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According to the World Health Organization vector-borne diseases account for more than 17% of all infectious diseases, causing more than 700,000 deaths annually. Vectors are organisms that are able to transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are hematophagous insects, which ingest the pathogen from an infected host during a blood meal, and later transmit it into a new host. Malaria, dengue, African trypanosomiasis, yellow fever, leishmaniasis, Chagas disease, and many others are examples of diseases transmitted by insects.Both the diet and the infection with pathogens trigger changes in many metabolic pathways, including lipid metabolism, compared to other insects. Blood contains mostly proteins and is very poor in lipids and carbohydrates. Thus, hematophagous insects attempt to efficiently digest and absorb diet lipids and also rely on a large de novo lipid biosynthesis based on utilization of proteins and carbohydrates as carbon source. Blood meal triggers essential physiological processes as molting, excretion, and oogenesis; therefore, lipid metabolism and utilization of lipid storage should be finely synchronized and regulated regarding that, in order to provide the necessary energy source for these events. Also, pathogens have evolved mechanisms to hijack essential lipids from the insect host by interfering in the biosynthesis, catabolism, and transport of lipids, which pose challenges to reproduction, survival, fitness, and other insect traits.In this chapter, we have tried to collect and highlight the current knowledge and recent discoveries on the metabolism of lipids in insect vectors of diseases related to the hematophagous diet and pathogen infection., (© 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

The Triatoma sordida subcomplex traditionally included four triatomine species, T. sordida, Triatoma garciabesi, Triatoma guasayana, and Triatoma patagonica, distributed in the Southern Cone of South America. These species have a large intraspecific variability together with an overall similarity, making difficult to establish their taxonomic status. Many cytogenetic, morphometric, and molecular markers have been applied to address this. Recent studies have posed concerns on the inclusion of T. guasayana and T. patagonica within the subcomplex. Also, T. sordida from Argentina has been designed as a new species, Triatoma rosai. Using the cuticular hydrocarbon pattern as chemotaxonomic marker, the relationships among several populations of these species were analyzed by capillary gas chromatography and linear discriminant analysis along 25 collection sites in Argentina, Bolivia, Brazil, and Paraguay. T. sordida and T. rosai populations were differentially clustered in two CHC-based groups: "Group 1" included T. sordida from Eastern Brazil, Eastern Paraguay, and the Bolivian populations from La Paz and Izozog G1; "Group 2" included T. rosai, and T. sordida from Izozog G2 (Bolivia), and Western Paraguay. Whereas T. garciabesi remained closely related to T. sordida and T. rosai, T. guasayana, and T. patagonica were clearly separated from the species of the T. sordida subcomplex. Our results agree with those from other several techniques suggesting that the taxonomy of the T. sordida subcomplex should be revised., (© The Author(s) 2021. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: The redbanded stink bug Piezodorus guildinii (Heteroptera: Pentatomidae) is one of the most important species affecting soybean crops in southern South America. Capillary gas chromatography coupled to mass spectrometry was used to characterize the epicuticular hydrocarbon profiles of field-collected insects, and to identify differences in their composition between fifth-instar nymphs and adults, males and females, and between bugs collected in insecticide-treated and insecticide-free soybean crops., Results: Straight chain saturated n-C27 and n-C29, and monomethyl and dimethyl chains of C31 and C33 were the most abundant compounds. A group of volatile hydrocarbons with n-C13 and n-C15 as the predominant compounds were also detected. The hydrocarbon pattern was different between nymphs and adults, either males or females. Heneicosene was almost exclusively detected in adult males and was the most important component to differentiate between both sexes, followed by tricosadiene. The total hydrocarbon amount was significantly higher in nymphs, males and females collected in insecticide-treated fields compared with insects obtained from untreated fields., Conclusion: Differences were found in the epicuticular hydrocarbon pattern among nymphs and adults, as well as sexual dimorphism in adult stink bugs. Interestingly, an alteration was also found in the hydrocarbon profile of insects collected in insecticide-treated soybean crops and its relevance is discussed within a pest management context., (© 2021 Society of Chemical Industry.)

Insect cuticle hydrocarbons are involved primarily in waterproofing the cuticle, but also participate in chemical communication and regulate the penetration of insecticides and microorganisms. The last step in insect hydrocarbon biosynthesis is carried out by an insect-specific cytochrome P450 of the 4G subfamily (CYP4G). Two genes (CYP4G106 and CYP4G107) have been reported in the triatomines Rhodnius prolixus and Triatoma infestans. In this work, their molecular and functional characterization is carried out in R. prolixus, and their relevance to insect survival is assessed. Both genes are expressed almost exclusively in the integument and have an expression pattern dependent on the developmental stage and feeding status. CYP4G106 silencing diminished significantly the straight-chain hydrocarbon production while a significant reduction - mostly of methyl-branched chain hydrocarbons - was observed after CYP4G107 silencing. Molecular docking analyses using different aldehydes as hydrocarbon precursors predicted a better fit of straight-chain aldehydes with CYP4G106 and methyl-branched aldehydes with CYP4G107. Survival bioassays exposing the silenced insects to desiccation stress showed that CYP4G107 is determinant for the waterproofing properties of the R. prolixus cuticle. This is the first report on the in vivo specificity of two CYP4Gs to make mostly straight or methyl-branched hydrocarbons, and also on their differential contribution to insect desiccation., (© 2020 The Royal Entomological Society.)

Fatty acid synthase is a multifunctional enzyme involved in the formation of fatty acids. Despite the role of fatty acids in cell signalling and energy metabolism, and as precursors to pheromones and hydrocarbons that waterproof the cuticle, the insect fatty acid synthases have been scarcely studied. Here we perform the molecular characterization of three fatty acid synthase genes (fatty acid synthase RPRC000123, RPRC000269 and RPRC002909) in the Chagas disease vector, Rhodnius prolixus. Gene expression screening by reverse transcription quantitative PCR showed that RPRC000123 and RPRC002909 are expressed almost exclusively in the integument tissue whilst RPRC000269 is mostly expressed in the fat body and also in several body organs. Phylogenetic analysis, together with gene expression results, showed that RPRC000269, RPRC002909 and RPRC000123 are orthologues of Drosophila melanogaster fatty acid synthase 1 (FASN1), FASN2 and FASN3 genes, respectively. After RNA interference-mediated knockdown of RPRC000123, insects died immediately after moulting to the next developmental stage. However, mortality was prevented by placing the insects under saturated humidity conditions, suggesting that dehydration might play a role in the insects' death. Lipid analyses in RPRC000123-silenced insects showed reduced amounts of integument fatty acids and methyl-branched hydrocarbons, compared to controls. These data support an important role for FASN3 in the biosynthesis of the precursors to hydrocarbons that waterproof the insect cuticle., (© 2019 The Royal Entomological Society.)

Insect resistance to chemical insecticides is attributed to a combination of different mechanisms, such as metabolic resistance, knockdown resistance, and the cuticular resistance or penetration factor. The insect integument offers an efficient barrier against contact insecticides and its role as penetration factor has been previously reported; however, there is no information about its potential function in the metabolic resistance. Cytochrome P450 genes (CYP) are highly expressed in the fat body of several insects and thus play a key role in their metabolic resistance. Here, we describe new members that belong to the highly genome-wide expanded CYP3093A and CYP4EM subfamilies in the Chagas disease vectors Rhodnius prolixus and Triatoma infestans. We modeled the docking of deltamethrin in their active site and detected differences in some amino acids between both species that are critical for a correct interaction with the substrate. We also knocked down the two constitutively most expressed genes in the integument of resistant T. infestans nymphs (CYP3093A11 and CYP4EM10) in order to find clues on their participation in deltamethrin resistance. This is the first report on the role of the insect integument in detoxification events; although these two CYP genes do not fully explain the resistance observed in T. infestans.

The insect integument, formed by the cuticle and the underlying epidermis, is essential for insect fitness, regulation of lipid biosynthesis and storage, insect growth and feeding, together with development progress. Its participation in insecticide resistance has also been outlined. Triatoma infestans Klug (Hemiptera: Reduviidae) is one of the major vectors of Chagas disease in South America; however, genomic data are scarce. In this study, we performed a transcriptome analysis of the nymph integument in order to identify which genes are expressed and their putative role. Using the 454 GS-FLX sequencing platform, we obtained approximately 144,620 reads from the integument tissue. These reads were assembled into 6,495 isotigs and 8,504 singletons. Based on BLAST similarity searches, about 8,000 transcripts were annotated with known genes, conserved domains, and/or Gene Ontology terms.The most abundant transcripts corresponded to transcription factors and nucleic acid metabolism, membrane receptors, cell signaling, and proteins related to cytoskeleton, transport, and cell energy processes, among others. More than 10% of the transcripts-encoded proteins putatively involved in the metabolism of fatty acids and related components (fatty acid synthases, elongases, desaturases, fatty alcohol reductases), structural integument proteins, and the insecticide detoxification system (among them, cytochrome P450s, esterases, and glutathione transferases). Real-time qPCR assays were used to investigate their putative participation in the resistance mechanism. This preliminary study is the first transcriptome analysis of a triatomine integument, and together with prior biochemical information, will help further understandthe role of the integument in a wide array of mechanisms., (© The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The kissing bug Rhodnius prolixus is both an important vector of Chagas' disease and an interesting model for investigation into the field of physiology, including lipid metabolism. The publication of this insect genome will bring a huge amount of new molecular biology data to be used in future experiments. Although this work represents a promising scenario, a preliminary analysis of the sequence data is necessary to identify and annotate the genes involved in lipid metabolism. Here, we used bioinformatics tools and gene expression analysis to explore genes from different genes families and pathways, including genes for fat breakdown, as lipases and phospholipases, and enzymes from β-oxidation, fatty acid metabolism, and acyl-CoA and glycerolipid synthesis. The R. prolixus genome encodes 31 putative lipase genes, including 21 neutral lipases and 5 acid lipases. The expression profiles of some of these genes were analyzed. We were able to identify nine phospholipase A2 genes. A variety of gene families that participate in fatty acid synthesis and modification were studied, including fatty acid synthase, elongase, desaturase and reductase. Concerning the synthesis of glycerolipids, we found a second isoform of glycerol-3-phosphate acyltransferase that was ubiquitously expressed throughout the organs. Finally, all genes involved in fatty acid β-oxidation were identified, but not a long-chain acyl-CoA dehydrogenase. These results provide fundamental data to be used in future research on insect lipid metabolism and its possible relevance to Chagas' disease transmission., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Metamorphosis, which depends upon a fine balance between two groups of lipid-soluble hormones such as juvenile hormones (JHs) and ecdysteroids, is an important feature in insect evolution. While it is clear that the onset of metamorphosis depends on the decrease of JH levels, the way in which these hormones exert their activities is not fully understood in Triatominae species. The discovery of a Drosophila melanogaster mutant resistant to the treatment with the JH analog methoprene, led finally to the description of the methoprene-tolerant gene in Tribolium castaneum (TcMet) as a putative JH receptor. Here we present the genomic and functional characterization of an ortholog of the methoprene-tolerant gene in the hemimetabolous insect Rhodnius prolixus (RpMet). The analysis of the R. prolixus gene showed that the exonic structure is different from that described for holometabolous species, although all the critical protein motifs are well conserved. Expression analysis showed the presence of RpMet mRNA in all the tested tissues: ovary, testis, rectum, Malpighian tubules and salivary glands. When juvenile individuals were treated with RpMet specific double strand RNA (dsRNA), we observed abnormal molting events that resulted in individuals with morphological alterations (adultoids). Similarly, treatment of newly emerged fed females with dsRNA resulted in an abnormal development of the ovaries, with eggs revealing anomalies in size and accumulation of yolk, as well as a decrease in the amount of heme-binding protein. Altogether, our results validate that RpMet is involved in the transduction of JH signaling, controlling metamorphosis and reproduction in R. prolixus., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The cuticular hydrocarbons of the Triatoma sordida subcomplex (Hemiptera: Reduviidae: Triatominae) were ana-lysed by gas chromatography and their structures identified by mass spectrometry. They comprised mostly n-alkanes and methyl-branched alkanes with one-four methyl substitutions. n-alkanes consisted of a homologous series from C21-C33 and represented 33-45% of the hydrocarbon fraction; n-C29 was the major component. Methyl-branched alkanes showed alkyl chains from C24-C43. High molecular weight dimethyl and trimethylalkanes (from C35-C39) represented most of the methyl-branched fraction. A few tetramethylalkanes were also detected, comprising mostly even-numbered chains. Several components such as odd-numbered 3-methylalkanes, dimethylalkanes and trimethylalkanes of C37 and C39 showed patterns of variation that allowed the differentiation of the species and populations studied. Triatoma guasayana and Triatoma patagonica showed the most distinct hydrocarbon patterns within the subcomplex. The T. sordida populations from Brazil and Argentina showed significantly different hydrocarbon profiles that posed concerns regarding the homogeneity of the species. Triatoma garciabesi had a more complex hydrocarbon pattern, but it shared some similarity with T. sordida. The quantitative and qualitative variations in the cuticular hydrocarbons may help to elucidate the relationships between species and populations of this insect group.

Triatoma infestans Klug (Hemiptera: Reduviidae) populations were sampled in various localities throughout most of the species' geographic range of distribution in Argentina, Bolivia, Paraguay and Peru. In order to contribute to understanding of the diversity and population structure of this major vector of Chagas' disease, cuticular hydrocarbon (CHC) profiles were analysed by capillary gas chromatography and variations evaluated by statistical methods of classification and ordination. High levels of intrapopulation variation were detected, along with low levels of variability among populations. Based on relative amounts of the major odd-numbered straight-chain hydrocarbons n-C27 to n-C33, two hydrocarbon phenotypes were evident, unequally distributed along the species' geographic range. Analysis of CHC patterns showed that T. infestans populations segregate into two major groups consisting of an Andean group, which comprises specimens from Peru and most parts of Bolivia, and a non-Andean group, which includes all specimens from Argentina and Paraguay, together with those from Tarija (Bolivia). Pyrethroid-resistant and -susceptible specimens were differentiated based on relative amounts of some straight and monomethyl-branched hydrocarbon components., (© 2011 The Authors. Medical and Veterinary Entomology © 2011 The Royal Entomological Society.)

Triatoma dimidiata Latreille is a major vector of Chagas disease with an extensive geographic distribution from Central Mexico, through Central America, to northern South America. As a result of its variability in phenetic and genetic characters, disagreement concerning its taxonomic status has been raised. In this study, the cuticular hydrocarbon pattern of T. dimidiata populations from Mexico, Belize, Guatemala, Honduras, Costa Rica, and Colombia was analyzed by capillary gas chromatography coupled to mass spectrometry; linear discriminant analysis was used to help elucidate population structure. Vector populations segregated into five distinct groups; specimens from Yucatan Peninsula, together with those from Central Mexico, Central America, and Colombia corresponded to different T. dimidiata subspecies, a putative different species comprising insects from Belize, together with an isolated population collected at bat caves in Guatemala. The analysis revalidates the earlier division of T dimidiata into three subspecies, T. d. maculipennis, T. d. dimidiata, and T. d. capitata; and an additional subspecies and a distinct species are proposed.