Molecular bases of P450-mediated resistance to the neonicotinoid insecticide imidacloprid in the mosquito Ae. aegypti

Effect of pyriproxyfen on biological parameters and morphometry of Aedes aegypti Linnaeus, 1762 (Diptera: Culicidae) in the city of Manaus, Amazonas

In Brazil, Aedes aegypti is the primary vector of arboviruses, and its control relies mainly on insecticide use. However, excessive application on these products has led to the selection of resistant populations. To address this challenge, products like Pyriproxyfen (PPF), an insect growth regulator, have been used as a viable alternative. In this context, the present study evaluated the susceptibility, resistance ratio, and biological changes of A. aegypti exposed to PPF. Samples were collected in eight neighborhoods using oviposition traps, and the Rockefeller strain was used as a susceptibility standard. Fecundity tests recorded a hatching rate of 72.4 % in the PPF groups, compared to 89.2 % in the control (p < 0.05), and fertility of 72.4 % for PPF compared to 89.2 % in the control (t = 204.5, df = 4, p < 0.05). Longevity was assessed in males, females, and couples (χ² = 20.35, df = 5, p > 0.05). Wing morphometric analyses were reinforced by Mahalanobis distance (1.7127; p < 0.001), Procrustes analysis (0.0064; p = 0.5027), and canonical variable analyses. The width of the cephalic capsules was greater in mosquitoes exposed to PPF (Mann-Whitney U = 369; p < 0.0099). The emergence inhibition rate ranged from 65.33 ± 4 to 100 ± 0 for the Rockefeller strain and from 59.33 ± 4 to 88.66 ± 2 for the field population, with a resistance ratio of 0.68. The study concludes that the A. aegypti population in Manaus, remains susceptible to PPF, and the observed alterations were not significant enough to compromise the vector's biology.

Transcription factor CREB/ATF regulates overexpression of CYP6CY14 conferring resistance to cycloxaprid in Aphis gossypii

Aphis gossypii Glover as a destructive agricultural pest has evolved resistance to various insecticides. Cycloxaprid is a novel structure neonicotinoid insecticide with excellent toxicity against A. gossypii. However, the resistance mechanism of A. gossypii to cycloxaprid was unclear. In the present study, a cycloxaprid-resistant (Cpd-R) strain (80.1-fold) of A. gossypii was obtained by continuous selection. Bioassay results showed that piperonyl butoxide significantly increased the toxicity of cycloxaprid by 10.5-fold to the Cpd-R strain. The activity of P450s was significantly higher in Cpd-R strain than in susceptible (Cpd-S) strain. The transcriptomic and qRT-PCR results showed that CYP6CY14, CYP380C44 and CYP303A1 were significantly upregulated in Cpd-R strain compared with Cpd-S strain. Furthermore, knockdown of CYP6CY14, CYP380C44 and CYP303A1 via RNA interference (RNAi) significantly increased the sensitivity of Cpd-R strain to cycloxaprid. Based on the higher expression of CYP6CY14 and RNAi results, transgenic Drosophila assay was conducted to further clarify the role of CYP6CY14 in cycloxaprid resistance, and results showed a significant increase in resistance to cycloxaprid in D. melanogaster. Additionally, the results of RNAi, dual-luciferase reporter and yeast one-hybrid (Y1H) indicated that CREB/ATF directly regulates CYP6CY14 expression. These findings provide necessary basis for clarifying the resistance mechanism of cycloxaprid in A. gossypii.

The Dual Resistance Mechanism of CYP325G4 and CYP6AA9 in Culex pipiens pallens Legs According to Transcriptome and Proteome Analysis

Mosquitoes within the Culex pipiens complex play a crucial role in human disease transmission. Insecticides, especially pyrethroids, are used to control these vectors. Mosquito legs are the main entry point and barrier for insecticides to gain their neuronal targets. However, the resistance mechanism in mosquito legs is unclear. Herein, we employed transcriptomic analyses and isobaric tags for relative and absolute quantitation techniques to investigate the resistance mechanism, focusing on Cx. pipiens legs. We discovered 2346 differentially expressed genes (DEGs) between deltamethrin-resistant (DR) and deltamethrin-sensitive (DS) mosquito legs, including 41 cytochrome P450 genes. In the same comparison, we identified 228 differentially expressed proteins (DEPs), including six cytochrome P450 proteins. Combined transcriptome and proteome analysis revealed only two upregulated P450 genes, CYP325G4 and CYP6AA9. The main clusters of DEGs and DEPs were associated with metabolic processes, such as cytochrome P450-mediated metabolism of drugs and xenobiotics. Transcription analysis revealed high CYP325G4 and CYP6AA9 expression in the DR strain at 72 h posteclosion compared with that in the DS strain, particularly in the legs. Mosquitoes knocked down for CYP325G4 were more sensitive to deltamethrin than the controls. CYP325G4 knockdown reduced the expression of several chlorinated hydrocarbon (CHC)-related genes, which altered the cuticle thickness and structure. Conversely, CYP6AA9 knockdown increased CHC gene expression without altering cuticle thickness and structure. P450 activity analysis demonstrated that CYP325G4 and CYP6AA9 contributed to metabolic resistance in the midgut and legs. This study identified CYP325G4 as a novel mosquito deltamethrin resistance factor, being involved in both metabolic and cuticular resistance mechanisms. The previously identified CYP6AA9 was investigated for its involvement in metabolic resistance and potential cuticular resistance in mosquito legs. These findings enhance our comprehension of resistance mechanisms, identifying P450s as promising targets for the future management of mosquito vector resistance, and laying a theoretical groundwork for mosquito resistance management.

Larvicidal and enzyme inhibition effects of Phoenix pusilla derived Methyl oleate and malathion on Aedes aegypti strains

This study explores the larvicidal potential of methanolic flower extracts from Phoenix pusilla (Pp-Fe), its major compound, and malathion (MLT), against laboratory strain (LS) and field strain (FS) of Aedes aegypti, the dengue mosquito vector. We identified thirty-one derivatives, with methyl oleate (MO) comprising 28.5% of Pp-Fe. Comparative efficacy evaluations were performed using peak dosages of Pp-Fe (500 ppm), MO (5 ppm), and MLT (5 ppm) on LS and FS larvae. Both LS and FS second instars showed higher susceptibility to Pp-Fe (95% and 93%, respectively) and MO (85% and 83%, respectively). MLT resulted in significant mortality rates among LS larvae (98%) and notable reductions among FS larvae (71%). The expression levels of key biomarker enzymes (carboxylesterase, GST, and CYP450) exhibited a consistent decrease and subsequent upregulation in LS and FS larvae following exposure to Pp-Fe and MO, contrasting with the significant expression variations observed in LS and FS larvae exposed to MLT. LS larvae demonstrated heightened susceptibility and evident midgut cell damage following all treatments, suggesting potential disparities in susceptibility and adaptive responses between LS and FS strains towards MLT. These observations underscore the promising larvicidal attributes of Pp-Fe and MO, emphasizing the need for further exploration of their mechanisms of action in the development of environmentally sustainable mosquito control strategies and resistance management.

CYP6CX2 and CYP6CX3 mediate thiamethoxam resistance in field whitefly, Bemisia tabaci (Hemiptera:Aleyrodidae)

Cytochrome P450 monooxygenases (P450s) are well-known for their crucial roles in the detoxification of xenobiotics. However, whether CYP6CX2 and CYP6CX3, 2 genes from our Bemisia tabaci (B. tabaci) MED/Q genome data were associated with detoxification metabolism and confer resistance to thiamethoxam is unclear. In this study, we investigated the role of CYP6CX2 and CYP6CX3 in mediating whitefly thiamethoxam resistance. Our results showed that mRNA levels of CYP6CX2 and CYP6CX3 were up-regulated after exposure to thiamethoxam. Transcriptional levels of 2 genes were overexpressed in laboratory and field thiamethoxam resistant strains by RT-qPCR. These results indicate that the enhanced expression of CYP6CX2 and CYP6CX3 appears to confer thiamethoxam resistance in B. tabaci. Moreover, linear regression analysis showed that the expression levels of CYP6CX2 and CYP6CX3 were positively correlated with thiamethoxam resistance levels among populations. The susceptibility of whitefly adults was markedly increased after silencing 2 genes by RNA interference (RNAi) which further confirming their major role in thiamethoxam resistance. Our findings provide information to better understand the roles of P450s in resistance to neonicotinoids and suggest that these genes may be applied to develop target genes for sustainable management tactic of agricultural pests such as B. tabaci.

Recent Advancements in Pathogenic Mechanisms, Applications and Strategies for Entomopathogenic Fungi in Mosquito Biocontrol

Fungal diseases are widespread among insects and play a crucial role in naturally regulating insect populations. Mosquitoes, known as vectors for numerous infectious diseases, pose a significant threat to human health. Entomopathogenic fungi (EPF) have emerged as highly promising alternative agents to chemical mosquitocides for controlling mosquitoes at all stages of their life cycle due to their unique infection pathway through direct contact with the insect's cuticle. In recent years, significant advancements have been made in understanding the infection pathways and pathogenic mechanisms of EPF against mosquitoes. Various strategies involving the use of EPF alone or combinations with other approaches have been employed to target mosquitoes at various developmental stages. Moreover, the application of genetic technologies in fungi has opened up new avenues for enhancing the mosquitocidal efficacy of EPF. This review presents a comprehensive summary of recent advancements in our understanding the pathogenic mechanisms of EPF, their applications in mosquito management, and the combination of EPF with other approaches and employment of transgenic technologies. The biosafety concerns associated with their use and the corresponding approaches are also discussed. The recent progress suggests that EPF have the potential to serve as a future biorational tool for controlling mosquito vectors.

Discovery and structure-activity relationship of Morita-Baylis-Hillman adducts as larvicides against dengue mosquito vector, Aedes aegypti (Diptera: Culicidae)

Neglected tropical diseases (NTDs) have become a significant public health problem worldwide, notably the life-threatening dengue hemorrhagic fever borne by the Aedes aegypti mosquito. Thus, mosquito vector control measures remain essential in public health vector surveillance and control to combat Aedes-borne infections. Therefore, a series of MBH adducts were synthesized and assessed towards the fourth instar mosquito larvae, Aedes aegypti, along with the preliminary structure-activity relationship (SAR). Noteworthy, this compound class might be synthetized by an efficient eco-friendly synthesismethod and a rapid route for the synthesis of commercial larvicide through a single synthetic step. The bioassays showed that this compound class is a promising larvicide to control Aedes aegypti mosquito larvae, mainly 3g, with an LC₅₀ of 41.35 µg/mL, which was higher than evaluated positive controls. Nevertheless, it is a viable larvicidalhit candidate for further hit-to-leadproperties optimization of its biphenyl backbone scaffold with enhanced insecticidalbioactivity. Moreover, scanning electron microscopy analysis suggested a disruption of the osmoregulatory/ionoregulatory functions by the complete deterioration of the terminal exoskeleton hindgut and anal papillae. Therefore, this new study shows the larvicidal efficacy of the tested compounds against the Aedes aegypti larvae.

Functional Validation of the Roles of Cytochrome P450s in Tolerance to Thiamethoxam and Imidacloprid in a Field Population of Aphis gossypii

Field populations of Aphis gossypii (SDR) have evolved high resistance to neonicotinoids, including thiamethoxam and imidacloprid. Synergism bioassays and transcriptomic comparison of the SDR and susceptible (SS) strains revealed that the cytochrome P450s may contribute to the neonicotinoid resistance evolution. The transcripts of some P450s were constitutively overexpressed in the SDR strain, and many genes showed expression plasticity under insecticide exposure. Drosophila that ectopically expressed CYPC6Y9, CYP4CK1, CYP6DB1, and CYP6CZ1 showed greater resistance (>8.0-fold) to thiamethoxam, and Drosophila that expressed CYPC6Y9, CYP6CY22, CYP6CY18, and CYP6D subfamily genes showed greater resistance (>5-fold) to imidacloprid. Five P450 genes that caused thiamethoxam resistance also conferred resistance to α-cypermethrin. Furthermore, the knockdown of CYP4CK1, CYP6CY9, CYP6CY18, CYPC6Y22, CYP6CZ1, and CYP6DB1 dramatically increased the sensitivity of the SDR strain to thiamethoxam or imidacloprid. These results indicate the involvement of multiple P450 genes, rather than one key gene, in neonicotinoid resistance in field populations.

Transcriptome analysis of Mythimna separata: De novo assembly and detection of genes related to beta-cypermethrin resistance

The oriental armyworm Mythimna separata (Walker) is a devastating pest of cereal crops mainly in Asia and Oceania and recently become resistant to beta-cypermethrin (beta-CP). However, molecular biological studies of its response to beta-CP are scarce, and related genomic information is not available. In this study, we sequenced and de novo assembled the transcriptome of beta-CP susceptible M. separata (MsS-whole, abbr. MsS-W). A total of 30,486 unigenes were obtained, with an N50 length of 506 bp. A number of 21,051 unigenes were matched to public databases, of which 10,107 were classified into 59 gene ontology subcategories, 5792 were assigned into 25 clusters of orthologous groups of proteins subgroups and 12,123 were assigned to 257 Kyoto Encyclopedia of Genes and Genomes pathways. A total of 729 simple sequence repeats were detected. In addition, a total of 323 cytochrome P450-associated sequences from nine lepidopterous species, of which 130 were from M. separata, were analyzed using the maximum likelihood method and Bayesian inference. Among the 130 cytochrome P450-associated sequences from M. separata, 60 were dropped into CYP3 clan, which is associated with metabolizing xenobiotics and plant natural compounds. Furthermore, the beta-CP susceptible (MsS-2) and resistant (MsR-2) M. separata population transcriptomes were sequenced. Certain critical genes involved in beta-CP detoxification were detected and verified by quantitative real-time polymerase chain reaction. Collectively, our results provided a basis for further studies of the molecular mechanism of insecticide resistance in M. separata.

Crosstalk Between GABAergic Neurotransmission and Inflammatory Cascades in the Post-ischemic Brain: Relevance for Stroke Recovery

Adaptive plasticity processes are required involving neurons as well as non-neuronal cells to recover lost brain functions after an ischemic stroke. Recent studies show that gamma-Aminobutyric acid (GABA) has profound effects on glial and immune cell functions in addition to its inhibitory actions on neuronal circuits in the post-ischemic brain. Here, we provide an overview of how GABAergic neurotransmission changes during the first weeks after stroke and how GABA affects functions of astroglial and microglial cells as well as peripheral immune cell populations accumulating in the ischemic territory and brain regions remote to the lesion. Moreover, we will summarize recent studies providing data on the immunomodulatory actions of GABA of relevance for stroke recovery. Interestingly, the activation of GABA receptors on immune cells exerts a downregulation of detrimental anti-inflammatory cascades. Conversely, we will discuss studies addressing how specific inflammatory cascades affect GABAergic neurotransmission on the level of GABA receptor composition, GABA synthesis, and release. In particular, the chemokines CXCR4 and CX3CR1 pathways have been demonstrated to modulate receptor composition and synthesis. Together, the actual view on the interactions between GABAergic neurotransmission and inflammatory cascades points towards a specific crosstalk in the post-ischemic brain. Similar to what has been shown in experimental models, specific therapeutic modulation of GABAergic neurotransmission and inflammatory pathways may synergistically promote neuronal plasticity to enhance stroke recovery.

Susceptibility of Field-Collected Nyssorhynchus darlingi to Plasmodium spp. in Western Amazonian Brazil

Mosquito susceptibility to Plasmodium&nbsp;spp. infection is of paramount importance for malaria occurrence and sustainable transmission. Therefore, understanding the genetic features underlying the mechanisms of susceptibility traits is pivotal to assessing malaria transmission dynamics in endemic areas. The aim of this study was to investigate the susceptibility of Nyssorhynchus darlingi-the dominant malaria vector in Brazil-to Plasmodium spp. using a reduced representation genome-sequencing protocol. The investigation was performed using a genome-wide association study (GWAS) to identify mosquito genes that are predicted to modulate the susceptibility of natural populations of the mosquito to Plasmodium infection. After applying the sequence alignment protocol, we generated the variant panel and filtered variants; leading to the detection of 202,837 SNPs in all specimens analyzed. The resulting panel was used to perform GWAS by comparing the pool of SNP variants present in Ny.&nbsp;darlingi infected with Plasmodium spp. with the pool obtained in field-collected mosquitoes with no evidence of infection by the parasite (all mosquitoes were tested separately using RT-PCR). The GWAS results for infection status showed two statistically significant variants adjacent to important genes that can be associated with susceptibility to Plasmodium infection: Cytochrome P450 (cyp450) and chitinase. This study provides relevant knowledge on malaria transmission dynamics by using a genomic approach to identify mosquito genes associated with susceptibility to Plasmodium infection in Ny. darlingi in western Amazonian Brazil.