Modulation of fatty acid elongation in cockroaches sustains sexually dimorphic hydrocarbons and female attractiveness

Regulatory changes in the fatty acid elongase eloF underlie the evolution of sex-specific pheromone profiles in Drosophila prolongata

BACKGROUND

Pheromones play a key role in regulating sexual behavior throughout the animal kingdom. In Drosophila and other insects, many cuticular hydrocarbons (CHCs) are sexually dimorphic, and some are known to perform pheromonal functions. However, the genetic control of sex-specific CHC production is poorly understood outside of the model species D. melanogaster. A recent evolutionary change is found in D. prolongata, which, compared to its closest relatives, shows greatly increased sexual dimorphism in both CHCs and the chemosensory system responsible for their perception. A key transition involves a male-specific increase in the proportion of long-chain CHCs.

RESULTS

Perfuming D. prolongata females with the male-biased long-chain CHCs reduces copulation success, suggesting that these compounds function as sex pheromones. The evolutionary change in CHC profiles correlates with a male-specific increase in the expression of multiple genes involved in CHC biosynthesis, including fatty acid elongases, reductases and other key enzymes. In particular, elongase F, which is responsible for producing female-specific pheromones in D. melanogaster, is strongly upregulated in D. prolongata males compared both to females and to males of the sibling species. Mutations in eloF reduce the amount of long-chain CHCs, resulting in a partial feminization of pheromone profiles in D. prolongata males. Transgenic experiments show that sex-biased expression of eloF is caused in part by a putative transposable element honghaier insertion in its regulatory region.

CONCLUSIONS

These results show that cis-regulatory changes in the eloF gene, along with other changes in the CHC synthesis pathway, contribute to the evolution of sexual communication.

Regulation of insect cuticular hydrocarbon biosynthesis

Cuticular hydrocarbons (CHCs) play pleiotropic roles in insect survival and reproduction. They prevent desiccation and function as pheromones influencing different behaviors. While the genes in the CHC biosynthesis pathway have been extensively studied, the regulatory mechanisms that lead to different CHC compositions received far less attention. In this review, we present an overview of how different hormones and transcriptional factors regulate CHC synthesis genes, leading to different CHC compositions. Future research focusing on the regulatory mechanisms underlying CHC biosynthesis can lead to a better understanding of how insects could produce dynamic chemical profiles in response to different stimuli.

The role of intraspecific mechanical and chemical signaling for mate and sexual recognition in male Tityus pusillus (Scorpiones, Buthidae)

Hydrophobic compounds present in the cuticular wax layer (CWL) of terrestrial arthropods protect them from dehydration and are also involved in chemical communication. However, the role of CWL compounds in the behavioral ecology of scorpions has been studied less often, with most investigations focusing on their responses to mechanical stimuli. In this study, we aimed to characterize the CWL composition of Tityus pusillus (Scorpiones, Buthidae) and examine the influence of CWL solvent extracts and movement on intraspecific mate and sexual recognition by males of this species. We analyzed CWL hexane extracts of adult female and male T. pusillus by gas chromatography-mass spectrometry (GC-MS). In paired behavioral tests inside an experimental arena, we exposed adult males to i) live and intact dead conspecific females; ii) intact dead females and females without the CWL (removed with solvent washes); and iii) intact dead males with and without the CWL. Our results showed that CWL extracts of both female and male T. pusillus contained a series of linear alkanes (C21 - C34; > 54 % relative composition), as well as fatty acyls (> 9.5 %) and methyl-branched alkanes (> 9.1 %). Two unassigned C31 monomethyl-branched alkanes were exclusively identified in male CWL extracts (∼ 4.7 %), while female samples contained high relative concentrations (> 22.5 %) of sterol derivatives, present only as minor constituents in male samples. Male T. pusillus performed sexually-oriented behavioral acts when paired with both live and dead conspecific females, intact or without the CWL. However, they ignored conspecific dead males. Our results show that CWL compounds have a role in intraspecific sexual recognition by male T. pusillus but only the CWL compounds does not explain mate recognition.

Screening and identification of antimicrobial peptides from the gut microbiome of cockroach Blattella germanica

BACKGROUND

The overuse of antibiotics has led to lethal multi-antibiotic-resistant microorganisms around the globe, with restricted availability of novel antibiotics. Compared to conventional antibiotics, evolutionarily originated antimicrobial peptides (AMPs) are promising alternatives to address these issues. The gut microbiome of Blattella germanica represents a previously untapped resource of naturally evolving AMPs for developing antimicrobial agents.

RESULTS

Using the in-house designed tool "AMPidentifier," AMP candidates were mined from the gut microbiome of B. germanica, and their activities were validated both in vitro and in vivo. Among filtered candidates, AMP1, derived from the symbiotic microorganism Blattabacterium cuenoti, demonstrated broad-spectrum antibacterial activity, low cytotoxicity towards mammalian cells, and a lack of hemolytic effects. Mechanistic studies revealed that AMP1 rapidly permeates the bacterial cell and accumulates intracellularly, resulting in a gradual and mild depolarization of the cell membrane during the initial incubation period, suggesting minimal direct impact on membrane integrity. Furthermore, observations from fluorescence microscopy and scanning electron microscopy indicated abnormalities in bacterial binary fission and compromised cell structure. These findings led to the hypothesis that AMP1 may inhibit bacterial cell wall synthesis. Furthermore, AMP1 showed potent antibacterial and wound healing effects in mice, with comparable performances of vancomycin.

CONCLUSIONS

This study exemplifies an interdisciplinary approach to screening safe and effective AMPs from natural biological tissues, and our identified AMP 1 holds promising potential for clinical application.

Genetic Underpinnings of Cuticular Hydrocarbon Biosynthesis in the German Cockroach, Blattella germanica (L.): Progress and Perspectives

Insect cuticular hydrocarbons (CHCs) serve as important waterproofing barriers and as signals and cues in chemical communication. Over the past 30 years, numerous studies on CHCs have been conducted in the German cockroach, Blattella germanica, leading to substantial progress in the field. However, there has not been a systematic review of CHC studies in this species in recent years. This review aims to provide a concise overview of the chemical composition, storage, transport, and physical properties of different CHCs in B. germanica. Additionally, we focus on the biosynthetic pathway and the genetic regulation of HC biosynthesis in this species. A considerable amount of biochemical evidence regarding the biosynthetic pathway of insect CHCs has been gathered from studies conducted in B. germanica. In recent years, there has also been an improved understanding of the molecular mechanisms that underlie CHC production in this insect. In this article, we summarize the biosynthesis of different classes of CHCs in B. germanica. Then, we review CHCs reaction to various environmental conditions and stressors and internal physiological states. Additionally, we review a body of work showing that in B. germanica, CHC profiles exhibit significant sexual dimorphism, specific CHCs act as essential precursors for female contact sex pheromone components, and we summarize the molecular regulatory mechanisms that underlie sexual dimorphism of CHC profiles. Finally, we highlight future directions and challenges in research on the biosynthesis and regulatory mechanisms of CHCs in B. germanica, and also identify potential applications of CHC studies in the pest control.

Lipid Metabolism as a Target Site in Pest Control

Lipid metabolism is essential to insect life as insects use lipids for their development, reproduction, flight, diapause, and a wide range of other functions. The central organ for insect lipid metabolism is the fat body, which is analogous to mammalian adipose tissue and liver, albeit less structured. Various other systems including the midgut, brain, and neural organs also contribute functionally to insect lipid metabolism. Lipid metabolism is under the control of core lipogenic [e.g. acetyl-CoA-carboxylase (ACC), fatty acid synthase (FAS), perilipin 2 (LSD2)], and lipolytic (lipases, perilipin 1) enzymes that are primarily expressed in the fat body, as well as hormones [insulin-like peptides (ILP), adipokinetic hormone (AKH)], transcription factors (SREBPs, foxO, and CREB), secondary messengers (calcium) and post-translational modifications (phosphorylation). Essential roles of the fat body, together with the fact that proper coordination of lipid metabolism is critical for insects, render lipid metabolism an attractive target site in pest control. In the current chapter, we focus on pest control tactics that target insect lipid metabolism. Various classes of traditional chemical insecticides [e.g. organophosphates, pyrethroids, neonicotinoids, and chitin synthesis inhibitors (Sects. 2.1 and 2.2)] have been shown to interfere with lipid metabolism, albeit it is not their primary site of action. However, the discovery of "lipid biosynthesis inhibitors", tetronic and tetramic acid derivatives commonly known as ketoenols (Sect. 2.3), was a milestone in applied entomology as they directly target lipid biosynthesis, particularly in sucking pests. Spirodiclofen, spiromesifen, and spirotetramat targeting ACC act against various insect and mite pests, while spiropidion and spidoxamat have been introduced to the market only recently. Efforts have concentrated on the development of chemical alternatives, such as hormone agonists and antagonists (Sect. 2.4), dsRNA-based pesticides that depend on RNA interference, which have great potential in pest control (Sect. 2.5) and other eco-friendly alternatives (Sect. 2.6).

Regulatory Changes in the Fatty Acid Elongase eloF Underlie the Evolution of Sex-specific Pheromone Profiles in Drosophila prolongata

Pheromones play a key role in regulating sexual behavior throughout the animal kingdom. In Drosophila and other insects, many cuticular hydrocarbons (CHCs) are sexually dimorphic, and some are known to perform pheromonal functions. However, the genetic control of sex-specific CHC production is not understood outside of the model species D. melanogaster. A recent evolutionary change is found in D. prolongata, which, compared to its closest relatives, shows greatly increased sexual dimorphism in both CHCs and the chemosensory system responsible for their perception. A key transition involves a male-specific increase in the proportion of long-chain CHCs. Perfuming D. prolongata females with the male-biased CHCs reduces copulation success, suggesting that these compounds function as sex pheromones. The evolutionary change in CHC profiles correlates with a male-specific increase in the expression of multiple genes involved in CHC biosynthesis, including fatty acid elongases and reductases and other key enzymes. In particular, elongase F, which is responsible for producing female-specific pheromones in D. melanogaster, is strongly upregulated in D. prolongata males compared both to females and to males of the sibling species. Induced mutations in eloF reduce the amount of long-chain CHCs, resulting in a partial feminization of pheromone profiles in D. prolongata males while having minimal effect in females. Transgenic experiments show that sex-biased expression of eloF is caused in part by a putative transposable element insertion in its regulatory region. These results reveal one of the genetic mechanisms responsible for a recent evolutionary change in sexual communication.

Chemical and transcriptomic diversity do not correlate with ascending levels of social complexity in the insect order Blattodea

Eusocial insects, such as ants and termites, are characterized by high levels of coordinated social organization. This is contrasted by solitary insects that display more limited forms of collective behavior. It has been hypothesized that this gradient in sociobehavioral sophistication is positively correlated with chemical profile complexity, due to a potentially increased demand for diversity in chemical communication mechanisms in insects with higher levels of social complexity. However, this claim has rarely been assessed empirically. Here, we compare different levels of chemical and transcriptomic complexity in selected species of the order Blattodea that represent different levels of social organization, from solitary to eusocial. We primarily focus on cuticular hydrocarbon (CHC) complexity, since it has repeatedly been demonstrated that CHCs are key signaling molecules conveying a wide variety of chemical information in solitary as well as eusocial insects. We assessed CHC complexity and divergence between our studied taxa of different social complexity levels as well as the differentiation of their respective repertoires of CHC biosynthesis gene transcripts. Surprisingly, we did not find any consistent pattern of chemical complexity correlating with social complexity, nor did the overall chemical divergence or transcriptomic repertoire of CHC biosynthesis genes reflect on the levels of social organization. Our results challenge the assumption that increasing social complexity is generally reflected in more complex chemical profiles and point toward the need for a more cautious and differentiated view on correlating complexity on a chemical, genetic, and social level.

Acetyl coenzyme A carboxylase modulates lipogenesis and sugar homeostasis in Blattella germanica

Lipid and sugar homeostasis is critical for insect development and survival. In this study, we characterized an acetyl coenzyme A carboxylase gene in Blattella germanica (BgACC) that is involved in both lipogenesis and sugar homeostasis. We found that BgACC was dominantly expressed in the fat body and integument, and was significantly upregulated after molting. Knockdown of BgACC in 5th-instar nymphs did not affect their normal molting to the next nymphal stage, but it caused a lethal phenotype during adult emergence. BgACC-RNA interference (RNAi) significantly downregulated total free fatty acid (FFA) and triacylglycerol (TAG) levels, and also caused a significant decrease of cuticular hydrocarbons (CHCs). Repression of BgACC in adult females affected the development of oocytes and resulted in sterile females, but BgACC-RNAi did not affect the reproductive ability of males. Interestingly, knockdown of BgACC also changed the expression of insulin-like peptide genes (BgILPs), which mimicked a physiological state of high sugar uptake. In addition, BgACC was upregulated when B. germanica were fed on a high sucrose diet, and repression of BgACC upregulated the expression of the glycogen synthase gene (BgGlyS). Moreover, BgACC-RNAi increased the circulating sugar levels and glycogen storage, and a longevity assay suggested that BgACC was important for the survival of B. germanica under conditions of high sucrose uptake. Our results confirm that BgACC is involved in multiple lipid biogenesis and sugar homeostasis processes, which further modulates insect reproduction and sugar tolerance. This study benefits our understanding of the crosstalk between lipid and sugar metabolism.

Female semiochemicals stimulate male courtship but dampen female sexual receptivity

Chemical communication plays a vital role in mate attraction and discrimination among many insect species. Here, we document a unique example of semiochemical parsimony, where four chemicals act as both aphrodisiacs and anti-aphrodisiacs in different contexts in Bactrocera dorsalis. Specifically, we identified four female-specific semiochemicals, ethyl laurate, ethyl myristate, ethyl cis-9-hexadecenoate, and ethyl palmitate, which serve as aphrodisiacs to attract male flies and arouse male courtship. Interestingly, these semiochemicals, when sexually transferred to males during mating, can function as anti-aphrodisiacs, inhibiting the receptivity of subsequent female mates. We further showed that the expression of elongase11, a key enzyme involved in the biosynthesis of these semiochemicals, is under the control of doublesex, facilitating the exclusive biosynthesis of these four semiochemicals in females and guaranteeing effective chemical communication. The dual roles of these semiochemicals not only ensure the attractiveness of mature females but also provide a simple yet reliable mechanism for female mate discrimination. These findings provide insights into chemical communication in B. dorsalis and add elements for the design of pest control programs.

Chemical communication and its role in sexual selection across Animalia

Sexual selection has been studied as a major evolutionary driver of animal diversity for roughly 50 years. Much evidence indicates that competition for mates favors elaborate signaling traits. However, this evidence comes primarily from a few taxa, leaving sexual selection as a salient evolutionary force across Animalia largely untested. Here, we reviewed the evidence for sexual selection on communication across all animal phyla, classes, and orders with emphasis on chemoreception, the only sense shared across lifeforms. An exhaustive literature review documented evidence for sexual selection on chemosensory traits in 10 of 34 animal phyla and indications of sexual selection on chemosensory traits in an additional 13 phyla. Potential targets of sexual selection include structures and processes involved in production, delivery, and detection of chemical signals. Our review suggests sexual selection plays a widespread role in the evolution of communication and highlights the need for research that better reflects animal diversity.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte Nuclear Factor 4

Sexual attraction and perception are crucial for mating and reproductive success. In Drosophila melanogaster, the male-specific isoform of Fruitless (Fru), FruM, is a known master neuro-regulator of innate courtship behavior to control the perception of sex pheromones in sensory neurons. Here, we show that the non-sex-specific Fru isoform (FruCOM) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of FruCOM in oenocytes resulted in adults with reduced levels of cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 (Hnf4) as a key target of FruCOM in directing fatty acid conversion to hydrocarbons. Fru or Hnf4 depletion in oenocytes disrupts lipid homeostasis, resulting in a sex-dimorphic CHC profile that differs from doublesex- and transformer-dependent CHC dimorphism. Thus, Fru couples pheromone perception and production in separate organs to regulate chemosensory communications and ensure efficient mating behavior.

An Acyl Carrier Protein Gene Affects Fatty Acid Synthesis and Growth of Hermetia illucens

Acyl carrier protein (ACP) is an acyl carrier in fatty acid synthesis and is an important cofactor of fatty acid synthetase. Little is known about ACP in insects and how this protein may modulate the composition and storage of fatty acids. We used an RNAi-assisted strategy to study the potential function of ACP in Hermetia illucens (Diptera: Stratiomyidae). We identified a HiACP gene with a cDNA length of 501 bp and a classical conserved region of DSLD. This gene was highly expressed in the egg and late larval instars and was most abundant in the midgut and fat bodies of larvae. Injection of dsACP significantly inhibited the expression level of HiACP and further regulated the fatty acid synthesis in treated H. illucens larvae. The composition of saturated fatty acids was reduced, and the percentage of unsaturated fatty acids (UFAs) was increased. After interfering with HiACP, the cumulative mortality of H. illucens increased to 68.00% (p < 0.05). H. illucens growth was greatly influenced. The development duration increased to 5.5 days, the average final body weights of larvae and pupae were decreased by 44.85 mg and 14.59 mg, respectively, and the average body lengths of larvae and pupae were significantly shortened by 3.09 mm and 3.82 mm, respectively. The adult eclosion rate and the oviposition of adult females were also severely influenced. These results demonstrated that HiACP regulates fatty acid content and influences multiple biological processes of H. illucens.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte nuclear factor 4

Sexual attraction and perception, governed by separate genetic circuits in different organs, are crucial for mating and reproductive success, yet the mechanisms of how these two aspects are integrated remain unclear. In Drosophila , the male-specific isoform of Fruitless (Fru), Fru M , is known as a master neuro-regulator of innate courtship behavior to control perception of sex pheromones in sensory neurons. Here we show that the non-sex specific Fru isoform (Fru COM ) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of Fru COM in oenocytes resulted in adults with reduced levels of the cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 ( Hnf4 ) as a key target of Fru COM in directing fatty acid conversion to hydrocarbons in adult oenocytes. fru - and Hnf4 -depletion disrupts lipid homeostasis, resulting in a novel sex-dimorphic CHC profile, which differs from doublesex - and transformer -dependent sexual dimorphism of the CHC profile. Thus, Fru couples pheromone perception and production in separate organs for precise coordination of chemosensory communication that ensures efficient mating behavior.

Teaser

Fruitless and lipid metabolism regulator HNF4 integrate pheromone biosynthesis and perception to ensure robust courtship behavior.

Intrasexual cuticular hydrocarbon dimorphism in a wasp sheds light on hydrocarbon biosynthesis genes in Hymenoptera

Cuticular hydrocarbons (CHCs) cover the cuticle of insects and serve as desiccation barrier and as semiochemicals. While the main enzymatic steps of CHC biosynthesis are well understood, few of the underlying genes have been identified. Here we show how exploitation of intrasexual CHC dimorphism in a mason wasp, Odynerus spinipes, in combination with whole-genome sequencing and comparative transcriptomics facilitated identification of such genes. RNAi-mediated knockdown of twelve candidate gene orthologs in the honey bee, Apis mellifera, confirmed nine genes impacting CHC profile composition. Most of them have predicted functions consistent with current knowledge of CHC metabolism. However, we found first-time evidence for a fatty acid amide hydrolase also influencing CHC profile composition. In situ hybridization experiments furthermore suggest trophocytes participating in CHC biosynthesis. Our results set the base for experimental CHC profile manipulation in Hymenoptera and imply that the evolutionary origin of CHC biosynthesis predates the arthropods' colonization of land.

Melanin synthesis genes BgTH and BgDdc affect body color and cuticle permeability in Blattella germanica

Melanin is involved in cuticle pigmentation and sclerotization of insects, which is critical for maintaining structural integrity and functional completeness of insect cuticle. The 2 key enzymes of tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) predicted in melanin biosynthesis are usually conserved in insects. However, it is unclear whether their function is related to epidermal permeability. In this study, we identified and cloned the gene sequences of BgTH and BgDdc from Blattella germanica, and revealed that they both showed a high expression at the molting, and BgTH was abundant in the head and integument while BgDdc was expressed highest in the fat body. Using RNA interference (RNAi), we found that knockdown of BgTH caused molting obstacles in some cockroaches, with the survivors showing pale color and softer integuments, while knockdown of BgDdc was viable and generated an abnormal light brown body color. Desiccation assay showed that the dsBgTH-injected adults died earlier than control groups under a dry atmosphere, but dsBgDdc-injected cockroaches did not. In contrast, when dsRNA-treated cockroaches were reared under a high humidity condition, almost no cockroaches died in all treatments. Furthermore, with eosin Y staining assay, we found that BgTH-RNAi resulted in a higher cuticular permeability, and BgDdc-RNAi also caused slight dye penetration. These results demonstrate that BgTH and BgDdc function in body pigmentation and affect the waterproofing ability of the cuticle, and the reduction of cuticular permeability may be achieved through cuticle melanization.

A single gene integrates sex and hormone regulators into sexual attractiveness

Sex differentiation and hormones are essential for the development of sexual signals in animals, and the regulation of sexual signals involves complex gene networks. However, it is unknown whether a core gene is able to connect the upstream regulators for controlling sexual signal outputs and behavioural consequences. Here, we identify a single gene that integrates both sex differentiation and hormone signalling with sexual attractiveness in an insect model. CYP4PC1 in the German cockroach, Blattella germanica, controls the rate-limiting step in producing female-specific contact sex pheromone (CSP) that stimulates male courtship. As revealed by behavioural, biochemical, molecular, genetic and bioinformatic approaches, in sexually mature females, CYP4PC1 expression and CSP production are coordinately induced by sex differentiation genes and juvenile hormone (JH) signalling. In adult males, direct inhibition of CYP4PC1 expression by doublesex^M binding in gene promoter and lack of the gonadotropic hormone JH prevent CSP production, thus avoiding male-male attraction. By manipulating the upstream regulators, we show that wild-type males prefer to court cockroaches with higher CYP4PC1 expression and CSP production in a dose-dependent manner, regardless of their sex. These findings shed light on how sex-specific and high sexual attractiveness is conferred in insects.

Evolutionary History of Sexual Differentiation Mechanism in Insects

Alternative splicing underpins functional diversity in proteins and the complexity and diversity of eukaryotes. An example is the doublesex gene, the key transcriptional factor in arthropod sexual differentiation. doublesex is controlled by sex-specific splicing and promotes both male and female differentiation in holometabolan insects, whereas in hemimetabolan species, doublesex has sex-specific isoforms but is not required for female differentiation. How doublesex evolved to be essential for female development remains largely unknown. Here, we investigate ancestral states of doublesex using Thermobia domestica belonging to Zygentoma, the sister group of Pterygota, that is, winged insects. We find that, in T. domestica, doublesex expresses sex-specific isoforms but is only necessary for male differentiation of sexual morphology. This result supports the hypothesis that doublesex initially promoted male differentiation during insect evolution. However, T. domestica doublesex has a short female-specific region and upregulates the expression of vitellogenin homologs in females, suggesting that doublesex may already play some role in female morphogenesis of the common ancestor of Pterygota. Reconstruction of the ancestral sequence and prediction of protein structures show that the female-specific isoform of doublesex has an extended C-terminal disordered region in holometabolan insects but not in nonholometabolan species. We propose that doublesex acquired its function in female morphogenesis through a change in the protein motif structure rather than the emergence of the female-specific exon.

Neglected Very Long-Chain Hydrocarbons and the Incorporation of Body Surface Area Metrics Reveal Novel Perspectives for Cuticular Profile Analysis in Insects

Simple Summary

The waxy layer covering the surface of most terrestrial insects is mainly composed of non-polar lipids termed cuticular hydrocarbons (CHCs). These have a long research history as important dual traits for both desiccation prevention and chemical communication. We analyzed CHC profiles of seven species of the insect order Blattodea (termites and cockroaches) with the most commonly applied chromatographic method, gas-chromatography coupled with mass spectrometry (GC-MS), and the more novel approach of silver-assisted laser desorption/ionization mass spectrometry (Ag-LDI-MS). Comparing these two analytical methods, we demonstrated that the conventional GC-MS approach does not provide enough information on the entire CHC profile range in the tested species. Ag-LDI-MS was able to detect very long-chain CHCs ranging up to C58, which remained undetected when solely relying on standard GC-MS analysis. Additionally, we measured the body surface areas of each tested species applying 3D scanning technology to assess their respective CHC amounts per mm². When adjusting for body surface areas, proportional CHC quantity distributions shifted considerably between our studied species, suggesting the importance of including this factor when conducting quantitative CHC comparisons, particularly in insects that vary substantially in body size.

Abstract

Most of our knowledge on insect cuticular hydrocarbons (CHCs) stems from analytical techniques based on gas-chromatography coupled with mass spectrometry (GC-MS). However, this method has its limits under standard conditions, particularly in detecting compounds beyond a chain length of around C40. Here, we compare the CHC chain length range detectable by GC-MS with the range assessed by silver-assisted laser desorption/ionization mass spectrometry (Ag-LDI-MS), a novel and rarely applied technique on insect CHCs, in seven species of the order Blattodea. For all tested species, we unveiled a considerable range of very long-chain CHCs up to C58, which are not detectable by standard GC-MS technology. This indicates that general studies on insect CHCs may frequently miss compounds in this range, and we encourage future studies to implement analytical techniques extending the conventionally accessed chain length range. Furthermore, we incorporate 3D scanned insect body surface areas as an additional factor for the comparative quantification of extracted CHC amounts between our study species. CHC quantity distributions differed considerably when adjusted for body surface areas as opposed to directly assessing extracted CHC amounts, suggesting that a more accurate evaluation of relative CHC quantities can be achieved by taking body surface areas into account.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Evaluation of Reference Genes for Transcriptional Profiling in Two Cockroach Models

The German cockroach, Blattella germanica, and the American cockroach, Periplaneta americana are the most common and synanthropic household pests of interest to public health. While they have increasingly served as model systems in hemimetabolous insects for studying many biological issues, there is still a lack of stable reference gene evaluation for reliable quantitative real-time PCR (qPCR) outputs and functional genomics. Here, we evaluated the expression variation of common insect reference genes, including the historically used actin, across various tissues and developmental stages, and also under experimental treatment conditions in these two species by using three individual algorithms (geNorm, BestKeeper, and NormFinder) and a comprehensive program (RefFinder). RPL32 in B. germanica and EF1α in P. americana showed the overall lowest variation among all examined samples. Based on the stability rankings by RefFinder, the optimal but varied reference genes under specific conditions were selected for qPCR normalization. In addition, the combination of RPL32 and EF1α was recommended for all the tested tissues and stages in B. germanica, whereas the combination of multiple reference genes was unfavorable in P. americana. This study provides a condition-specific resource of reference gene selection for accurate gene expression profiling and facilitating functional genomics in these two important cockroaches.