene-edited Drosophila expressing the mutant RyRs, in which CYAN showed the lowest LD50 value for the double resistant mutant. In addition, we compared their acitivty between mammalian and insect RyRs and found that flubendiamide has the best insect-selectivity. The mechanism of the anti-resistance property and selectivity of the compounds was proposed based on the structural models generated by homology modeling and molecular docking. Our findings provide insights into the mechanism of insect resistance and guidance for developing effective RyR agonists that can selectively target resistant pests.

Effects of the Larch–Ashtree Mixed Forest on Contents of Secondary Metabolites in Larix olgensis

To understand the insect resistance mechanism of the larch, Larix olgensis, in a mixed forest, larch (Larix olgensis) seedlings and ashtree (Fraxinus mandshurica) seedlings were planted with mixed banding forests in the proportion of 1:1 (BMF1:1), 3:3 (BMF3:3) and 5:5 (BMF5:5), in pots and in the field. One year later, the content of secondary metabolites in the needles of each larch treatment were tested with an ultraviolet spectrophotometer. The results showed that the allelopathic effect of F. mandshuricas (ashtree) on L. olgensis (larch) could increase the content of secondary metabolites in larch needles. It was found that the flavonoid content in the needles of BMF5:5 was higher than that in the needles of BMF1:1 and BMF3:3 (p < 0.05). The tannin content in the needles of FBMF3:3 and FBMF5:5 was significantly higher than that of FBMF1:1, whereas the tannin content in the needles of PBMF3:3 reached 1.27 mg/g, which was the highest (p < 0.05). The lignin content in the needles of FBMF3:3 reached 2.27 mg/g, which was significantly more increased than that in the control group in a dose-dependent manner, while that in the needles of PBMF3:3 and PBMF5:5 was higher than that in the needles of PBMF1:1 (p < 0.05). The tannin and lignin content in the needles of FBMF was higher than that of PBMF. However, there was no difference in the content of flavonoids in the needles of FBMF and PBMF. These results suggest that banding mixed larches and ashtrees can significantly increase the content of secondary metabolites (phenolic compounds) in the needles of L. olgensis and improve its chemical defense, and the allelopathic effect of ashtrees on larches is related to the mixed proportion. Thus, the effect of mixed banding forests in the proportion of 3:3 and 5:5 is better.

Genome-Wide Identification of Brassica napus PEN1-LIKE Genes and Their Expression Profiling in Insect-Susceptible and Resistant Cultivars.

Recently, it has been reported that a gene (PEN1) in Arabidopsis thaliana is highly resistant to Plutella xylostella. We screened all the homologous genes of PEN1 in Arabidopsis thaliana and found that the motif of these genes was very conserved. At present, few insect resistance genes have been identified and characterized in Brassica napus. Therefore, we screened all the homologous genes containing this motif in the Brassica napus genome and systematically analyzed the basic information, conserved domain, evolutionary relationship, chromosomal localization and expression analysis of these genes. In this study, 12 PEN1 homologous genes were identified in the Brassica napus genome, which is more than the number in Arabidopsis thaliana. These genes are unevenly distributed on the 12 chromosomes in Brassica napus. Furthermore, all the PEN1 homologous genes contained light responsiveness elements, and most of the genes contained gibberellin-responsive elements, meJA-responsive elements and abscisic-acid-responsive elements. The results will provide a theoretical basis for screening insect resistance genes from the genome of Brassica napus and analyzing the molecular mechanism of insect resistance in Brassica napus.

Resistance to insecticides of housefly Musca domestica in the center of the European part of Russia

Under laboratory conditions, resistance to insecticides from various chemical classes of several strains of the housefly, Musca domestica, obtained from populations collected at facilities in the Moscow and Kaluga regions (KSK-1 in a cowshed and KSK-2 in the stable of an equestrian sports club, Krasnogorsk – at a food facility, Kaluga – in the compost of a garden non-profit partnership). It was found that when insecticides were applied topically, houseflies of all the studied strains hadthe highest resistance to cypermethrin (RF=75–900x) and to neonicotinoid compounds thiamethoxam and clothianidin (RF=95–330x). High resistance to fipronil was found in two strains of fly (RF= 46–75x). Strain KSK-1 was weakly tolerant to chlorpyrifos (RF=3.7x), while the other strains were susceptible. All the studied house fly strains were more susceptible to indoxacarb and chlorfenapyr than the laboratory strain S-NIID. The data indicate that studied housefly strains are multiresistant to almost all commonly used insecticides. Possible mechanisms of insect resistance to insecticides are discussed. Frequent use of insecticides of various chemical classes led to resistance in the target pest. Widespread use of pyrethroids in animal facilities has led to high resistance to them in the house fly because places where larvae hatch are constantly polluted with these insecticides. High resistance to neonicotinoids is also due to their frequent use as poisoned baits in livestock facilities. To the contrary, the studied housefly strains remained susceptible to the tested oxadiazines and pyrroles, chemical classes that were recently introduced to Russia.

Resistance of Cabbage Loopers to Bacillus thuringiensis (Bt) Toxin Cry1F and to Dual-Bt Toxin WideStrike Cotton Plants.

The Cry proteins from Bacillus thuringiensis (Bt) are major insecticidal toxins in formulated Bt sprays and are expressed in genetically engineered Bt crops for insect pest control. However, the widespread application of Bt toxins in the field imposes strong selection pressure on target insects, leading to the evolution of insect resistance to the Bt toxins. Identification and understanding of mechanisms of insect resistance to Bt toxins are an important approach for dissecting the modes of action of Bt toxins and providing knowledge necessary for the development of resistance management technologies. In this study, cabbage looper (Trichoplusia ni) strains resistant to the transgenic dual-Bt toxin WideStrike cotton plants, which express Bt toxins Cry1Ac and Cry1F, were selected from T. ni strains resistant to the Bt formulation Bt-DiPel. The WideStrike-resistant T. ni larvae were confirmed to be resistant to both Bt toxins Cry1Ac and Cry1F. From the WideStrike-resistant T. ni, the Cry1F resistance trait was further isolated to establish a T. ni strain resistant to Cry1F only. The levels of Cry1F resistance in the WideStrike-resistant and the Cry1F-resistant strains were determined, and the inheritance of the Cry1F-resistant trait in the two strains was characterized. Genetic association analysis of the Cry1F resistance trait indicated that the Cry1F resistance in T. ni isolated in this study is not shared with the Cry1Ac resistance mechanism nor is it associated with a mutation in the ABCC2 gene, as has so far been reported in Cry1F-resistant insects. IMPORTANCE Insecticidal toxins from Bacillus thuringiensis (Bt) are highly effective for insect control in agriculture. However, the widespread application of Bt toxins exerts strong selection for Bt resistance in insect populations. The continuing success of Bt biotechnology for pest control requires the identification of resistance and understanding of the mechanisms of resistance to Bt toxins. Cry1F is an important Bt toxin used in transgenic cotton, maize, and soybean varieties adopted widely for insect control. To understand the mode of action of Cry1F and mechanisms of Cry1F resistance in insects, it is important to identify Cry1F-specific resistance and the resistance mechanisms. In this study, Trichoplusia ni strains resistant to commercial "WideStrike" cotton plants that express Bt toxins Cry1Ac and Cry1F were selected, and a Cry1F-specific resistant strain was isolated. The isolation of the novel Cry1F-specific resistance in the T. ni provided an invaluable biological system to discover a Cry1F-specific novel resistance mechanism.

Advances in receptor-mediated resistance mechanisms of Lepidopteran insects to Bacillus thuringiensis toxin

Bacillus thuringiensis is widely used as an insecticide which is safe and environmentally friendly to humans and animals. One of the important insecticidal mechanisms is the binding of Bt toxins to specific toxin receptors in insect midgut and forming a toxin perforation which eventually leads to insect death. The resistance of target pests to Bt toxins is an important factor hampering the long-term effective cultivation of Bt crops and the continuous use of Bt toxins. This review summarizes the mechanism of insect resistance to Bt toxins from the perspective of important Bt toxin receptors in midgut cells of Lepidopteran insects, which may facilitate the in-depth study of Bt resistance mechanism and pest control.

Transcriptome profiling and RNA interference reveals relevant detoxification genes in Monochamus alternatus response to (+)‐α‐pinene

AbstractUnderstanding the mechanism of insect resistance to toxic effects of phytochemicals can provide an insight into plant–herbivore interactions. Monochamus alternatus Hope, a main vector of pine wood nematode (Bursaphelenchus xylophilus), prefers to infest masson pine (Pinus massoniana Lamb) and causes huge economic and environmental losses. α‐Pinene is the primary component of resin produced by masson pine and plays a crucial role in defending against herbivorous insects, but its defensive effects on M. alternatus larvae are barely known. Here, we explored the physiological metabolism in M. alternatus larvae that were fumigated with (+)‐α‐pinene, (‐)‐α‐pinene, β‐pinene, (R)‐(+)‐limonene, myrcene and (‐)‐α‐phellandrene. (+)‐α‐Pinene showed the highest fumigant toxicity to M. alternatus larvae among these monoterpenes, and the fourth instar larvae possessed the highest resistance to this compound at the larval stage. Comparative transcriptome analysis detected 423 up‐regulated and 311 down‐regulated genes in the larvae fumigated with (+)‐α‐pinene, which were mainly related to detoxification, energy and protein metabolism. Among the differentially expressed genes encoding for detoxification enzymes, 14 P450s, 13 UGTs, 1GSTs and 3ABCs were dramatically up‐regulated in the larvae fumigated with (+)‐α‐pinene. Silencing of P450s via RNA interference led to an increased mortality in the larval fumigated with (+)‐α‐pinene. Piperonyl butoxide exposure significantly increased the mortality and inhibited the expressions of P450s, UGTs and ABCs in the larvae fumigated with (+)‐α‐pinene. These results suggested an important role of P450s in the resistance of M. alternatus larvae to (+)‐α‐pinene fumigation, which may facilitate the understanding of terpenoid detoxification in M. alternatus larvae.

Comparative Transcriptome Analysis of Bt Resistant and Susceptible Strains in Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae)

The evolution of target pest population resistance to Bt toxins is the most relevant threat to the sustainability of Bt technology, thus it is necessary to clarify insect resistance mechanisms. Firstly, the resistance level of Asian corn borer was determined by bioassay. After 28 generations selection in the lab, the Cry1Ie-resistant strain (ACB-IeR) developed more than 862-fold resistance to Cry1Ie, and the Cry1F-resistant strain (ACB-FR) developed 961-fold resistance to Cry1F. The results show that long-term exposure to Bt toxins can lead to resistance. Then, we compared the differential expression genes (DEGs) of ACB-FR and ACB-IeR with susceptible strain (ACB-BtS), and analyzed GO function and KEGG pathway through transcriptome sequencing. The comparison showed that in Bt-resistant strains, many genes have a significant down-regulated trend. Several Bt-resistance candidate genes were differentially expressed in both resistant strains. Furthermore, the DEGs were verified by RT-qPCR and showed similar trend. These results provide candidate genes for further research on the Bt resistance mechanism.

MAP4K4 controlled transcription factor POUM1 regulates PxABCG1 expression influencing Cry1Ac resistance in Plutella xylostella (L.)

Deciphering the molecular mechanisms of insect resistance to Bacillus thuringiensis (Bt) based biotechnology products including Bt sprays and Bt crops is critical for the long-term application of Bt technology. Previously, we established that down-regulation of the ABC transporter gene PxABCG1, trans-regulated by the MAPK signaling pathway, contributed to high-level resistance to Bt Cry1Ac toxin in diamondback moth, Plutella xylostella (L.). However, the underlying transcriptional regulatory mechanism was unknown. Herein, we identified putative binding sites (PBSs) of the transcription factor (TF) POUM1 in the PxABCG1 promoter and used a dual-luciferase reporter assay (DLRA) and yeast one-hybrid (Y1H) assay to reveal that POUM1 activates PxABCG1 via interaction with one of these sites. The expression of POUM1 was significantly decreased in the midgut tissue of Cry1Ac-resistant P. xylostella strains compared to a Cry1Ac-susceptible P. xylostella strain. Silencing of POUM1 expression resulted in reduced expression of the PxABCG1 gene and an increase in larval tolerance to Bt Cry1Ac toxin in the Cry1Ac-susceptible P. xylostella strain. Furthermore, silencing of PxMAP4K4 expression increased the expression of both POUM1 and PxABCG1 genes in the Cry1Ac-resistant P. xylostella strain. These results indicate that the POUM1 induces PxABCG1 expression, while the activated MAPK cascade represses PxABCG1 expression thus reducing Cry1Ac susceptibility in P. xylostella. This result deepens our understanding of the transcriptional regulatory mechanism of midgut Cry receptor genes and the molecular basis of the evolution of Bt resistance in insects.

Characterizing serotonin biosynthesis in Setaria viridis leaves and its effect on aphids

A combined transcriptomic and metabolic analysis of Setaria viridis leaves responding to aphid infestation was used to identify genes related to serotonin biosynthesis. Setaria viridis (green foxtail), a short life-cycle C4 plant in the Poaceae family, is the wild ancestor of Setaria italica (foxtail millet), a resilient crop that provides good yields in dry and marginal land. Although S. viridis has been studied extensively in the last decade, the molecular mechanisms of insect resistance in this species remain under-investigated. To address this issue, we performed a metabolic analysis of S. viridis and discovered that these plants accumulate the tryptophan-derived compounds tryptamine and serotonin. To elucidate the defensive functions of serotonin, Rhophalosiphum padi (bird cherry-oat aphids) were exposed to this compound, either by exogenous application to the plant medium or with artificial diet bioassays. In both cases, exposure to serotonin increased aphid mortality. To identify genes that are involved in serotonin biosynthesis, we conducted a transcriptome analysis and identified several predicted S. viridis tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H) genes. Two candidate genes were ectopically expressed in Nicotiana tabacum, where SvTDC1 (Sevir.6G066200) had tryptophan decarboxylase activity, and SvT5H1 (Sevir.8G219600) had tryptamine hydroxylase activity. Moreover, the function of the SvTDC1 gene was validated using virus-induced gene silencing in S. italica, which caused a reduction in serotonin levels. This study provides the first evidence of serotonin biosynthesis in Setaria leaves. The biosynthesis of serotonin may play an important role in defense responses and could prove to be useful for developing more pest-tolerant Setaria italica cultivars.

Modern groups of insecticides: diamides and meta-diamides

The review summarizes and analyzes the data of foreign authors on the practical efficacy, mechanisms of action and insect resistance concerning insecticides of the groups of diamides and meta-diamides. The prospects of their application in Russia in agriculture and medical disinsection are considered. Insects resistant to OР’s, carbamates, pyrethroids remain the susceptibility to diamides and meta-diamides. Broflanilide, a pro-insecticide, which, due to its transformation into desmethylbroflanilide in the body of arthropods, acquires physicochemical properties leading to improved lipophilicity, water solubility, stability, affecting systemic activity, slowing down the action on harmful insects and increased selectivity for non-target species, is considered in detail. In several countries of the world where diamides are widely used in the controlling agricultural pests, a high resistance of several species of noctuids, diamondback moth, pyralid moths, tomato leafminer, etc. has been established. The key factors that determined the resistance to diamide in Thailand were the lack of insecticide rotation, minimal crop rotation, insufficient insecticide dosage, and irrigation. The necessity of introducing diamides and meta-diamides into the insecticide rotation schemes in order to control the insects resistant to traditionally used active substances was revealed.

Sanitary and epidemiological significance and resistance to insecticides of houseflies Musca domestica (Analytical Literature Review, 2000-2021)

Insect resistance to insecticides has been and remains a serious problem affecting insect control worldwide. The fight against houseflies is an important part of pest control measures due to the ability of insects to carry pathogens of infectious diseases of humans and animals. But many of the chemicals that have been shown to be effective against them cease to work after just a few years of use. The intensive use of insecticides in world practice has led to the development of natural populations of houseflies that are resistant to all groups of insecticides used to control them. This species is one of the ten insect species that have developed resistance to the maximal amount of active substances. The review summarizes and analyzes the data of foreign and Russian authors on the insecticide resistance of houseflies (Musca domestica L.) over the past 20 years. Data on the resistance of house flies to both traditional insecticides and new chemicals are presented. The main mechanisms of insect resistance and the factors of its development are described. Schemes of rotation of insecticides in the controlling winged flies are given. The review analyzed 101 sources from 11 countries of the world.

A cis-Acting Mutation in the PxABCG1 Promoter Is Associated with Cry1Ac Resistance in Plutella xylostella (L.).

The molecular mechanisms of insect resistance to Cry toxins generated from the bacterium Bacillus thuringiensis (Bt) urgently need to be elucidated to enable the improvement and sustainability of Bt-based products. Although downregulation of the expression of midgut receptor genes is a pivotal mechanism of insect resistance to Bt Cry toxins, the underlying transcriptional regulation of these genes remains elusive. Herein, we unraveled the regulatory mechanism of the downregulation of the ABC transporter gene PxABCG1 (also called Pxwhite), a functional midgut receptor of the Bt Cry1Ac toxin in Plutella xylostella. The PxABCG1 promoters of Cry1Ac-susceptible and Cry1Ac-resistant strains were cloned and analyzed, and they showed clear differences in activity. Subsequently, a dual-luciferase reporter assay, a yeast one-hybrid (Y1H) assay, and RNA interference (RNAi) experiments demonstrated that a cis-mutation in a binding site of the Hox transcription factor Antennapedia (Antp) decreased the promoter activity of the resistant strain and eliminated the binding and regulation of Antp, thereby enhancing the resistance of P. xylostella to the Cry1Ac toxin. These results advance our knowledge of the roles of cis- and trans-regulatory variations in the regulation of midgut Cry receptor genes and the evolution of Bt resistance, contributing to a more complete understanding of the Bt resistance mechanism.

Evidence for the Involvement of the Chemosensory Protein AgosCSP5 in Resistance to Insecticides in the Cotton Aphid, Aphis gossypii.

Simple SummaryInsect chemosensory proteins (CSPs) are potential targets for insect pest control strategies and are proposed to function in insect chemoreception, because they play a role in crop host location by binding and transporting odorant molecules. They are also thought to have other functions, for example, in tissue regeneration and in insecticide resistance, because they also express in nonolfactory tissues and are capable of binding insecticides. However, there are few reports that provide direct evidence for this proposal. In this study, we discovered gene gain-and-loss among aphid populations, possibly associated with different insecticide resistance, and then identified and cloned a CSP gene responsive to insecticide treatments. The introduction of such gene in Drosophila fruit flies made the transgenic flies less sensitive to the treatment of different insecticides. Our study advances the research of insect CSP functions and offers valuable new information to target CSPs for pest management.It has been speculated that insect chemosensory proteins (CSPs) may have additional roles beyond olfaction. In this study, the phylogenetic and genomic analyses of the CSPs of the cotton aphid, Aphis gossypii, revealed the presence of gene gain-and-loss among different aphid field populations. Differential expressions of eight CSP genes were demonstrated after treatments with insecticides of different modes of action. The expression of AgosCSP5 was significantly upregulated by the insecticide treatments in a dose-dependent manner. The Drosophila flies overexpressing AgosCSP5 were significantly less susceptible to the insecticides, omethoate, imidacloprid and cypermethrin but not to deltamethrin and tau-fluvalinate, compared with control flies. The transgenic Drosophila flies exhibited an LC50 resistance ratio of 2.6 to omethoate, compared with control flies. Likewise, the mortality of the transgenic flies to imidacloprid and cypermethrin was significantly lower than that of the control flies (p < 0.01). Homology modelling, molecular docking and dynamic simulation supported the interactions and revealed a higher stability of AgosCSP5/insecticide complexes than AgosCSP5/semiochemical complexes. Our study demonstrates for first time the in vivo evidence for the involvement of CSP genes in insecticide resistance of crop insect pests and provides new insights of the newly discovered CSP-mediated insect resistance mechanism to insecticides.

Biosafety of bee pollinators in genetically modified agro-ecosystems: Current approach and further development in the EU.

Bee pollinators are an important guild delivering a fundamental input to European agriculture due to the ecological service they provide to crops in addition to the direct economic revenues from apiculture. Bee populations are declining in Europe as a result of the effects of several environmental stressors, both natural and of anthropic origin. Efforts are ongoing in the European Union (EU) to improve monitoring and management of pollinator populations to arrest further declines. Genetically modified (GM) crops are currently cultivated in a limited area in Europe, and an environmental risk assessment (ERA) is required prior to their authorization for cultivation. The possible impacts of GM crops on pollinators are deemed relevant for the ERA. Existing ecotoxicological studies indicate that traits currently expressed in insect‐resistant GM plants are unlikely to represent a risk for pollinators. However, new mechanisms of insect resistance are being introduced into GM plants, including novel combinations of Cry toxins and double strand RNA (dsRNA), and an ERA is required to consider lethal and sublethal effects of these new products on nontarget species, including insect pollinators. The evaluation of indirect effects linked to the changes in management practices (e.g. for herbicide‐tolerant GM crops) is an important component of EU regulations and a requirement for ERA. This paper reviews current approaches used to test the sensitivity of pollinators to GM plants and their products to determine whether sufficient data are being provided on novel GM plants to satisfy EU risk assessment requirements. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Full-length transcriptome and targeted metabolome analyses provide insights into defense mechanisms of Malus sieversii against Agrilus mali.

Malus sieversii is the wild progenitor for many cultivars of domesticated apple and an important germplasm resource for breeding. However, this valuable species faces a significant threat in the areas north of the Tianshan Mountains in China, by the invasion of Agrilus mali, a destructive pest of apple trees belonging to the family Buprestidae. Our preliminary study has has shown that there may be resistance to this insect in M. sieversii plants in the field, but the corresponding molecular mechanisms remain unclear. In this study, we compared the response of insect-resistant and insect-susceptible plants of M. sieversii to insect feeding using full-length transcriptome and targeted metabolome. 112,103 non-chimeric full-length reads (FLNC) totaling 10.52 Gb of data were generating with Pacific Biosciences SingleMolecule, Real-Time (PacBio SMRT) sequencing. A total of 130.06 Gb data of long reads were acquired with an Illumina HiSeq. Function annotation indicated that the different expressed genes (DEGs) were mainly involved in signal transduction pathway of plant hormones and in the synthesis of compounds such as terpenes, quinones, flavonoids, and jasmonic acid. Through targeted metabolome analysis resistant strains showed higher levels of trans-cinnamic acid, caffeine and ferulic acid after pest infestation. This study helps to decipher the transcriptional changes and related signaling paths in M. sieversii after an insect feeding, which lays a foundation for further research on molecular mechanisms of insect resistance in apples.

Low expression levels of nicotinic acetylcholine receptor subunits Boα1 and Boβ1 are associated with imidacloprid resistance in Bradysia odoriphaga.

Neonicotinoid insecticide imidacloprid acts on insect nicotinic acetylcholine receptors (nAChRs). The mechanisms of insect resistance to imidacloprid include target-site alteration and increased detoxification metabolism. In Bradysia odoriphaga, cytochrome P450 monooxygenase has been found involved in metabolic resistance to imidacloprid. However, the situation of target-site related resistance to imidacloprid in B. odoriphaga is still unknown. Nine field-collected B. odoriphaga populations showed various sensitivities to imidacloprid compared with the susceptible (SS) strain, including susceptibility, decreased susceptibility, low resistance, moderate resistance and high resistance. Seven nAChR subunit genes including α1, α2, α3, α7, α8, β1 and β3, were examined for site mutation and changes in transcription levels in field populations. No nAChR polymorphism potentially related to the resistant phenotypes was found. However, differential expression of nAChR subunit genes was found in imidacloprid resistant field population. In high imidacloprid resistant population LC-2 (93.14-fold resistance), the transcription levels of α1, α2 and β1 subunits were significantly down-regulated, while the transcription levels of α3 and α8 subunits were significantly up-regulated, compared with that in SS strain. In addition, imidacloprid acute exposure induced differential expression of nAChR subunit genes in B. odoriphaga. Furthermore, RNA interference (RNAi) suppressed the transcriptional expression of Boα1 and Boβ1, and decreased mortality of B. odoriphaga by 23.03% and 18.69%, respectively, when treated with imidacloprid. These results indicated that, although no target-site mutation was found in imidacloprid resistant B. odoriphaga population, the reduced expression of α1 and β1 subunits contributed to B. odoriphaga resistance to imidacloprid. © 2020 Society of Chemical Industry.

A Wild Cajanus scarabaeoides (L.), Thouars, IBS 3471, for Improved Insect-Resistance in Cultivated Pigeonpea

Cajanus scarabaeoides (L.), Thouars, is the closest wild crop relative of cultivated pigeonpea, Cajanus cajan (L.), Millspaugh. This wild pigeonpea has several insect-resistance mechanisms, particularly to Helicoverpa armigera (Hübner). Estimated economic losses in the semi-arid tropics from H. armigera damage in pigeonpea are approximately two billion USD/year. Therefore, it is imperative to improve pest resistance in this crop. In this study, we investigated insect-resistance components in IBS 3471, a C. scarabaeoides accession, and explored the possibility of transferring resistance mechanism/s to cultivated pigeonpea. A detached leaf bioassay revealed that IBS 3471 has more effective antibiosis and antixenosis resistance mechanisms against H. armigera compared to the susceptible C. cajan variety, ICPL 87. To further investigate the antibiosis resistance mechanism, we fed H. armigera larvae a heated and non-heated artificial diet supplemented with lyophilised IBS 3471 leaf powder. Incorporation of IBS 3471 leaf powder inhibited H. armigera larval weight and delayed larval development compared to larvae reared on diet supplemented with ICPL 87 leaf powder. The putative insect-resistance compounds in C. scarabaeoides were heat-labile. Proteomic analysis revealed higher levels of potential insecticidal proteins, namely lectin and cysteine proteinase inhibitor, in wild pigeonpea compared to the cultivated variety. Nutritional analysis and interspecific hybridisation experiments also indicated that IBS 3471 is a potential candidate for improvement of insect-resistance in pigeonpea. This study demonstrates that IBS 3471 has multiple resistance mechanisms against H. armigera, and they are transferable to cultivated pigeonpea.

Bacillus thuringiensis vegetative insecticidal protein family Vip3A and mode of action against pest Lepidoptera.

Vip3A proteins are widely used for controlling pest Lepidoptera. Different binding sites with different receptors in the insect midgut membrane and lack of cross-resistance with crystal (Cry) proteins enhance their applicability, as both single proteins and proteins pyramided with Cry proteins in transgenic Bt crops. Vip3A proteins are effective but there is relatively little information about their structure, function, activation, specificity, and mode of action. In addition, the mechanism of insect resistance to these proteins is unknown. Phylogenetic analysis and multiple sequence alignment showed that Vip3A proteins are genetically distant from Cry proteins. The mode of action and insecticidal activity of Vip3A proteins are discussed in this review. This review also provides detailed information about the Vip3A protein family that may aid in the design of more efficient pest management strategies in response to insect resistance to insecticidal proteins. © 2020 Society of Chemical Industry.